POPULATION RESPONSE OF A DECLINING SONGBIRD TO SILVICULTURE: HOW CERULEAN
WARBLER (SETOPHAGA CERULEA) TERRITORY SIZE AND SETTLEMENT PATTERNS FARE IN
THE FACE OF FOREST DISTURBANCE
A THESIS SUBMITTED TO THE GRADUATE SCHOOL
IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE
MASTER OF SCIENCE
BY
RYAN H. DIBALA
BALL STATE UNIVERSITY
ADVISOR: DR. KAMAL ISLAM
MUNCIE, INDIANA
MAY 2012
ii
ABSTRACT
DISSERTATION/THESIS/RESEARCH PAPER/CREATIVE PROJECT: Population response of a
declining songbird to silviculture: How Cerulean Warbler (Setophaga cerulea) territory
size and settlement patterns fare in the face of forest disturbance
STUDENT: Ryan H. Dibala
DEGREE: Master of Science
COLLEGE: Sciences and Humanities
DATE: May 2012
PAGES: 110
Over the past 5 decades, populations of the Cerulean Warbler (Setophaga
cerulea) have declined precipitously and the response of populations to silviculture has
been identified as a high-priority research need. This species was studied in nine forest
management units in Southern Indiana following a harvest that took place in 2008.
Males were detected, territories were demarcated, and male age-class was determined
to identify settlement patterns. Vegetation was measured in all territories and
associated random non-use sites. Data analyzed in ArcMap (ArcGIS 10) show that
Cerulean Warbler territory size was smallest and density was highest in even-aged units.
Territories contained a greater number of small woody species than non-use sites but
no vegetative differences existed between male age-classes. Instead, males appeared
to select areas by relying on social cues from experienced neighbors. It is possible that
“social attraction” management techniques could influence male Cerulean Warbler
settlement patterns, providing a valuable tool for the conservation of this species.
iii
Acknowledgments
This research would not have been possible without financial assistance from
IDNR/Purdue University, US Fish and Wildlife Service, Amos W. Butler Audubon Society,
Indiana Academy of Science, and Ball State University Internal Grants Program (ASPiRE).
I am grateful for the continual help and support of Jennifer Wagner while in the
field. She is one of the most inquisitive people I know and has helped me redefine
myself as a field biologist and free thinker. The amount of data collected and strides we
have made in better understanding the Cerulean Warbler would not have been possible
without the hard work of David Rupp, Jordan Schindler, Amy Wilson, and Edsel
Koscielniak. I am lucky to have had such a hard-working and dedicated group of
technicians. We all learned so much from each other throughout our summer together.
I would also like to thank Erin Arnold for her invaluable assistance in data entry.
I am forever indebted to my advisor and mentor Dr. Kamal Islam who guided me
patiently and faithfully every step of the way. He was a joy to be around and always
encouraged me to explore new avenues in research and to think outside the box. His
excitement and passion for nature has inspired me to continue teaching and conducting
research. I’d also like to thank Carol Islam for all her support, help, and kindness
throughout my two years at Ball State.
I would also like to thank Dr. David LeBlanc for his guidance and help with
statistical analyses. Through his teaching, he has given me a solid foundation with
which to continue research. Additionally, I thank Dr. Kevin Turcotte for his help with GIS
and Drs. Keanre Eouanzoui and Kemuel Badger along with Stephen Jacquemin for their
help with the vegetation data analysis.
Big ups to my main man David Sturgeon, who has been an amazing source of
motivation and positive affirmation. He created a space for me in his house and has left
an imprint on my heart. I thank him for his friendship. Last but certainly not least I
thank my parents Richard and Karen and my sister Christie. I would not have had this
incredible opportunity to explore the natural world and try to make some sense of its
iv
mystery if it weren’t for my amazing family. They exposed me to inquiry at a young age
and have continually supported me in all of my endeavors. I love you and wouldn’t have
been able to do this without you!
v
Table of Contents
Abstract………………………………………………………………………………………………………………………… ii
Acknowledgments……………………………………………………………………………………………………….. iii
Table of Contents…………………………………………………………………………………………………………. v
Thesis Summary…………………………………………………………………………………………………………… 1
Chapter 1
Forest Management Effects on Cerulean Warbler
Territory Size in Southern Indiana………………………………………………………………………………… 7
Chapter 2
Conspecific Social Cues Strongly Influence Cerulean
Warbler Male Settlement Patterns in a Managed Forest................................................ 42
Appendix I………………………………………………………………………………………………………………….. 83
Appendix II…………………………………………………………………………………………………………………. 98
Appendix III………………………………………………………………………………………………………………. 103
1
Thesis Summary
The Cerulean Warbler (Setophaga cerulea) is a Nearctic-Neotropical migrant
songbird that breeds in mature, contiguous deciduous forest in eastern and central
North America and winters on the slopes of the Andes Mountains of northwestern
South America (Hamel 2000). Over the past five decades, numbers of Cerulean
Warblers are estimated to have dropped approximately 70% and now this species is
experiencing the greatest decline of any North American wood warbler (Sauer et al.
2008). The Cerulean Warbler has quickly become the poster child for many migratory
birds that have been affected by the loss of contiguous forest cover in both their
breeding and wintering grounds, and various conservation and habitat management
plans have been erected in hopes of restoring populations throughout its range.
Cerulean Warbler response to land management activities such as silviculture
has been identified as a high-priority research need (Hamel 2000, Hamel et al. 2004).
Some authors have suggested that Cerulean Warblers may be attracted to canopy gaps
or openings and these gaps may be an important aspect of nest-site selection (Bent
1953, Oliarnyk 1996, Oliarnyk and Robertson 1996). Conversely, there has been concern
that too many openings within a forest’s interior could maximize edge-effects and
internally fragment what once was continuous forest (Annand and Thompson 1997).
Thus, it is critical to evaluate Cerulean Warbler population response to various levels of
forest disturbance.
2
During the summers of 2010 and 2011, I studied a population of Cerulean
Warblers at Yellowwood and Morgan-Monroe state forests in Southern Indiana to
assess the effects of even-aged and uneven-aged silviculture on male territory size.
Additionally, in 2011, I investigated age-specific male settlement patterns to examine
behavioral and social cues that influence territory establishment in a managed forest.
Ultimately, understanding an animal’s behavior may be just as important for
conservation as understanding its environment (Clemmons and Buchholz 1997). In order
to make informed management decisions that ultimately ensure Cerulean Warbler
conservation, I analyzed both vegetative components and social mechanisms that may
be important to this species.
Chapter 1 presents results of male territory sizes over five years in nine
management units at Yellowwood and Morgan-Monroe state forests in Southern
Indiana. Uneven and even-aged harvests were implemented in the fall of 2008 across
six of nine managements units; three control sites received no treatment. Cerulean
Warbler territory size was not significantly different between pre- and post-treatment
years. However, there were a greater number of territories that were significantly
smaller in even-aged units than they were in control units. It is difficult to determine
the long-term effects of even-aged silviculture because songbirds often exhibit a lag
response to disturbance (Brooks et al. 1999), but Cerulean Warblers seem to be
attracted to even-aged units in these forests.
3
Chapter 2 focuses on research conducted in 2011 on age-specific male
settlement patterns. I recorded male age-class along with territory size and found that
yearling male territories were significantly larger than mature adult male territories.
Although no statistical difference was found in clustering between age-classes, smaller
territory sizes may mean that mature adult males often settle in higher-density areas
than yearlings. In fact, a comparison of average nearest neighboring territories showed
that mature adults had significantly closer neighbors than did yearlings. Both ageclasses settled significantly closer to other mature adult males, indicating that this
species shows a clear preference for settling closer to experienced adults. There was no
difference in vegetative structure and distance to important habitat features between
the age-classes, providing evidence that male Cerulean Warbler settlement patterns are
strongly influenced by conspecific social cues.
Many species of birds have been shown to be attracted to areas where they
experience poor survival or reproductive success, especially in human-altered
landscapes (Gates and Gysel 1978, Wilcove 1985). In the Appalachian Mountains, Boves
(2011) found that although Cerulean Warbler territory density and body condition was
highest after intermediate and heavy forest disturbance, reproductive success was
significantly lower. Cerulean Warblers in Yellowwood and Morgan-Monroe state forests
had lower reproductive success in both even and uneven-aged areas than control areas
(Jennifer Wagner unpublished data). Even-aged areas could be serving as ecological
4
traps that could ultimately have a negative impact on the population (Pärt et al. 2007,
Boves 2011).
For species that are highly sensitive to conspecific attraction, conservationists
could use broadcast vocalizations known as playbacks to attract birds to settle in known
high-quality habitats (Mills et al. 2006, Alatalo et al. 1982, Muller et al. 1997). It is
possible that vulnerable songbirds like the Cerulean Warbler could be coaxed into
settling on protected lands where limiting factors can be controlled and breeding
success may be higher. This may prove to be an important management tool to prevent
further decline of this denizen of the deciduous forest.
5
Literature Cited
Alatalo, R. V., A. Lundberg, and M. Bjorklund. 1982. Can the song of male birds attract
other males? An experiment with the Pied Flycatcher Ficedula hypoleuca. Bird
Behaviour 4:42-45.
Annand, E. M. and F. R. Thompson III. 1997. Forest bird response to regeneration
practices in central hardwood forests. Journal of Wildlife Management 61:159
171.
Bent, A. C. 1953. Life Histories of North American Wood Warblers, parts I and II. Dover
Publications, New York.
Boves, T. J. 2011. Multiple responses by Cerulean Warblers to experimental forest
disturbance in the Appalachian Mountains. PhD dissertation, University of
Tennessee, Knoxville, TN.
Brooks, T. M., S. L. Pimm, and J. O. Oyugi. 1999. Time lags between deforestation and
bird extinction in tropical forest fragments. Conservation Biology 13:1140-1150.
Clemmons, J. R., and R. Buchholz, editors. 1997. Behavioral approaches to conservation
in the wild. Cambridge University Press, New York.
Gates, J. E., and L. W. Gysel. 1978. Avian nest dispersion and fledging success in field
forest ecotones. Ecology 59:871–883.
Hamel, P. B. 2000. Cerulean Warbler (Dendroica cerulea). The Birds of North America,
No. 511 (A. Poole and F. Gill, eds.). The Birds of North America, Inc.,
Philadelphia, PA.
Hamel, P. B., D. K. Dawson, and P. D. Keyser. 2004. How we can learn more about the
Cerulean Warbler (Dendroica cerulea). Auk 121:7-14.
Mills, A. M., J. D. Rising and D. A. Jackson. 2006. Conspecific attraction during
establishment of Least Flycatcher clusters. Journal of Field Ornithology 77:34-38.
Muller, K. L., J. A. Stamps, V. V. Krishnan, and N. H. Willits. 1997. The effects of
conspecific attraction and habitat quality on habitat selection in territorial birds
(Troglodytes aedon). American Naturalist 150:650-661.
Oliarnyk, C. J. 1996. Habitat selection and reproductive success in a population of
Cerulean Warblers in southeastern Ontario. M.S. Thesis, Queen’s University,
Kingston, Ontario, Canada.
6
Oliarnyk, C. J. and R. J. Robertson. 1996. Breeding behavior and reproductive success of
Cerulean Warblers in Southeastern Ontario. Wilson Bulletin 108:673-684.
Pärt, T., Arlt, D., and Villard, M-.A. 2007. Empirical evidence for ecological traps: a twostep model focusing on individual decisions. Journal of Ornithology 148:S327
S332.
Sauer, J. R., J. E. Hines and J. Fallon. [online]. 2008. The North American Breeding Bird
Survey,Results and Analysis 1966-2007 version 5.15,2008. USGS Patuxent
Wildlife Research Center, Laurel, Maryland, USA.
Wilcove, D. S. 1985. Nest predation in forest tracts and the decline of migratory
songbirds. Ecology 66:1211–1214.
-Chapter 1Forest Management Effects on Cerulean Warbler Territory Size in Southern Indiana
Ryan H. Dibala
8
Abstract
I studied the effects of silviculture treatments on territory sizes of the Indiana
state-endangered Cerulean Warbler (Setophaga cerulea) in Morgan-Monroe and
Yellowwood state forests in southern Indiana. Uneven and even-aged harvests were
implemented in the fall of 2008 across six of nine managements units; three control
sites received no treatment. I hypothesized that silviculture treatments would result in
an increase in territory size to account for loss of forest cover. Cerulean Warblers were
detected and territory sizes were recorded during the summers of 2010 and 2011. A
general linear model showed that there were no differences in mean territory size
between pre- and post-harvest years. When analyzed at the treatment level over all five
years, a one-way ANOVA showed that even-aged areas had territory mean sizes that
were significantly smaller than territories in control areas (F2,341 = 3.39, p = 0.035) but
territory means in uneven-aged areas were not significantly different from mean
territory sizes in either control or even-aged areas. Additionally, mean number of
territories in even-aged areas was significantly greater than in control areas (F2, 41 = 5.82,
p = 0.006). Territory density was highest in even-aged units, suggesting that Cerulean
Warblers are attracted to these areas.
Keywords: Cerulean Warbler, Setophaga cerulea, even-aged silviculture, territory size.
9
Introduction
In the wake of human population growth and overuse of natural resources,
conservationists have devoted exceedingly greater research efforts to forest
conservation and management at local and global levels. Timber harvesting, in
particular, has had noticeable effects on forest community assemblages and alternative
silviculture practices have been shown to both benefit and detract from the needs of
forest songbirds (Thompson III et al. 1993). One area-sensitive and forest-dependent
songbird, the Cerulean Warbler (Setophaga cerulea), has received recent attention
because it is especially sensitive to ongoing forest fragmentation and isolation (Robbins
et al. 1992).
The Cerulean Warbler is a Nearctic-Neotropical migrant songbird that breeds in
mature deciduous forests of eastern and central North America and winters on the
Andean slopes of northwestern South America (Hamel 2000). Over the past five
decades, numbers of Cerulean Warblers have declined precipitously. According to the
North American Breeding Bird Survey, there has been an annual population decline of
4.1% between 1966 and 2007 (Sauer et al. 2008). Populations are estimated to have
dropped approximately 70% since 1966 and now are experiencing the greatest decline
of any North American wood warbler (Sauer et al. 2008). This decline is so alarming that
the species has been listed as a species of conservation concern by the U.S. Fish and
Wildlife Service (U.S. Fish and Wildlife Service 2008) and has been declared as
“vulnerable”on the International Union for the Conservation of Nature’s (IUCN) red list
10
(Birdlife International 2004). The reason for this population decline has been attributed
to loss of contiguous forest cover and habitat fragmentation throughout its range
(Hamel 2000). These alterations often play host to more insidious threats such as
increased brood parasitism and exposure to predators on breeding grounds (Bakermans
and Rodewald 2009). Also, survival and return rates from their wintering grounds could
be a limiting factor, but little has been published about Cerulean Warbler non-breeding
ecology (Robbins et al. 1992, Jones et al. 2000).
Cerulean Warblers are an area-sensitive species that depend on large,
contiguous blocks of mature deciduous forest and tall trees for successful breeding
(Hamel 2000). Several studies have compared vegetative components within territories
and non-use sites to identify habitat characteristics that are attractive to Cerulean
Warblers. It appears that a heterogeneous, three-dimensional structure of the canopy
within the forest is an important landscape feature for this species (Lynch 1981, Hamel
2000, Jones et al. 2001). In Southern Indiana, Cerulean Warbler territories were
associated with a tall canopy, high percentage of canopy cover, steep slope, and trees
with a DBH ≥38 cm. Additionally, nest sites and territories were associated with Virginia
creeper (Parthenocissus quinquefolia) and grape vine (Vitis sp.), respectively (Roth and
Islam 2008). Kaminski (2010) found that Cerulean Warbler territories were
approximately 153.3 m closer to small conifer patches than non-use sites. Some authors
have suggested that Cerulean Warblers may be attracted to canopy gaps or openings
and these gaps may be an important aspect of nest-site selection (Bent 1953, Oliarnyk
11
1996, Oliarnyk and Robertson 1996). Conversely, there has been concern that too many
openings within a forest’s interior could maximize edge-effects and internally fragment
what once was continuous forest (Annand and Thompson 1997).
Hamel (2000) identified the response of populations to land management
activities as a high-priority research need for Cerulean Warblers. Since then, studies
have focused on the negative effects of abrupt habitat change associated with
mountaintop removal mining in West Virginia (Wood et al. 2005a), large-scale landscape
disturbance events (Jones et al. 2001), and the effects of silviculture treatments
(Register and Islam 2008, Wood et al. 2005b, Bakermans and Rodewald 2009). Hamel et
al. (2004) further identified studying the effects of silviculture treatments on the
occurrence of this species as a pressing research need. Silviculture practices commonly
used in North America can be grouped into one of two classifications: even-aged and
uneven-aged management (Thompson III et al. 1993). Even-aged stands are
characterized by trees that are the same age class throughout and are maintained by
techniques such as clear-cutting and shelterwood. Clear-cutting involves removal of the
entire stand (<1 ha to >100 ha) in one cutting, whereas shelterwood requires the
gradual removal of the entire stand in a series of partial cuttings (Thompson III et al.
1993). Uneven-aged stands are single trees or groups of trees that are periodically
harvested, creating a multi-age-class forest. Selection methods such as single tree
removal and patch cutting create small gaps and are used to promote regeneration of
shade-tolerant tree species.
12
Selectively cut stands typically retain much of the forest bird community, but
their numbers are often lower (Thompson III et al. 1993). Moreover, several studies
have provided evidence that uneven-aged forest management has fewer negative
effects than even-aged management on area-sensitive songbirds (Oliarnyk and
Robertson 1996, Jones and Robertson 2001, Weakland and Wood 2005, Roth and Islam
2008, Register and Islam 2008). It is likely that uneven-aged treatments such as single
tree removal mimic canopy gaps and openings that naturally occur in mature forests
(Flashpohler 1993).
In an attempt to better understand the effects of forest management practices
on native plants and animals of Indiana, a consortium of state agencies and Universities
initiated a 100-year study known as the Hardwood Ecosystem Experiment (HEE).
Launched in 2006, the project encompasses nine management units (~282-363 ha) in
Yellowwood and Morgan-Monroe state forests in Southern Indiana that provide an
exceptional opportunity for the study of silviculture treatments and their effects on
native wildlife and plant regeneration. Uneven and even-aged harvests were
implemented in the fall of 2008 across six of nine managements units; three control
sites received no treatment. Control units were left unharvested, while uneven-aged
units were treated with single tree and patch cut harvests, and even-aged units were
treated with shelterwood and clear-cut harvests (HEE online).
Cerulean Warblers were studied on the HEE management units in Southern
Indiana to determine if and how silviculture treatments are affecting this population.
13
Specifically, this study examined changes in territory size and number among even-aged,
uneven-aged, and control units between pre- and post-harvest years. Vegetation
structure was also compared among territories and randomly selected non-use areas.
Forest harvesting began in late summer 2008 and lasted until early April 2009. I
hypothesized that the total number of territories would decrease significantly after the
harvest and that the size of territories would increase due to reduced conspecific
competition. Lastly, I predicted that territories would have significantly larger tree
diameters, steeper slope, and be closer to streams and roads than non-use areas.
Materials and Methods
Background
Research was conducted in nine management units established by the HEE
project in Brown, Morgan, and Monroe counties of Southern Indiana (Figure 1). Four
units were located in Morgan-Monroe and five units in Yellowwood state forests.
Uneven-aged units were comprised of four 0.4 ha, two 1.2 ha, and two 2 ha openings
(group cuts) and several small patch cuts with a target basal area of 16.1 – 23.0 m²/ha
(Figure 2). Even-aged units had four openings (two shelterwoods and two clearcuts)
each a total of 4 ha (Figure 3). Shelterwood cuts removed a range of 45-53 m²/ha in
canopy cover and will be re-harvested after understory regeneration is complete
(unknown date). All control units received no harvest and were used to monitor
Cerulean Warblers in the absence of forest management (Figure 4). Harvests occurred
14
on slopes in each of the four cardinal directions (HEE online). Habitat consisted of oakhickory deciduous forest with steep drainages, rolling hills, and ephemeral creeks. The
study site lies within the largest block of contiguous forest in Southern Indiana and fits
descriptions of quality Cerulean Warbler habitat.
I collected data on territory size in the spring and summer of 2010 and 2011.
These data were compared with two years of pre-harvest data (2007 and 2008) and one
year of post-harvest data (2009) from Prichard’s (2007) study and Kaminski (2010) and
MacNeil’s (2010) theses. These data provide long-term, baseline information regarding
Cerulean Warbler population response to forest harvesting.
Point Count Surveys
One hundred-meter fixed radius point count surveys were conducted
throughout the month of May to locate singing males who were establishing territories.
Surveys were conducted within a 259 ha sample grid consisting of 49 bird survey points
(7x7; 1.96 km2 with a 50 m forest buffer). These points were arranged in seven northsouth transect lines where there was a 200 m distance between each point to rule out
the possibility of dual detection (Jones et al. 2000, Hamel et al. 2009). Surveys were
conducted between 05:30 and 10:30 EST and none took place on windy or rainy days.
One point count was conducted for each survey point and lasted five minutes. The first
two minutes were spent listening for singing males. This was followed by one minute of
Cerulean Warbler song broadcasting via an MP3 player with an external speaker to elicit
15
a vocal response from any males in the immediate area. The last two minutes were
again spent listening without playback (Falls 1981). When a bird was detected, its
approximate distance from the point and compass direction were recorded.
Territory Delineation
Points where birds were initially heard were revisited to delineate territory
boundaries. Male Cerulean Warblers were located by their incessant singing, and trees
in which birds sang repetitively were identified to species and marked with flagging
tape. A Garmin 76 handheld Global Positioning System (GPS) unit was used to mark the
location of the tree in a Universal Transverse Mercator (UTM) coordinate system. A
territory was considered complete when between 5 and 12 trees were recorded for an
individual. Territory locations and sizes were determined by creating minimum convex
polygons in ArcMap (ArcGIS 10).
Vegetation Sampling
Vegetation sampling began at the beginning of July when detection proved
difficult due to a substantial decrease in singing rate. Sampling was conducted at the
center of each territory where a 0.04 ha circular plot was marked. Using the methods of
James and Shugart (1970), aspect was assessed at the plot’s origin and slope was
measured with a clinometer in each cardinal direction. Presence and absence of canopy
and ground cover were recorded with a GRS densitometer at 2 m intervals along each
cardinal direction of the plot. Woody plants with a diameter at breast height (DBH) ≤3
16
cm and 3-10 cm were identified to species within a 5 m radius of the plot’s center. In
each quadrant, mature trees (>10 cm DBH), both living and dead, were identified to
species and a rangefinder was used to measure maximum canopy height in each
quadrant.
GIS Analysis
A geodatabase was created in ArcMap (ArcGIS 10) to display and analyze all
geospatial data. UTM coordinates were imported to ArcMap and polygons were
constructed in a two-step process: 1) triangular irregular networks (TINs) were created
to display third dimension attributes in vector format and 2) an attribute domain was
then created to ensure data integrity. Each domain represents a separate territory and
includes information about the shape’s length and area. Domains were added to a
larger feature class depending on their make-up. For example, separate feature classes
were created for territories and non-use areas for multiple years. These layers were
superimposed onto GIS layers of the nine management units with associated landscape
features and harvest areas. These, along with raster data such as aerial photographs
and a digital elevation model (DEM) were obtained from the Indiana Spatial Data Portal
(Kaminski 2010). These files were used to analyze differences in elevation, slope, and
aspect of Cerulean Warbler territories that were derived from the vector polygons using
the zonal statistics tool under Zonal in Spatial Analyst Tools.
17
Territory centroids were created for polygon feature classes using the feature to
point tool. Distances were measured to and from the centroids of polygon features by
generating a Near Table under Proximity in Analysis Tools.
Statistical Analyses
A general linear model (GLM) was used to test for post-harvest changes in
territory size and number among the treatments and a subsequent one-way Analysis of
Variance (ANOVA) was used to test for differences between silviculture treatments.
Two-sample t-tests were used to test for differences between territories and non-use
areas in spatial attributes such as distances to landscape features, slope, aspect, and
elevation. I investigated whether there were any differences in vegetative
characteristics between territories and random non-use areas by using Multivariate
Analysis of Variance (MANOVA, Sharma 1996). Following significant multivariate results,
I examined each response variable separately using a one-way ANOVA in order to
determine which variable(s) were statistically significant. Bonferroni adjustments were
made for all multiple comparisons of variables that were not considered independent.
All tests were performed with Minitab (Version 16) at α = 0.05.
All data were checked for normality and non-normal data were log-transformed.
In cases where the data were extremely positively skewed, the non-parametric MannWhitney U-test was used because of its higher power in these situations (LeBlanc
18
personal communication). Therefore, median values are presented occasionally
throughout.
Results
I detected a total of 93 male Cerulean Warblers in 2010 and 130 in 2011 (Table
1). Of these total detections, 50 territories in 2010 and 101 in 2011 were demarcated.
This compares to the 65, 55, and 76 territories demarcated in 2007 (Prichard Young
2007), 2008, and 2009, respectively (Kaminski 2010, MacNeil 2010). There was no
difference in the mean number of territories between pre- and post-harvest years (F1, 40
= 0.11, p = 0.741, log transformed) but there was a significant difference among
treatment groups (F2, 40 = 5.65, p = .007, log transformed). A subsequent ANOVA was
used to test for differences in number of territories among experimental units over all
five years and a post-hoc Tukey’s HSD test determined that mean number of territories
in even-aged areas was significantly greater than in control areas (F2, 41 = 5.82, p = 0.006)
but mean number of territories in uneven-aged areas was not significantly different
from control or even-aged areas (Figure 5).
Territory sizes ranged from 0.01 ha to 1.75 ha, with an overall mean of 0.28 ha
(Table 2, see Appendix III). There was no difference in mean territory size between preand post-harvest years (F1, 340 = 1.87, p = 0.173, Figure 6) but a significant difference
existed among treatment groups (F2, 340 = 3.56, p = .029). A subsequent ANOVA was
used to test for differences in mean territory size among experimental units over all five
19
years and a post-hoc Tukey’s HSD test determined that even-aged areas had territory
mean sizes that were significantly smaller than territories in control areas (F2, 341 = 3.39,
p = 0.035) but territory means in uneven-aged areas were not significantly different
from mean territory sizes in either control or even-aged areas (Figure 7).
Results of the MANOVA indicated that use and non-use areas differed
significantly with respect to two vegetative habitat characteristics (Wilks’ λ, F11,191 =
6.416, p < 0.001). Subsequent ANOVAs (Table 3) with Bonferroni adjustments showed
that territories had significantly more woody species between 0 and 3 cm DBH (p =
0.028), than non-use areas. Alternatively, non-use areas had significantly more woody
species between 3 and 10 cm DBH than territories (p = 0.001, Table 4).
When Cerulean Warbler territories were compared to random non-use areas, I
found that the median distance to streams was significantly shorter for territories than
it was for non-use areas (p ˂0.001, Mann-Whitney U-test). These data also suggest that
there is a significant difference in median distance to roads between use sites and nonuse sites (p = 0.074, Mann-Whitney U-test). Territories were significantly closer to
conifer patches than non-use sites (p˂0.001, Mann-Whitney U-test) and there was no
difference found in median distance to harvest areas (p = 0.277, Mann-Whitney U-test,
Table 4). Surprisingly, there was no difference in median slope (p = 0.522; MannWhitney U-test) although there was a significant difference in median aspect between
territories and non-use sites (p˂0.001, Mann-Whitney U-test), showing that Cerulean
Warblers preferred eastern facing slopes (109.47° E/SE). Finally, the data suggest that
20
there is a difference in mean elevation between use and non-use sites (t = -1.79, p =
0.075, 2-sample t-test). Territories appear to be located at lower elevations than nonuse sites. All significant differences remained significant after Bonferroni corrections
were made.
Discussion
Territory sizes were smaller than those presented by Oliarnyk (1996) who
showed that territories in Southern Ontario ranged in size from 0.38 ha to 2.4 ha.
However, Robbins et al. (1992) noted that territories smaller than 0.38 ha are possible.
In fact, mean territory size of 51 Cerulean Warbler territories demarcated at Big Oaks
National Wildlife Refuge in Southern Indiana was 0.21 ha (Islam and Roth 2004).
Furthermore, previous research on Cerulean Warblers in the Hoosier National Forest,
Yellowwood State Forest, and Morgan-Monroe state forest documented a range in size
from 0.04 ha to 1.43 ha, with a mean of 0.34 ha (Islam and Basile 2002).
Data presented here show that there was no significant change in territory size
or number post-harvest, rejecting my hypothesis. My prediction that the even-aged
harvest would reduce the number of birds, alleviating competition and making
territories larger was not supported. Instead, when all five years were compared
disregarding the harvest, even-aged units contained a greater number of territories with
smaller sizes than control sites.
21
Cerulean Warblers appear to be settling in and using areas close to canopy gaps
in these forests. My results show that these birds are settling closer to streams and
roads, two landscape features that create small canopy openings in the forest. These
findings support previous studies claiming that Cerulean Warblers are associated with
canopy gaps (Wood et al. 2005b, Oliarnyk and Robertson 1996, Hamel 2000). Territory
placement closer to conifer patches was confirmed, supporting the findings of Kaminski
(2010). Because there is no other indication of this species using coniferous habitats in
the literature, my interpretation is that there is a correlation between planted conifer
patches and streams and it is the latter feature that attracts this species. This reasoning
can be used in the interpretation of finding Cerulean Warbler territories at lower
elevations at the bottom of ravines where streams are most prevalent.
Similar to previous studies, aspect was shown to influence Cerulean Warbler
settlement, with principal use of eastern facing slopes (Wood et al. 2005b, Kaminski
2010). Other research suggests that forest growth in the northern hemisphere is
frequently greatest on north-to-east-facing slopes (Beers et al. 1966). Several studies
have found that Cerulean Warbler males perch in trees with diameters that are
significantly larger than average trees available to them in their territories (Robbins et
al. 1992, Jones and Islam 2006). Larger trees and greater structural diversity on eastern
aspects could provide Cerulean Warblers with ideal song perch posts. Surprisingly, I did
not find any differences in slope between territories and non-use areas. This contrasts
22
from the findings of other studies (Roth and Islam 2007, Kaminski 2010, Buehler et al.
2008).
Although not significant, most pronounced increases in number of territories
post-harvest occurred in even-aged areas. It is possible that Cerulean Warblers are
selecting habitat based on within-territory characteristics and are not negatively
affected by harvests in surrounding areas of the forest. In West Virginia, Cerulean
Warbler abundance in unharvested stands directly adjacent to clear-cut and two-age
treatments (gradual removal of stand) was similar to that in unharvested control stands
away from the cuts (Wood et al. 2005b). In Southern Ohio, Bakermans and Rodewald
(2009) examined nest success in relation to adjacency of regenerating clear-cuts and
found that variation in local habitat (within territory) features played more of a role in
nest productivity than the nearness or size of the clearcuts. Furthermore, the
regenerating systems did not contribute significantly to edge-related nest predation
events. They concluded that there is no evidence that Cerulean Warblers are sensitive
to intensive timber harvesting in the immediate landscape surrounding mature forest
sites (Bakermans and Rodewald 2009).
Cerulean Warblers may find something attractive about even-aged units and
settle in them because of it. Boves (2011) found that Cerulean Warbler territory density
was highest after intermediate and heavy disturbance, suggesting that this species may
seek out habitat altered by large-scale disruptions like fire or landslides rather than
23
single tree-fall gaps. Additionally, he found that males occupying disturbed areas had
greater body mass (better body condition) than those in control areas (Boves 2011).
Even-aged areas promote the succession of small woody species, a variable that
seems to be important in Cerulean Warbler habitat selection. Dense woody understory
that colonizes clearcuts has been shown to provide protection from predators and food
resources for mature forest birds during the post-fledging period (Marshall et al. 2003,
Vitz and Rodewald 2006). I observed both male and female Cerulean Warblers foraging
in smaller trees on the edges of clearcuts as well as fledglings being led by adults
through thick, woody understory in even-aged plots. In one of the management units,
the largest aggregation of birds was located directly within a shelterwood cut (Figure 8).
Several studies have shown that breeding bird abundance and diversity increases in
two-age stands (shelterwoods) and that they are attractive to many late-successional
forest species (Boardman and Yahner 1999, Duguay et al. 2001). A study on songbird
nest survival rates in West Virginia concluded that two-age treatments placed within
extensively forested areas do not result in the type of edge effects (population sinks)
observed in areas fragmented by agriculture. Two-age treatments can also provide a
more aesthetic and viable conservation alternative to clearcutting where brood
parasitism is not a concern (Duguay et al. 2001). McDermott and Wood (2009) found
that 19-26 year-old two-age harvests were beginning to provide habitat for some
species of mature forest songbirds that were absent or uncommon previously.
Conclusions and Management Recommendations
24
Cerulean Warblers occur in greater numbers with smaller territory sizes in evenaged management units throughout Morgan-Monroe and Yellowwood state forests.
Despite appearing benign or even beneficial, it would be dangerous to speculate that
even-aged silviculture could be used in future management efforts for this species
without accounting for survival or reproduction. The assessment of logging effects by
measuring bird populations in the absence of measurements of effects on reproductive
success can be misleading (Brawn and Robinson 1996, Van Horne 1983). Therefore, it is
essential that future research continues to monitor Cerulean Warbler fecundity in and
near the harvests to more effectively determine the long-term consequences of evenaged silviculture.
Songbirds have a tendency to exhibit a lag response to habitat disturbance
(Brooks et al. 1999) and it is possible that large clearcuts and shelterwood harvests
could be associated with more insidious threats that are not immediately perceived.
Many species of birds have been shown to be attracted to areas where they experience
poor survival or reproductive success, especially in human-altered landscapes (Gates
and Gysel 1978, Wilcove 1985). In the Appalachian Mountains, Boves (2011) found that
although Cerulean Warbler territory density and body condition was highest after
intermediate and heavy forest disturbance, reproductive success was significantly lower.
Cerulean Warblers in Yellowwood and Morgan-Monroe state forests had lower
reproductive success in both even and uneven-aged areas than control areas (Wagner
25
unpublished data). Even-aged areas could be serving as ecological traps that could
ultimately have a negative impact on the population (Pärt et al. 2007, Boves 2011).
Even-aged silviculture may have different effects on Cerulean Warbler
reproduction and survival in different landscapes. The HEE treatments removed a total
of 75.7 ha of timber, meaning that only 6.43% of the forest within the six treated sites
was harvested (Kaminski 2010). This is a relatively small-scale harvest, but it was done
in two state forests that lie within the highly fragmented agricultural Midwest. Similar
harvests in more contiguously forested habitats may contribute to greater reproductive
success in those areas.
26
Literature Cited
Annand, E. M. and F. R. Thompson III. 1997. Forest bird response to regeneration
practices in central hardwood forests. Journal of Wildlife Management 61:159
171.
Bakermans, M. H. and A. D. Rodewald. 2009. Think globally, manage locally: The
importance of steady-state forest features for a declining songbird. Forest
Ecology and Management 258:224-232.
Beers, T. W., P. E. Dress, and L. C. Wensel. 1966. Notes and observations. Aspect
transformation in site productivity research. Journal of Forestry 64:691-692.
Bent, A. C. 1953. Life Histories of North American Wood Warblers, parts I and II. Dover
Publications, New York.
Birdlife International. 2004. Threatened Birds of the World. CD-ROM. Birdlife
International, Cambridge, UK.
Boardman, L. A., and R. H. Yahner. 1999. Wildlife communities associated with even
aged reproduction stands in two state forests of Pennsylvania. Northern Journal
of Applied Forestry 16:89-95.
Boves, T. J. 2011. Multiple responses by Cerulean Warblers to experimental forest
disturbance in the Appalachian Mountains. PhD dissertation, University of
Tennessee, Knoxville, TN.
Brawn, J. D. and S. K. Robinson. 1996. Source-sink population dynamics may complicate
the interpretation of long-term census data. Ecology 77:3-12.
Brooks, T. M., S. L. Pimm, and J. O. Oyugi. 1999. Time lags between deforestation and
bird extinction in tropical forest fragments. Conservation Biology 13:1140-1150.
Buehler, D. A., J. J. Giocomo, J. Jones, P. B. Hamel, C. M. Rogers, T. A. Beachy, D. W.
Varble, C .P. Nicholson, K. L. Roth., J. Barg, R. J. Robertson, J. R. Robb, and K.
Islam. 2008. Cerulean Warbler Reproduction, Survival, and Models of
Population Decline. Journal of Wildlife Management 72:646-653.
Duguay, J. P., P. B. Wood, and J. V. Nichols. 2001. Songbird Abundance and Avian Nest
Survival Rates in Forests Fragmented by Different Silvicultural Treatments.
Conservation Biology 15:1405-1415.
Falls, J. B. 1981. Mapping territories with playback: an accurate census method for
songbirds. Studies in Avian Biology 6:86-91.
27
Flaspohler, D. J. 1993. Wisconsin Cerulean Warbler Recovery Plan. Bureau of
Endangered Resources Technical Publication #96. Wisconsin Department of
Natural Resources, Madison, WI.
Hamel, P. B. 2000. Cerulean Warbler (Dendroica cerulea). The Birds of North America,
No. 511 (A. Poole and F. Gill, eds.). The Birds of North America, Inc.,
Philadelphia, PA.
Hamel, P. B., D. K. Dawson, and P. D. Keyser. 2004. How we can learn more about the
Cerulean Warbler (Dendroica cerulea). Auk 121:7-14.
Hamel, P. B., M. J. Welton, C. G. Smith, III, and R. P. Ford. 2009. Test of Partners in
Flight effective detection distance for cerulean warbler. Pp. 328–333 in Rich, T.
D., C. Arizmendi, D. W. Demarest, and C. Thompson (eds). Tundra to tropics:
connecting birds, habitats, and people. Proceedings of the 4th international
Partners in Flight conference 13-16 February 2008, McAllen, TX.
Hardwood Ecosystem Experiment. Online
http://www.fnr.purdue.edu/HEE/Overview/Overview.htm
Islam, K., and C. Basile. 2002. Relative abundance and habitat selection of Cerulean
Warblers in Southern Indiana. Final report submitted to U.S. Fish and Wildlife
Service, Fort Snelling, MN, December 2002. Department of Biology Technical
Report No. 1, Ball State University, Muncie, Indiana 76 pp.
Islam, K., and K. L. Roth. 2004. Habitat Selection and Reproductive Success of Cerulean
Warblers in Southern Indiana. Final report submitted to U.S. Fish & Wildlife
Service, Fort Snelling, MN, December 2004. Department of Biology Technical
Report No. 4, Ball State University, Muncie, Indiana 51 pp.
James, F. C. and H. H. Shugart. 1970. A Quantitative Method of Habitat Description.
Audubon Field Notes 24:727-736.
Jones, J., P. Ramoni-Perazzi, E. H. Carruthers, and R. J. Robertson. 2000. Sociality and
foraging behavior of the Cerulean Warbler in Venezuelan shade coffee
plantations. Condor 102:958-962.
Jones, J., R. D. DeBruyn, J. J. Barg, and R. J. Robertson. 2001. Assessing the effects of
natural disturbance on a Neotropical migrant songbird. Ecology 82:2628– 2635.
Jones, J. and R. J. Robertson. 2001. Territory and nest-site selection of Cerulean
Warblers in eastern Ontario. Auk 118:727-735.
Jones, K. and K. Islam. 2006. Selection of song perches by Cerulean Warblers.
Proceedings of the Indiana Academy of Science 115:37-43.
28
Kaminski, K. J. 2010. Cerulean Warbler Initial Response to Silviculture Treatments in
Southern Indiana. M.S. Thesis, Ball State University, Muncie, IN.
LeBlanc, D., 2008. Statistics: concepts and applications for science. XanEdu Publishers,
Michigan.
Lynch, J.M. 1981. Status of the cerulean warbler in the Roanoke River basin of North
Carolina. Chat 45, 29-35.
MacNeil, M. 2010. Does timber harvesting affect Cerulean Warbler foraging ecology?
M.S. Thesis, Ball State University, Muncie, IN.
Marshall, M. R., J. A. Dececco, A. B. Williams, G. A. Gale, and R. J. Cooper. 2003. Use of
regenerating clearcuts by late-successional bird species and their young during
the post-fledging period. Forest Ecology and Management 183:127-135.
McDermott, M. E., and P. B. Wood. 2009. Short and long-term implications of clearcut
and 2-age silviculture for conservation of breeding forest birds in the central
Appalachians, USA. Biological Conservation 142:212-220.
Oliarnyk, C. J. 1996. Habitat selection and reproductive success in a population of
Cerulean Warblers in southeastern Ontario. M.S. Thesis, Queen’s University,
Kingston, Ontario, Canada.
Oliarnyk, C. J. and R. J. Robertson. 1996. Breeding behavior and reproductive success of
Cerulean Warblers in Southeastern Ontario. Wilson Bulletin 108:673-684.
Pärt, T., Arlt, D., and Villard, M-.A. 2007. Empirical evidence for ecological traps: a twostep model focusing on individual decisions. Journal of Ornithology 148:S327
S332.
Register, S. M. and K. Islam. 2008. Effects of Silvicultural Treatments on Cerulean
Warbler (Dendroica cerulea) Abundance in Southern Indiana. Forest Ecology and
Management 255:3502-3505.
Robbins, C. S., J. W. Fitzpatrick, and P. B. Hamel. 1992. A warbler in trouble: Dendroica
cerulea. In: Ecology of Conservation of Neotropical Migrant Landbirds.
Smithsonian Institution Press, Washington DC, pp. 549-562.
Roth, K. L. and K. Islam. 2008. Habitat Selection and Reproductive Success of Cerulean
Warblers in Indiana. Wilson Journal of Ornithology 120:105-110.
Sauer, J. R., J. E. Hines and J. Fallon. [online]. 2008. The North American Breeding Bird
Survey,Results and Analysis 1966-2007 version 5.15,2008. USGS Patuxent
Wildlife Research Center, Laurel, Maryland, USA.
29
Sharma, S. 1996. Applied Multivariate Techniques. John Wiley and Sons, Inc., New
York.
Thompson, F. R., J. R. Probst, and M. G. Raphael. 1993. Silvicultural options for
Neotropical migratory birds. In: D. M. Finch, P. W. Stangel, (eds.). Status and
management of neotropical migratory birds: September 21-25, 1992, Estes Park,
Colorado. General Technical Report RM-229. Fort Collins, CO: Rocky
Mountain Forest and Range Experiment Station, U.S. Dept. of Agriculture, Forest
Service:353-362.
U.S. Fish and Wildlife Service. 2008. Birds of conservation concern. United States
Department of Interior, Fish and Wildlife Service, Division of Migratory Bird
Management, Arlington, VA, USA.
Van Horne, B. 1983. Density as a misleading indicator of habitat quality. Journal of
Wildlife Management 47:893-901.
Vitz, A. C., and A. D. Rodewald. 2006. Can regenerating clearcuts benefit mature-forest
songbirds? An examination of post-breeding ecology. Biological Conservation
127:477-486.
Weakland, C.A. and P. B. Wood. 2005. Cerulean Warbler (Dendroica cerulea)
microhabitat and landscape level habitat characteristics in southern West
Virginia. Auk 122:497-508.
Wood, P. B., S. B. Bosworth, and R. Dettmers. 2005a. Cerulean Warbler abundance and
occurrence relative to large-scale edge affect habitat characteristics. Condor
108:154-165.
Wood, P. B., J. P. Duguay, and J. V. Nichols. 2005b. Cerulean warbler use of
regenerated clear-cut and two-age harvests. Wildlife Society Bulletin 33:851
858.
Young, L. C. 2007. Distribution and foraging ecology of Cerulean Warblers in Southern
Indiana. M.A. Thesis, Ball State University, Muncie, IN.
30
©Cortney Mycroft 2008
Figure 1. Hardwood Ecosystem Experiment (HEE) management units used to study
Cerulean Warblers in Yellowwood and Morgan-Monroe state forests in Southern
Indiana.
31
Figure 2. Cerulean Warbler territories and random vegetation plots mapped in 2010 and
2011 in an uneven-aged unit (Unit 7) within Yellowwood state forest in Southern
Indiana.
32
Figure 3. Cerulean Warbler territories and random vegetation plots mapped in 2010 and
2011 in an even-aged unit (Unit 3) within Morgan-Monroe state forest in Southern
Indiana.
33
Figure 4. Cerulean Warbler territories and random vegetation plots mapped in 2010
and 2011 in a control unit (Unit 5) within Yellowwood state forest in Southern Indiana.
34
Territory Number Among Experimental Units
1.6
Log Territory Number
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Control
Even
Experimental Unit
Uneven
Figure 5: Number of Cerulean Warbler territories on a logarithmic scale among all three
experimental units at Yellowwood and Morgan-Monroe state forests in Southern
Indiana. Over all five years, even-aged units had significantly more territories than
control units but did not differ significantly from uneven-aged units.
35
Territory Size in Even-aged Units
Log Territory Size (ha)
0.0
-0.5
-1.0
-1.5
-2.0
Pre
Post
Figure 6. Cerulean Warbler territory sizes on a logarithmic scale of even-aged units preand post-harvest at Yellowwood and Morgan-Monroe state forests in Southern Indiana.
Despite the significant increase in the number of territories (Figure 5), territory size did
not decrease significantly.
36
Territory Sizes Among Experimental Units
Log Territory Size (ha)
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
Control
Even
Experimental Unit
Uneven
Figure 7. Cerulean Warbler territory sizes on a logarithmic scale among all three
experimental units at Yellowwood and Morgan-Monroe state forests in Southern
Indiana. Territories in even-aged units were significantly smaller than control units but
did not differ significantly from uneven-aged units.
37
Figure 8. Cerulean Warbler territories demarcated in 2010 and 2011 aggregated near a
shelterwood cut in Unit 9 at Yellowwood state forest in Southern Indiana.
38
Table 1. Numbers of Cerulean Warblers detected in 2010 and 2011 in Yellowwood and Morgan-Monroe state forests in Southern
Indiana. Notice that Units 3 and 8 consistently have greater numbers of birds than other units. R.A. = Relative Abundance.
Harvest Type
Control
Control
Control
Total
Even-aged
Even-aged
Even-aged
Total
Uneven-aged
Uneven-aged
Uneven-aged
Total
Total
Unit #
2
4
5
3
3
6
9
3
1
7
8
3
9
2010
5
3
7
15
22
13
16
51
1
8
18
27
93
R.A.
2.55
1.53
3.57
2.55
11.22
6.63
8.16
8.67
0.51
4.08
9.18
4.59
2011
7
8
19
34
19
26
11
56
1
10
29
40
130
R.A.
3.57
4.08
9.69
5.78
9.69
13.27
5.61
9.52
0.51
5.1
14.8
6.8
39
Table 2. Number of Cerulean Warbler territories and their mean sizes from pre-harvest years (2007-2008) and post-harvest
years (2009-2011) at Yellowwood and Morgan-Monroe state forests in Southern Indiana. Values are presented as the mean ± 1
SD. Terr. = Territories.
Harvest
Site
2007 (# of terr.) Area (ha) 2008 (# of terr.) Area (ha) 2009 (# of terr.) Area (ha) 2010 (# of terr.) Area (ha) 2011 (# of terr.) Area (ha)
Uneven
1
7
8
0
7
24
0
0.18 ± 0.08
0.18 ± 0.17
1
7
21
0.44 ± 0
0.86 ± 0.59
0.19 ± 0.10
0
6
26
0
0.37 ± 0.26
0.22 ± 0.21
0
3
16
0
0.14 ± 0.05
0.25 ± 0.33
0
6
31
0
0.38 ± 0.27
0.20 ± 0.14
Even
3
6
9
8
6
9
0.18 ± 0.14
0.16 ± 0.15
0.13 ± 0.13
13
0
5
0.28 ± 0.16
0
0.31 ± 0.27
21
6
7
0.17 ± 0.23
0.26 ± 0.24
0.09 ± 0.03
16
5
14
0.16 ± 0.10
0.27 ± 0.21
0.15 ± 0.15
13
14
13
0.20 ± 0.22
0.16 ± 0.19
0.23 ± 0.26
Control
2
4
5
1
4
6
0.11 ± 0
0.4 ± 0.46
0.11 ± 0.07
3
2
3
0.4 ± 0.11
0.44 ± 0.04
0.69 ± 0.24
0
3
7
0
0.19 ± 0.11
0.24 ± 0.14
2
0
2
0.38 ± 0.05
0
0.37 ± 0.05
2
10
12
0.59 ± 0.49
0.33 ± 0.25
0.16 ± 0.15
Total:
65
55
Summary Statistics
Variable
2007
2008
2009
2010
2011
N
65
55
76
58
101
Mean SE Mean
0.1774 0.0236
0.3628 0.0462
0.2102 0.0251
0.2046 0.0287
0.2276 0.0226
StDev Minimum Maximum
0.1899 0.0147
1.1827
0.3426 0.0190
1.7513
0.2186 0.0197
0.8867
0.2187 0.0032
1.2076
0.2266
0.0067
1.0813
76
58
101
40
Table 3. Results of ANOVAs that examined how vegetative characteristics differed between Cerulean Warbler use and non-use
sites in Yellowwood and Morgan-Monroe state forests in Southern Indiana. Highlighted cells show F and p-values that were
considered significant after Bonferroni adjustments were made. Values are presented as the mean ± 1 SD.
Response variable
Canopy height
Number of woody species
Species of woody species
Number of woody species (0-3 cm)
Number of woody species (3-10 cm)
Number of trees
Species of trees
Tree diameter at breast height (DBH)
ANOVA
Mean (use) Mean (non-use)
0.83 (0.365) 24.03 ± 3.82
24.47 ± 3.70
5.16 (0.024) 26.57 ± 17.11
21.5 ± 14.38
4.87 (0.028)
5.74 ± 2.53
4.99 ± 2.23
8.35 (0.004) 24.02 ± 17.28
17.63 ± 13.81
11.14 (0.001)
2.55 ± 2.5
3.88 ± 3.14
4.29 (0.040) 12.10 ± 4.58
13.42 ± 4.43
2.07 (0.152)
5.51 ± 2.02
5.14 ± 1.70
0.25 (0.615) 28.25 ± 5.71
27.87 ± 5.01
41
Table 4. Spatial attributes of Cerulean Warbler territories (use) and random non-use areas in Yellowwood and Morgan-Monroe
state forests in Southern Indiana. Results of 2-sample t-tests that were used to compare all attributes among areas are reported
below. Bonferroni adjustments were made for all multiple comparisons of variables that were not considered independent.
Attribute
Conclusion
Use (n)
Distance to stream
Distance to road
Distance to harvest
Distance to conifer patch
Slope
Aspect
Elevation
S
NS
NS
S
NS
S
NS
159
159
159
159
159
159
159
Non-use (n) Median (use) Median (non-use)
91
91
91
91
91
91
91
157.1
78
252
192.2
36.6
109.47
755.22
284.1
111.2
209
407.4
37.7
226.77
773.52
P
< 0.001
0.074
0.277
< 0.001
0.522
<0.001
0.21
Use (n) = number of territories. Non-use (n) = number of random non-use areas. Median (use) = median distance of territories
to attribute in m, with the exception of slope and aspect (degrees). Median (non-use) = median distance of random non-use
areas to attribute in m, with the exception of slope and aspect (degrees). S = significant. NS = not significant
-Chapter 2Conspecific Social Cues Strongly Influence Cerulean Warbler Male Settlement Patterns
in a Managed Forest
Ryan H. Dibala
43
Abstract
Population age-structure and differential settlement patterns may have
important consequences for reproductive output and population dynamics in bird
populations, especially those that are in sharp decline. The Cerulean Warbler
(Setophaga cerulea) is one species that has declined drastically throughout its range.
This species was monitored in Yellowwood and Morgan-Monroe state forests in
Southern Indiana to address questions pertaining to age-specific male settlement
patterns and clustered territoriality. A total of 130 male Cerulean Warblers were
detected and 101 territories were demarcated across eight of nine study sites. Thirty of
96 males (31%) were classified as second year (SY) birds, 66 of 96 (69%) were classified
as after second year (ASY) birds, and five birds remained of unknown age. Using a
nearest neighbor analysis, 80 of 101 (79.21%) territories located within five of eight
study sites were clustered. ASY males were no more likely to cluster than SY males (p =
0.258). SY male mean distance to ASY males was significantly closer than mean distance
to other SY males (p = 0.001). Similarly, ASY male mean distance to other ASY males was
significantly closer than mean distance to SY males (p = 0.001), showing that both ageclasses have a clear preference for settling closer to experienced males. There were no
differences in vegetation or distance to landscape features between the age-classes,
supporting social explanations for settlement. These results provide evidence that
Cerulean Warbler settlement patterns are strongly influenced by social cues.
Keywords: Cerulean Warbler, Setophaga cerulea, social attraction, age-structure, cluster
44
Introduction
Habitat selection of forest songbirds has been well studied (reviewed by Jones
2001 and Johnson 2007), perhaps most effectively by examining male settlement
patterns concomitantly with reproductive success in territorial species (Landmann and
Kollinsky 1995, Morris and Lemon 1988, Ficken and Ficken 1967, Holmes et al. 1996).
These studies have depicted the importance of accounting for both habitat components
and social mechanisms while evaluating habitat quality. Despite several informative
studies (Betts et al. 2008, Wagner 1997, Cornell and Donovan 2010, Muller et al. 1997),
the relative importance of habitat and social cues still remains largely unknown.
Instead of measuring territory quality directly in ways that would be difficult or
time-consuming, birds may need to rely on an indirect assessment of territory value,
such as using social cues from conspecifics (Stamps 1987). In fact, for many short-lived
species, relying on personally gathered information may be very costly (Stamps and
Krishnan 2005). Many studies have provided evidence that males may be attracted not
only to certain habitat characteristics but to various conspecific social cues (Collias and
Collias 1969, Wagner 1997, Muller et al. 1997). More recently, research has focused on
proximate cues provided by conspecifics (reviewed in Ahlering and Faaborg 2006) and a
growing body of evidence supports the hypothesis that social cues play an important
role in settlement (Muller et al. 1997, Danchin et al. 2000, Ward and Schlossberg 2004,
Betts et al. 2008, Cornell and Donovan 2010). For example, researchers have shown
45
that conspecific songs can have an effect on bird settlement patterns (Alatalo et al.
1982, Mills et al. 2006, Betts et al. 2008, Ward and Schlossberg 2004).
All-purpose territories are sometimes aggregated in dense concentrations, or
clusters, across the landscape leaving seemingly suitable habitats vacant (Stamps 1987).
This pattern has been observed in many species of New and Old World wood warblers,
including Black-throated Blue Warbler (Setophaga caerulescens, Holmes et al. 1996),
Wood Warbler (Phyloscopus sibilatrix, Herremans 1993), Yellow Warbler (Setophaga
petechial, Clark and Robertson 1979) and Kirtland’s Warbler (Setophaga kirtlandii,
Mayfield 1960, Burgoyne and Ryel 1978). At least eight hypotheses have been proposed
to explain clustering behavior in animals (see Tarof and Ratcliffe 2004), the most
common of which are the material resource hypothesis and the predation hypothesis
(Igor Dias et al. 2009). The former predicts clustered settlement to occur in response to
the patchiness of ecological resources such as vegetation or food (Kiester and Slatkin
1974). The presence of conspecifics could signal the availability of quality habitat at a
particular location (Stamps 1987, Danchin and Wagner 1997). The predation hypothesis
proposes that clustering reduces predation due to increased vigilance and
communication among conspecifics (Hamilton 1971).
A third explanation, known as the hidden-lek hypothesis, proposes that the
clustering of territories results from female pursuit of extra-pair copulations from high
quality males that are already socially paired (Wagner 1997). Additionally, large
aggregations could easily attract numerous females, making it easier for males to secure
46
a mate (Danchin and Wagner 1997). These explanations imply that because of their
naivety, young individuals should rely more heavily on conspecific cues than older, more
experienced individuals (Stamps 1987, Danchin et al. 2000). Thus, when studying male
settlement patterns it is essential to differentiate between naïve settlers from those
who are returning to previously used habitats (Muller et al. 1997).
In many species of birds, territory quality and associated breeding success
increases with age (Ficken and Ficken 1967, Hill 1988, Lozano et al. 1996). It has been
well documented that older males arrive on the breeding grounds earlier and are more
successful breeders than yearling males (Brown 1969, Fretwell and Lucas 1970, Hill
1988, Lozano et al. 1996, Muller et al. 1997). This late arrival could be an adaptive
response by young males to avoid intense competition early in the season (Hill 1988,
Morton and Derrickson 1990). Older birds have more familiarity with the breeding area
and by arriving earlier have the advantages of minimal competition for territory
placement, greater mate availability, and a longer overall breeding season. Conversely,
yearling males must establish territories wherever they can and therefore often occupy
lower quality habitat patches (Wooller and Coulson 1997, Newton 1988).
Examining differential settlement patterns and age-specific reproductive output
can provide important demographic information about breeding bird populations,
especially those that are in sharp decline. One species in particular, the Cerulean
Warbler (Setophaga cerulea), has become increasingly scarce across much of North
America. This long-distance Nearctic-Neotropical migrant has been described as a
47
“loosely colonial” species (Hamel 2000, Roth and Islam 2007) that engages in aggressive
territorial defense against conspecifics, providing an excellent study subject for
questions regarding intraspecific sociality and age-specific habitat differences. It is likely
that territory establishment and settlement patterns are influenced by both structural
habitat cues and social mechanisms. Cerulean Warblers are an area-sensitive species
that depend on large, contiguous blocks of mature deciduous forest and tall trees for
successful breeding (Lynch 1981, Hamel 2000, Jones and Robertson 2001, Roth and
Islam 2008). It appears that a heterogeneous, three-dimensional structure of the
canopy within the forest is an important landscape feature for this species (Lynch 1981,
Hamel 2000, Jones et al. 2001). In Ohio, Cerulean Warbler density and nesting success
were positively associated with canopy openness, numbers of large-diameter trees, and
number of grapevines (Bakermans and Rodewald 2009). However, if physical habitat
components were the only reason for clustering, then territories would be spaced more
evenly throughout the landscape (Roth and Islam 2007). Roth and Islam (2007)
observed that enough suitable and available habitats are left unoccupied by Cerulean
Warblers that social aspects must play an important role in settlement.
Yearling, or second year (SY) male fecundity and settlement patterns have not
been documented for the Cerulean Warbler and yet are critical in the evaluation of
breeding habitat and age-specific demography. Throughout the range of the Blackthroated Blue Warbler, Graves (1997) found a disproportionate number of yearling
males in geographically separated and peripheral habitats, possibly leading to the
48
formation of distinct “sink” populations. A study of breeding American Redstart
(Setophaga ruticilla) males showed that SY males were forced into marginal breeding
habitat by older males (Ficken and Ficken 1967, Sherry and Holmes 1989). In Southern
Ontario, Jones et al. (2004) thought 15% of Cerulean Warbler males were SY birds and in
Michigan, Rogers (2006) found Cerulean Warbler age structure to be strongly biased
toward older males and suggested that further research be conducted on habitat
specificity and reproductive success of age-structured breeding populations.
Investigating conspecific social dynamics along with site-specific vegetation structure
can help identify preferred Cerulean Warbler habitat.
The purpose of this study was to determine whether or not there were
differences in settlement patterns, territory size, reproductive success, and vegetation
structure between second year (SY) and after second year (ASY) males. The following
questions were addressed: 1) Where do SY and ASY males occur on the landscape? 2)
What is the age ratio of this particular population? 3.) What proportion of SY and ASY
males are clustered? 3) Is there a difference in territory sizes between age-classes? 4)
Are there differences in reproductive success between age-classes? 5) Are there
differences in physical habitat structure between age-classes? Based on a priori
published information indicating that experienced adults return to breeding sites
earliest and presumably have greater reproductive potential, I predicted that Cerulean
Warbler ASY males would account for the largest proportion of clustered territories and
reproductively successful individuals. I expected that ASY birds would defend larger
49
territories because of their greater level of experience and consequent resource-holding
potential. I also predicted that ASY birds would be associated with areas inhabited by
larger trees, grape vine, steeper slopes, and shrub cover, four variables that have been
shown to be important in Cerulean Warbler habitat selection (Hamel 2000, Bakermans
and Rodewald 2009, Kaminski 2010, Dibala unpublished data).
Materials and Methods
Focal Species and Study Area
The Cerulean Warbler is a Nearctic-Neotropical migrant songbird that breeds in
mature deciduous forests of eastern and central North America and winters on the
Andean slopes of northwestern South America (Hamel 2000). Due to loss of contiguous
forest cover and habitat fragmentation, this species is facing immediate threats in both
its breeding and wintering ranges. It is now considered North America’s fastest
declining wood warbler, as populations are estimated to have dropped by
approximately 70% since 1966 (Sauer et al. 2008). This decline is so alarming that the
species has been listed on the International Union for the Conservation of Nature’s
(IUCN) red list as “vulnerable” (Birdlife International 2004) and is considered stateendangered in Indiana. In fact, the threat is so high that a sense of urgency attends the
study of this species of concern (Hamel et al. 2004).
I studied Cerulean Warblers in 2010 and 2011 at nine management units
established by the Hardwood Ecosystem Experiment (HEE) in Brown, Morgan, and
50
Monroe counties of Southern Indiana. Launched in 2006, the HEE is a 100-year study
involving a consortium of state agencies and Universities to determine the effects of
forest management practices on native plants and animals of Indiana (HEE online). The
project encompasses nine management units (~282-363 ha) in Yellowwood and
Morgan- Monroe state forests in Southern Indiana (Figure 1, Chapter 1) and is
comprised of silviculture treatments grouped into one of two classifications: even-aged
and uneven-aged management (Thompson III et al. 1993). Harvests took place in the
summer of 2008, providing an excellent opportunity to monitor Cerulean Warbler
population response to human disturbance. The study site lies within the largest block
of contiguous forest in Southern Indiana and fits descriptions of quality Cerulean
Warbler habitat.
Point Count Surveys
One hundred-meter fixed radius point count surveys were conducted
throughout the month of May to locate singing males that were establishing territories.
Surveys were conducted within a 259 ha sample grid consisting of 49 bird survey points
(7x7; 1.96 km2 with a 50 m buffer). These points were arranged in seven north-south
transect lines with 200 m between each point to rule out the possibility of dual
detection (Jones et al. 2000, Hamel et al. 2009). Surveys were conducted between
05:30 and 10:30 EST and none took place on windy or rainy days. One point count was
conducted for each survey point and lasted five minutes. The first two minutes were
spent listening for singing males. This was followed by one minute of Cerulean Warbler
51
song broadcasting via an MP3 player and an external speaker to elicit a vocal response
from any males in the immediate area. The last two minutes were again spent listening
without playback (Falls 1981). When a bird was detected, its approximate distance from
the point and compass direction were recorded.
Territory Demarcation
Points where birds were initially heard were revisited to delineate territory
boundaries in 2010 and 2011. Male Cerulean Warblers were located by their incessant
singing, and trees in which birds sang repetitively were identified to species and marked
with flagging tape. A Garmin 76 handheld Global Positioning System (GPS) unit was
used to mark the location of the tree in a Universal Transverse Mercator (UTM)
coordinate system. A territory was considered complete only when between 5 and 12
trees had been recorded for an individual. Territory locations and sizes were analyzed
by creating minimum convex polygons in ArcMap (ArcGIS 10) and territory boundaries
were assessed based on their distance to landscape features and harvests.
Age-class Identification
Throughout the territory demarcation process, the resident male was viewed
with binoculars as many times as possible to begin assessing its age-class. Once a
minimum of five trees were marked for any particular territory, I navigated to the
approximate center of the territory and broadcasted a recording of a male song with an
MP3 player with an external speaker for one minute. The following two minutes were
52
spent listening and watching for the male and photographs were taken when possible.
If the bird did not approach within 15 m to make visual observations, another minute
was spent advertising the song. The last minute was spent listening and watching for
the resident male. To avoid creating a bias, playback song selection was kept consistent
across all territories. Additionally, playback was used conservatively so as not to overstimulate and increase aggressive interaction among neighboring birds. All behavioral
and physical observations were recorded for each territory.
Males were identified as either second year (SY) or after second year (ASY) by
documenting a combination of physical characteristics based off of field observation. SY
males were identified by the presence of a white superciliary stripe, incomplete or faint
breast band, and reduced streaking on the back. ASY males lack a prominent white
supercilium, possess a full, dark breast band, and are azure blue above with prominent
black streaking (Dunn and Garrett 1997). It is important to note that ASY males may
possess a small white remnant patch of the supercilium at the back of the eye.
Therefore, in order to confidently conclude that a male belonged to a particular ageclass, a combination of at least two of these three physical characteristics were
confirmed. All birds were observed from a distance of at least 15 m. Birds designated
to a particular age-class based on only one physical characteristic were excluded from
the data (See Appendix II). To eliminate potential observer bias, I made all final male
age-class identifications.
Reproductive Output
53
Nest searching commenced in late April of 2011. Direct observation of a female
on a male’s territory and her general behavior often exposed the location of the nest.
Audible cues were used readily in pinpointing the nest location, as a paired female
would often communicate to a nearby male with a high-pitched chip note and a mated
male would sing softly in close proximity to the nest (Barg et al. 2007). When a nest was
found, it was monitored closely at least once every two days and was determined
successful if at least one nestling fledged (Mayfield 1975). Additionally, all territories
where Cerulean Warbler fledglings were seen begging or being fed by adults were
considered successful. Because all territories were monitored closely throughout the
season and the twitter of fledglings was quite conspicuous, it is unlikely that fledglings
went undetected (Jones et al. 2004, Rogers 2006). Therefore, in addition to nests that
failed, I considered territories unsuccessful if no nest and/or fledglings were found.
Thus, I defined nesting success as: Successful nests + territories with
fledglings/unsuccessful nests + unknown.
Vegetation Sampling
Vegetation sampling began at the beginning of July when detection proved
difficult due to a substantial decrease in male singing rate. Sampling was conducted at
the center of each territory where a 0.04 ha circular plot was marked. Using the
methods of James and Shugart (1970), aspect was assessed at the plot’s origin and slope
was measured with a clinometer in each cardinal direction. Presence and absence of
canopy and ground cover were recorded with a GRS densitometer at 2 m intervals along
54
each cardinal direction of the plot. Woody plants with a diameter at breast height
(DBH) ≤3 cm and 3-10 cm were identified to species within a 5 m radius of the plot’s
center. In each quadrant, mature trees (>10 cm DBH) both living and dead were
identified to species and a rangefinder was used to measure the maximum canopy
height in each quadrant. The presence or absence of grapevine (Vitis sp.) within each
plot was also noted.
GIS Analysis
ArcMap (ArcGIS 10) was used to create a geodatabase in which all geospatial
data were displayed and analyzed. UTM coordinates were imported to ArcMap and
polygons were constructed using a two-step process: 1) triangular irregular networks
(TINs) were created to display three dimensional attributes in vector format and 2) an
attribute domain was then created to ensure data integrity. Each domain represented a
separate territory and included metadata about the shape’s length and area. Domains
were added to a larger feature class depending on individual datasets. For example,
separate feature classes were created for SY/ASY males as well as for clustered/nonclustered and reproductively successful/unsuccessful Cerulean Warblers. These layers
were superimposed onto GIS layers of the nine management units with associated
landscape features and harvest areas. These, along with raster data such as aerial
photographs and a digital elevation model (DEM) were obtained from the Indiana
Spatial Data Portal (Kaminski 2010). These files were used to analyze differences in
55
elevation, slope, and aspect of Cerulean Warbler territories that were derived from the
vector polygons using the zonal statistics tool under Zonal in Spatial Analyst Tools.
Territory centroids were created for polygon feature classes using the feature to
point tool. Distances were measured to and from the centroids of polygon features by
generating a Near Table under Proximity in Analysis Tools. Distances to landscape
features such as harvest areas, roads, streams, conifer stands, and neighboring
territories were calculated for SY and ASY males and clustered and non-clustered
territories. Additionally, territory sizes were compared between SY and ASY males and
clustered and non-clustered males.
Statistical Analyses
A Fisher’s Exact Test was used to determine differences in mating success
between males from the two age-classes. I used a two-sample t-test to determine
whether successful SY males could contribute their success to settling closer to any ASY
male, regardless of whether the ASY male was successful. Differences in vegetative
characteristics between the age-classes were investigated by using Multivariate Analysis
of Variance (MANOVA, Sharma 1996).
Clustering on the landscape was determined statistically by using the Average
Nearest Neighbor tool under Analyzing Patterns in Spatial Statistics tools. This tool
calculates the distances between the centroids of each territory and the nearest
neighboring territory and compares these values to the expected neighboring distances
56
if territories were dispersed randomly throughout the study area (Krebs 1989). The area
of each management unit (1.96 km2) was specified for each analysis and a z-test at α =
0.05 was used to determine if the spatial pattern of territories within each management
unit was clustered (Figure 1). Pooled data are presented for settlement patterns
observed in 2010 and 2011.
Two sample t-tests were used to test for differences (LeBlanc 2008) in spatial
attributes such as distances to landscape features (streams, roads, harvests), slope,
aspect, and elevation between age-classes. A paired t-test was used to compare the
distance of nearest neighboring SY and ASY males to members of each age class.
Additionally, nearest neighbor distance values that pooled both age-classes were
calculated for all territories and a Mann-Whitney U-test was used to test for differences
in settlement proximity. Bonferroni adjustments were made for multiple comparisons
of variables that were not considered independent.
All data were checked for normality and non-normal data were log-transformed.
In cases where the data were extremely positively skewed, the non-parametric MannWhitney U-test was used because of its higher power in these situations (LeBlanc
personal communication). Therefore, median values are presented in some cases. All
tests were performed with Minitab (Version 16) at α = 0.05.
Results
Age-class structure and Reproductive Success
57
A total of 130 male Cerulean Warblers were detected and 101 territories were
demarcated across eight of nine management units. Cerulean Warblers were absent in
the one unit when revisited and therefore no territories were marked in that unit.
Thirty of 101 males (29.70%) were classified as SY birds, 66 of 101 (65.35%) were
classified as ASY birds, and five birds (4.95%) remained of unknown age-class (Figure 2).
These five birds were excluded from all age-class comparison analyses. Thirty-one
territories (10 SY and 21 ASY) had either a successful nest or fledglings present. SY birds
made up nearly half of all successful males and no difference was found in reproductive
success between ASY and SY males (p = 1.000, Fisher’s Exact Test, Figure 3).
Additionally, reproductively successful SY males were no closer to ASY males than to
reproductively unsuccessful SY males (t = -1.37, p = 0.182, df = 27, 2-sample t-test with a
log transformation).
Vegetation
There were no differences in vegetative characteristics between SY and ASY male
Cerulean Warbler territories (Wilks’ λ, F11,37 = 0.794, p = 0.645).
Clustering
A total of 80 out of 101 (79.21%) territories located within five of eight
management units were clustered (Table 1). This is almost identical to clustering
patterns in 2010 where 46 of 58 (79.31%) territories and three of seven management
units were clustered. ASY males were no more likely to cluster than SY males (p = 0.258,
58
Fisher’s Exact Test). However, a Mann-Whitney U-test of nearest neighbor values
showed that ASY male median distance to nearest neighbor (74.8 m) was significantly
closer than SY male median distance to nearest neighbor (103 m, p = 0.030). There was
no significant difference in reproductive success between clustered and non-clustered
sites (p = 1.000, Fisher’s Exact Test). However, there was a significant difference in
median territory size between non-clustered territories (0.191 ha) and clustered
territories (0.143 ha, p = 0.0235, Mann-Whitney U-test). No differences existed
between clustered and non-clustered territories in median distances to streams (p =
0.843), roads (p = 0.642), and harvest areas (p = 0.256). Similarly, no differences were
found between the two groups in mean slope (p = 0.367), mean aspect (p = 0.891, with
a log transformation), and mean elevation (p = 0.240).
Settlement Patterns
Interestingly, SY male mean territory size was significantly larger than ASY mean
territory size (t = -2.09, p = 0.039, df = 94, 2-sample t-test with a log transformation,
Figure 4). SY male mean distance to ASY males (176.2 m) was significantly closer than
mean distance to other SY males (328.5 m, t = 3.58, p = 0.001, Figure 5). Similarly, ASY
male mean distance to other ASY males (123.3 m) was significantly closer than mean
distance to SY males (215 m, t = 3.33, p = 0.001, Figure 6), showing that both age-classes
have a clear preference for settling closer to experienced males. No differences were
found between age-classes in median distances to streams (p = 0.545), roads (p =
0.701), and harvest areas (p = 0.530). Likewise, there were no significant differences in
59
mean slope (p = 0.384) and elevation (p = 0.369), however median aspect differed
significantly between SY (90.46°) and ASY (116.53°) male territories (p = 0.013, MannWhitney U-test). SY males appear to be using easterly facing slopes while ASY males are
using southeasterly facing slopes (Table 2).
Discussion
Age-class Structure
I found that 29.70% of Cerulean Warbler males in Yellowwood and MorganMonroe state forests were SY birds. This is similar to the 27% SY proportion presented
by Boves (2011) in his four year study in the Appalachian Mountains. In Southern
Ontario, Jones et al. (2004) concluded that 15% of Cerulean Warbler males were SY
birds. At a study site in Michigan, Rogers (2006) claimed that SY birds made up 10-20%
of the male population. Multiple studies have suggested that there is wide variation in
SY birds among years. Holmes et al. (1992) found that numbers of ASY male Blackthroated Blue Warblers remained relatively stable whereas numbers of SY males
fluctuated widely over a four year period (31-56% of all males). In their study, the ratio
of SY/ASY males varied among years, with the highest percentage of SY males during
years of highest Black-throated Blue Warbler densities. Graves (1997) indicated that
Black-throated Blue Warbler yearling males exhibited substantial variation among years;
however, he found that peripheral habitats where relative abundance was lower had a
higher proportion of SY males. In a study conducted by Bayne and Hobson (2001), the
proportion of SY male Ovenbirds (Seiurus aurocapilla) was higher in farm fragments
60
than in forest fragments or contiguous forest. He suggested that a skewed age-ratio
among landscapes could mean that older males are forcing yearlings out of optimal
breeding habitats and into inferior areas.
Although there were no obvious examples of habitat segregation between the
age-classes on a local scale in Cerulean Warblers, larger landscape-level factors could be
playing a role in age-class structure. Yellowwood and Morgan-Monroe state forests are
large forested tracts of land that are located in the heart of the agricultural Midwest.
These forests could be acting as sink habitats for younger, less-experienced individuals
that are excluded from optimal breeding areas by adults (Cornell and Donovan 2010).
Buehler et al. (2008) reviewed Cerulean Warbler breeding studies throughout its range
and claimed that sites in non-forested landscapes such as Indiana may remain as sinks
without major landscape restoration. They conjectured that populations in these areas
are being maintained by immigration from other regions.
This hypothesis is not supported by the findings of Boves (2011), who
investigated the age structure of Cerulean Warblers in several areas throughout the
Appalachian Mountains and found that 27% of all males were SY birds. Considering that
this area is known to harbor the highest density of successfully breeding Cerulean
Warblers in North America (Buehler et al. 2008), the higher proportion of SY males
could suggest greater levels of annual recruitment, indicating the availability of higher
quality habitat. Future research is needed to investigate the age structure of Cerulean
61
Warbler populations within managed forests of the Midwest and other highly
fragmented landscapes and to determine how it compares to more contiguous forests.
Reproductive Output
There was no difference in reproductive success between the age-classes or nonclustered and clustered units. Jones et al. (2004) modeled SY fecundity as 80% that of
ASY males based on findings from other studies because no data existed for SY male
Cerulean Warbler reproductive success (Nolan 1978, Saether 1990, Forslund and Part
1995, Holmes et al. 1996). My research showed that nearly half (47.62%) of successful
Cerulean Warbler territories belonged to SY males. Since males of both age-classes
settled in similar areas, they likely had equal access to females. It may be likely that
mature adult males allow yearlings to settle in close proximity in order to increase their
opportunity for extra-pair copulations with the mates of yearling males (Barg et al.
2006, Boves 2011). Further study is needed to address age-specific fecundity in both
sexes, as the age of the female could play an even greater role in reproductive success
than the age of the male.
Vegetation
Both SY and ASY male Cerulean Warblers appear to be using similar habitats
based on vegetation structure. This supports the conclusions of Sherry and Holmes
(1989) who showed that there were no age-related habitat preferences among ageclasses in American Redstarts. Harrison and Green (2010) found no link between
62
vegetation characteristics and territory settlement patterns in the northern part of
Brewer’s Sparrow’s (Spizella breweri) breeding range. Instead, birds settled in areas
where the previous year’s reproductive success was high, indicating lower levels of
predation. Similarly, vegetation characteristics appeared to have little or no effect on
settlement patterns in Least Flycatchers Empidonax minimus (Tarof and Ratcliffe 2004),
Kirtland’s Warblers (Morse 1989), and Lazuli Buntings Passerina amoena (Green et al.
1996). However, several studies contradict these findings (Hill 1988, Holmes et al.
1996), showing that physical habitat characteristics differ between age-classes. It is
evident that the importance of habitat structure as it relates to age-specific settlement
may vary among species.
Settlement Patterns
My results confirm earlier findings that the Cerulean Warbler is a “loosely
colonial” species, likely using the presence of conspecifics as habitat-specific cues (Roth
and Islam 2007). I found that both ASY and SY males located their territories
significantly closer to ASY males than they did to other SY males. These findings suggest
that Cerulean Warblers are relying on the experience of older males when settling on
the landscape. Males may be attracted to conspecifics because of the greater likelihood
of females’ settling in places with higher densities of territorial males (Collias and Collias
1969, Wagner 1997, Stamps 1991). A dense concentration of females could cause latearriving SY males to settle near mature adults for access to mates. Another possibility is
that the presence of experienced individuals could be an indicator of high quality habitat
63
(Ward and Schlossberg 2004). In many species, individuals are more likely to return to a
particular site if they have reproduced successfully there the previous year (Bollinger &
Gavin 1989, Haas 1998). Therefore, settling closer to site-faithful males may be the best
way to seek out high quality habitat (Alatalo et al. 1982, Stamps 1991, Ward and
Schlossberg 2004).
A number of published studies provide similar evidence. Muller et al. (1997)
found that newly breeding House Wrens (Troglodytes aedon) select nest boxes that are
significantly closer to established adult male territories. A study on Black-throated Blue
Warblers found that males were four times more likely to settle in areas where playback
was used than in control areas (Betts et al. 2008). Additionally, they tested the
settlement response of both males and females to broadcasted vocalizations across a
gradient of vegetation types and found that neither shrub cover nor tree density
predicted warbler occurrence and that location cues trumped the use of vegetation
cues. Most interesting is their documentation of the apparent use of public information
to aide in settlement decisions the following spring. Beecher et al. (2007) proposed that
successful individuals sing more frequently later in the breeding season to influence
song development in offspring and thus provide valuable information to onlookers.
Similarly, habitats devoid of singing males late in the season may infer poor habitat
quality to prospecting conspecifics (Betts et al. 2008).
The smaller size of clustered territories was probably due to density-dependent
factors such as resource competition. A study of Dendroica warblers in spruce forests of
64
Maine found that species with dense populations had smaller territory sizes and vice
versa (Morse 1976). One of the many benefits of settling in a populated area is that
birds have to expend less energy when defending a smaller territory perimeter.
Territory sizes of SY males were significantly larger than those of ASY males.
Assuming ASY males occupy territories with greater food availability, this finding is
consistent with a study that analyzed the stomach contents of ovenbirds and showed
that territory size was inversely proportional to the amount of food available (Stenger
1958). Intuitively, the most dominant birds would occupy the highest quality habitat
and therefore, obtain equitable benefits from defending a smaller territory. However,
several studies have found either no difference in territory size or ASY territories to be
larger than SY territories (Benham et al. 2008, Ralph and Pearson 1971). More research
is needed to confirm if there are noticeable differences in territory size between the
age-classes in this species.
There were no differences in distance to important habitat features between the
age-classes and clustered and non-clustered areas. If ASY males settled significantly
closer to streams, a habitat feature shown to be important to this species (see Chapter
1), one could make a solid case for physical habitat differences between age-classes.
However, similar settlement proximity to habitat features negates this explanation and
further supports social explanations for settlement.
Conclusion and Management Implications
65
I have provided statistical evidence that both SY and ASY Cerulean Warbler males
are attracted to and settle closer to ASY males than other SY males. Social cues appear
to be playing an important role in settlement, a behavior that could have significant
conservation implications (Smith and Peacock 1990), and should be considered when
managing for this species. Kress (1997) first showed that seabird restoration on
uninhabited islands was possible when models, mirrors, and playbacks were used to
create the impression of a successful colony. Later, studies showed that social
attraction was possible for territorial species and that it was worth pursuing the use of
playback and models to influence settlement for theoretical and management reasons
(Mills et al. 2006, Alatalo et al. 1982, Muller et al. 1997). It is possible that vulnerable
songbirds like the Cerulean Warbler could be coaxed into settling on protected lands
where predators and brood parasites can be controlled and breeding success may be
higher. Ward and Schlossberg (2004) used playbacks to attract Black-capped Vireos
(Vireo atricapilla) to experimental plots where they were able to control Brown-headed
Cowbird (Molothrus ater) populations and thus increase the success rate relative to a
nearby unmanipulated population. Moreover, they showed that birds returned to
experimental plots the following year without the use of playback.
With that said, intraspecific sociality is rendered useless if adequate habitat is
limited or unavailable. Attention should be given to the characteristics of ASY male
territories, especially in areas that are re-occupied annually. Forests should be
manipulated in ways to promote those characteristics on the landscape. For example,
66
knowing that this population of ASY males most frequently settled on southeasterly
facing slopes, timber harvesting in these areas should be avoided where Cerulean
Warbler densities are high. Just as birds use public information to make informed
settlement decisions, researchers should observe bird behavior to help identify highly
productive areas. Likewise, logging should be avoided directly in those habitats.
The relatively high proportion of SY males and low overall fecundity of Cerulean
Warblers in Yellowwood and Morgan-Monroe state forests leads me to believe these
management areas are serving as habitat for a sink population. If yearlings are more
prevalent in modified and managed forests, the smaller number of more experienced
individuals may affect breeding productivity in such habitats (Holmes et al. 1992).
However, the importance of these forests should not be undermined. Less-preferred
areas provide refuge for less-competitive individuals and create buffer areas that can act
to mitigate population losses in source habitats (Bernstein et al. 1991).
A myriad of questions are yet to be asked regarding Cerulean Warbler age-class
structure and reproductive output. Future research should further investigate age-class
pairing success, where pairing occurs on the landscape and what Cerulean Warbler
density looks like where pairing is greatest. Also, frequency of site occupancy should be
monitored to determine whether ASY male territories are being used more frequently
than SY male territories. Additional reproductive and demographic data for Cerulean
Warblers in a variety of landscapes are needed to test the validity of the results
presented here. Continual monitoring of demographic dynamics in all areas of this
67
species’ range will be critical in deciding where and how to implement cost-effective
and feasible conservation strategies in the future. With this knowledge, appropriate
management decisions can be made to ensure that this denizen of the deciduous forest
has a place to return to year after year.
68
Literature Cited
Ahlering, M. A., and J. Faaborg. 2006. Avian habitat management meets conspecific
attraction: If you build it, will they come? Auk 123:301-312.
Alatalo, R. V., A. Lundberg, and M. Bjorklund. 1982. Can the song of male birds attract
other males? An experiment with the Pied Flycatcher Ficedula hypoleuca. Bird
Behaviour 4:42-45.
Bakermans, M. H. and A. D. Rodewald. 2009. Think globally, manage locally: The
importance of steady-state forest features for a declining songbird. Forest
Ecology and Management 258:224-232.
Barg, J. J., J. Jones, M. K. Girvan, and R. J. Robertson. 2006. Within-pair interactions and
parental behavior of Cerulean Warblers breeding in eastern Ontario. Wilson
Journal of Ornithology 118:316–325.
Barg, J. J., J. Jones and P. B. Hamel. 2007. Cerulean Warbler (Denroica cerulea) breeding
guide and nest searching tips (draft).
Bayne, E. M. and K. A. Hobson. 2001. Effects of habitat fragmentation on pairing
success of Ovenbirds: importance of male age and floater behavior. Auk
118:380-388.
Beecher, M. D., J. M. Burt, A. L. O’Loghlen, C. N. Templeton, and S. E. Campbell. 2007.
Bird song learning in an eavesdropping context. Animal Behavior 73:929-935.
Benham, P. M., M. T. Hallworth, and L. R. Reitsma. 2008. Does age influence territory
size, habitat selection, and reproductive success of male Canada Warblers in
Central New Hampshire? The Wilson Journal of Ornithology 120.3: 446+.
Bernstein, C., J. R. Krebs, and A. Kacelnik. 1991. Distribution of birds amongst habitats:
theory and relevance to conservation. Bird Population Studies: Relevance to
Conservation and Management (eds C. M. Perrins, J. –D. Lebreton and G. J. M.
Hirons), pp. 317-345. Oxford University Press, Oxford.
Betts, M. G., A. S. Hadley, N. Rodenhouse, and J. J. Nocera. 2008. Social information
trumps vegetation structure in breeding-site selection by a migrant songbird.
Proceedings of the Royal Society 275:2257-2263.
Birdlife International. 2004. Threatened Birds of the World. CD-ROM. Birdlife
International, Cambridge, UK.
69
Bollinger, E. K., and T. A. Gavin. 1989. The effects of site quality on breeding-site fidelity
in Bobolinks. Auk 106:584–594.
Boves, T. J. 2011. Multiple responses by Cerulean Warblers to experimental forest
disturbance in the Appalachian Mountains. PhD dissertation, University of
Tennessee, Knoxville, TN.
Brown, J. L. 1969. Territorial behavior and population regulation in birds: a review and
re-evaluation. Wilson Bulletin 81:293-329.
Buehler, D. A., J. J. Giocomo, J. Jones, P. B. Hamel, C. M. Rogers, T. A. Beachy, D. W.
Varble, C .P. Nicholson, K. L. Roth., J. Barg, R. J. Robertson, J. R. Robb, and K.
Islam. 2008. Cerulean Warbler Reproduction, Survival, and Models of
Population Decline. Journal of Wildlife Management 72:646-653.
Burgoyne, G. E., Jr., and L. A. Ryel. 1978. Kirtland’s Warbler numbers and colonies,
1977. Jack Pine Warbler 56:185-190.
Collias, N. E., and E. C. Collias. 1969. Size of breeding colonies related to attraction of
mates in a tropical passerine bird. Ecology 50:481-488.
Clark, K. L., and R. J. Robertson. 1979. Spatial and temporal multi-species nesting
aggregations in birds as anti-parasite and anti-predator defenses. Behavioral
Ecology and Sociobiology 5:359-371.
Cornell, K. L., and T. M. Donovan. 2010. Scale-dependent mechanisms of habitat
selection for a migratory passerine: an experimental approach. Auk 127:899
908.
Danchin, E., Boulinier, T., and F. Helfstein. 2000. Colonies as byproducts of commodity
selection. Behavioral Ecology 11:572-573.
Danchin, E., and R. H. Wagner. 1997. The evolution of coloniality: the emergence of
new perspectives. Trends in Ecology & Evolution 12:342-347.
Dunn, J. and K. Garrett. 1997. A field guide to warblers of North America. Boston, MA:
Houghton-Mifflin Co.
Falls, J. B. 1981. Mapping territories with playback: an accurate census method for
songbirds. Studies in Avian Biology 6:86-91.
Ficken, M. S., and R. W. Ficken. 1967. Age-specific differences in the breeding behavior
and ecology of the American Redstart. Wilson Bulletin 79:188-199.
70
Forslund, P., and T. Pärt. 1995. Age and reproduction in birds: Hypotheses and tests.
Trends in Ecology and Evolution 10:374-378.
Fretwell, S. D., and H. L. Lucas, Jr. 1970. On territorial behavior and other factors
influencing habitat distribution in birds. I. Theoretical development. Acta
Biotheoretica 19:16–36.
Graves, G. R. 1997. Geographic clines of age ratios of Black-throated Blue Warblers
(Dendroica caerulescens). Ecology 78:2524-2531.
Green, E., V. R. Muehter, and W. Davison. 1996. Lazuli Bunting (Passerina amoena). In
The Birds of North America, no. 232 (A. Poole and F Gill, Eds.). Academy of
Natural Sciences, Philadelphia, and American Ornithologists’ Union, Washington
D.C.
Haas, C. A. 1998. Effects of prior nesting success on site fidelity and breeding dispersal:
an experimental approach. Auk 115:929–936.
Hamel, P. B. 2000. Cerulean Warbler (Dendroica cerulea). The Birds of North America,
No. 511 (A. Poole and F. Gill, eds.). The Birds of North America, Inc.,
Philadelphia, PA.
Hamel, P. B., D. K. Dawson, and P. D. Keyser. 2004. How we can learn more about the
Cerulean Warbler (Dendroica cerulea). Auk 121:7-14.
Hamel, P. B., M. J. Welton, C. G. Smith, III, and R. P. Ford. 2009. Test of Partners in
Flight effective detection distance for cerulean warbler. Pp. 328–333 in Rich, T.
D., C. Arizmendi, D. W. Demarest, and C. Thompson (eds). Tundra to tropics:
connecting birds, habitats, and people. Proceedings of the 4th international
Partners in Flight conference 13-16 February 2008, McAllen, TX.
Hamilton, W. D. 1971. Geometry of the selfish herd. Journal of Theoretical Biology
31:295-311.
Hardwood Ecosystem Experiment. Online.
http://www.fnr.purdue.edu/HEE/Overview/Overview.htm
71
Harrison, M. L., and D. J. Green. 2010. Vegetation influences patch occupancy but not
settlement and dispersal decisions in a declining migratory songbird. Canadian
Journal of Zoology 88:148-160.
Herremens, M. 1993. Clustering of territories in the Wood Warbler Phylloscopus
sibilatrix. Bird Study 40:2-23.
Hill, G. E. 1988. Age, plumage brightness, territory quality, and reproductive success in
the Black-headed Grosbeak. Condor 2:379-388.
Holmes, R. T., T. W. Sherry, P. P. Marra, and K. E. Petit. 1992. Multiple brooding and
productivity of a Neotropical migrant, the Black-throated Blue Warbler
(Dendroica caerulescens) in an unfragmented temperate forest. Auk 109:321
333.
Holmes, R. T., P.P. Marra, and T. W. Sherry. 1996. Habitat-specific demography of
breeding Black-throated Blue Warblers (Dendroica caerulescens): Implications
for population dynamics. Journal of Animal Ecology 65:183-195.
Igor Dias, R., M. Kuhlmann, L. R. Lourenco, and R. H. Macedo. 2009. Territorial
clustering in the Blue- black Grassquit: Reproductive strategy in response to
habitat and food requirements? Condor 111:706-714.
James, F. C. and H. H. Shugart. 1970. A Quantitative Method of Habitat Description.
Audubon Field Notes 24:727-736.
Johnson, M. D. 2007. Measuring habitat quality: a review. Condor 109: 489-504.
Jones, J. 2001. Habitat selection studies in avian ecology: a critical review. Auk
118:557-562.
Jones, J. and R. J. Robertson. 2001. Territory and nest-site selection of Cerulean
Warblers in eastern Ontario. Auk 118:727-735.
Jones, J., R. D. DeBruyn, J. J. Barg, and R. J. Robertson. 2001. Assessing the effects of
natural disturbance on a Neotropical migrant songbird. Ecology 82:2628-2635.
Jones, J., W. J. McLeish, and R. J. Robertson. 2000. Density influences census technique
accuracy for Cerulean Warblers in eastern Ontario. Journal of Field Ornithology
71:46-56.
72
Jones, J., J. J. Barg, T. S. Sillett, M. L. Veit, and R. J. Robertson. 2004. Minimum
estimates of survival and population growth for Cerulean Warblers (Dendroica
cerulea) breeding in Ontario, Canada. Auk 121:15-24.
Kaminski, K. J. 2010. Cerulean Warbler Initial Response to Silviculture Treatments in
Southern Indiana. M.S. Thesis, Ball State University, Muncie, IN.
Kiester, A. R., and M. Slatkin. 1974. A strategy of movement and resource utilization.
Theoretical Population Biology 6:1-20.
Krebs, C.J. 1989. Ecological Methodology. University of British Columbia, Harper and
Row, New York, U.S.A.
Kress, S. W. 1997. Using animal behavior for conservation: case studies in seabird
restoration from the Maine coast, USA. Journal of the Yamashina Institute for
Ornithology 29:1–26.
Landmann, A., and C. Kollinsky. 1995. Age and plumage related territory differences in
male Black Redstarts - the (non)-adaptive significance of delayed plumage
maturation. Ethology Ecology and Evolution 7:147-167.
LeBlanc, D. 2008. Statistics: concepts and applications for science. XanEdu Publishers,
Michigan.
Lozano, G. A., S. Perreault, and R. E. Lemon. 1996. Age, arrival date and reproductive
success of male American Redstarts Setophaga ruticilla. Journal of Avian Biology
27:164-170.
Lynch, J.M., 1981. Status of the cerulean warbler in the Roanoke River basin of North
Carolina. Chat 45, 29-35.
Mayfield, H. 1960. The Kirtland’s Warbler. Cranbrook Institute of Science, Bloomfield
Hills, MI.
Mayfield, H. 1975. Suggestions for calculating nesting success. Wilson Bulletin 73:255
261.
Mills, A. M., J. D. Rising and D. A. Jackson. 2006. Conspecific attraction during
establishment of Least Flycatcher clusters. Journal of Field Ornithology 77:34-38.
Morris, M. M. J., and R. E. Lemon. 1988. Mate choice in American Redstarts: by
territory quality? Canadian Journal of Zoology 66:2255-2261.
73
Morse, D. H. 1976. Variables affecting the density and territory size of breeding spruce
woods warblers. Ecology 57:290-301.
Morse, D. H. 1989. American Warblers. Harvard University Press, Cambridge,
Massachusetts.
Morton, E. S. and K. C. Derrickson. 1990. The biological significance of age-specific
return schedules in breeding purple martins. Condor 92: 1040-1050.
Muller, K. L., J. A. Stamps, V. V. Krishnan, and N. H. Willits. 1997. The effects of
conspecific attraction and habitat quality on habitat selection in territorial birds
(Troglodytes aedon). American Naturalist 150:650-661.
Newton, I. 1988. Age and reproduction in the sparrowhawk. – In: Clutton-Brock, T.
(ed.) Reproductive Success. University of Chicago Press, Chicago, pp. 201-219.
Nolan, V., Jr. 1978. The ecology and behavior of the Prairie Warbler Dendroica discolor.
Ornithological Monographs, no. 26.
Ralph, C. J., and C. A. Pearson. 1971. Correlation of Age, Size of Territory, Plumage, and
Breeding Success in White-Crowned Sparrows. Condor 73:77-80.
Rogers, C. M. 2006. Nesting success and breeding biology of Cerulean Warblers in
Michigan. Wilson Journal of Ornithology 118:145-151.
Roth, K. L. and K. Islam. 2008. Habitat Selection and Reproductive Success of Cerulean
Warblers in Indiana. Wilson Journal of Ornithology 120:105-110.
Roth, K. L., and K. Islam. 2007. Do Cerulean Warblers (Dendroica cerulea) exhibit
clustered territoriality? American Midland-Naturalist 157:345-355.
Sæther, B.-E. 1990. Age-specific variation in reproductive performance of birds.
Current Ornithology 7:251-283.
Sauer, J. R., J. E. Hines and J. Fallon. [online]. 2008. The North American Breeding Bird
Survey,Results and Analysis 1966-2007 version 5.15,2008. USGS Patuxent
Wildlife Research Center, Laurel, Maryland, USA.
Sharma, S. 1996. Applied Multivariate Techniques. John Wile and Sons, Inc., New York.
Sherry, T. W., and R. T. Holmes. 1989. Age-specific social dominance affects habitat use
by breeding American Redstarts (Setophaga ruticilla): a removal experiment.
Behavioral Ecology and Sociobiology 25:327-333.
74
Smith, A. T., and M. M. Peacock. 1990. Conspecific attraction and the determination of
metapopulation colonization rates. Conservation Biology 4:320-323.
Stamps, J. A. 1987. Conspecifics as cues to territory quality: A preference of juvenile
lizards (Anolis aeneus) for previously used territories. American Naturalist
129:629-642.
Stamps, J. A. 1991. The effects of conspecifics on habitat selection in territorial species.
Behavioral Ecology and Sociobiology 28:29–36.
Stamps, J. A., and V. V. Krishnan. 2005. Nonintuitive cue use in habitat selection.
Ecology 86:2860-2867.
Stenger, J. 1958. Food habits and available food of Ovenbirds in relation to territory
size. Auk 75:335-346.
Tarof, S. A. and L. M. Ratcliffe. 2004. Habitat characteristics and nest predation do not
explain clustered breeding in Least Flycatchers (Empidonax minimus). Auk
121:877-893.
Thompson, F. R., J. R. Probst, and M. G. Raphael. 1993. Silvicultural options for
Neotropical migratory birds. In: D. M. Finch, P. W. Stangel, (eds.). Status and
management of neotropical migratory birds: September 21-25, 1992, Estes
Park, Colorado. General Technical Report RM 229. Fort Collins, CO.: Rocky
Mountain Forest and Range Experiment Station, U.S. Dept. of Agriculture, Forest
Service:353-362.
Wagner, R. H. 1997. Hidden leks: sexual selection and the clustering of avian territories.
Ornithological Monographs 49:123-146.
Ward, M., and S. Schlossberg. 2004. Conspecific attraction and the conservation of
territorial songbirds. Conservation Biology 18:519-525.
Wooller, R. D., and J. C. Coulson. 1977. Factors affecting the age of first breeding of the
kittiwake, Rissa tridactyla. Ibis 119:339-349.
75
ESRI 2011. ArcGIS Desktop: Release 10. Redlands, CA:
Environmental Systems Research Institute.
Figure 1. A sampling distribution of z-scores derived from the nearest neighbor tool in
ArcMap (ArcGIS 10) that is calculated by measuring the distances between the
centroids of each territory and comparing them to the expected values if the
centroids were randomly dispersed throughout the site (Krebs 1989).
76
Cerulean Warbler Male Age-class Structure in
Yellowwood and Morgan-Monroe State
Forests
4.95%
29.70%
65.35%
ASY
SY
UNK
Figure 2. Proportions of second year (SY), after second year (ASY), and unknown-age
male Cerulean Warblers recorded in the summer of 2011 in Morgan-Monroe and
Yellowwood state forests in Southern Indiana.
77
Figure 3. Differences in mating success between successful and unsuccessful second
year (SY) and successful and unsuccessful after second year (ASY) male Cerulean
Warblers in Yellowwood and Morgan-Monroe state forests, IN in the summer of 2011.
SY males make up nearly half of all successful territories.
78
Age-specific Territory Size
Log Territory Area (ha)
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
Log(SY)
Log(ASY)
Figure 4. Differences in territory size (log transformed) between second year (SY) and
after second year (ASY) male Cerulean Warblers in Yellowwood and Morgan-Monroe
state forests, IN in the summer of 2011. SY male territories are significantly larger than
ASY male territories.
79
SY Settlement To Both Age-Classes
Distance to nearest territory (m)
1000
800
600
400
200
0
SY-SY
SY-ASY
Figure 5. Second year (SY) male territory centroid distances to nearest territory centroid
of each age-class at Yellowwood and Morgan-Monroe state forests, IN in the summer of
2011. SY males settle significantly closer to ASY males than they do to other SY males.
80
ASY Settlement To Both Age-Classes
Distance to nearest territory (m)
1000
800
600
400
200
0
ASY-SY
ASY-ASY
Figure 6. After second year (ASY) male territory centroid distances to nearest territory
centroid of both age-classes at Yellowwood and Morgan-Monroe state forests, IN in the
summer of 2011. ASY males settle significantly closer to other ASY males than they do
to SY males.
81
Table 1. Nearest neighbor analysis values for Cerulean Warbler (Setophaga cerulea) territories in 2011 at Yellowwood and
Morgan-Monroe state forests in Southern Indiana. The area of each management unit (1.96 km2) was specified for all cluster
analyses.
Management Unit
Value
z
p
Status
n
Mean distance
SE
Unit 2
1.26
0.69
0.4902
Random
2
593.77
120.68
Unit 4
Unit 5
0.61
0.54
-2.35
-3.04
0.0186
0.0023
Clustered Clustered
10
12
129.29
104.4
82.28
88.74
Unit 3
0.86
-0.93
0.3514
Random
13
160.49
25.07
Unit 6
Unit 9
0.45
0.49
-3.91
-3.54
0.0001
0.0004
Clustered Clustered
14
13
81.18
90.41
97.63
95.15
Unit 1
NA
NA
NA
NA
0
NA
NA
Unit 7
0.88
-0.55
0.5828
Random
6
241.13
32.01
Unit 8
0.75
-2.67
0.0075
Clustered
31
90.02
30.15
82
Table 2. Spatial attributes of second year (SY) and after second year (ASY) male Cerulean Warbler territories in 2011 at
Yellowwood and Morgan-Monroe state forests in Southern Indiana. Results of 2-sample t-tests that were used to compare
all attributes among age-classes are reported below. Highlighted cells show p-values considered significant after Bonferroni
adjustments were made.
Attribute
Distance to stream
Distance to road
Distance to nearest neighbor
Distance to harvest
Slope
Aspect
Elevation
Conclusion
NS
NS
S
NS
NS
S
NS
SY (n)
30
30
30
30
30
30
30
ASY (n) SY (median) ASY (median)
66
135
155
66
81.94
78.93
66
103
74.8
66
341
277
66
34.39
36.51
66
90.46
116.5
66
742.4
757.9
P
0.545
0.701
0.03
0.53
0.384
0.013
0.369
SY (n) = number of second year birds. ASY (n) = number of after second year birds. Median SY = median distance of second
year male territories to attribute in m, with the exception of slope and aspect (degrees). Median ASY = median distance of
after second year male territories to attribute in m, with the exception of slope and aspect (degrees). NS = not significant. S
= significant.
83
Appendix I: UTM coordinates for Cerulean Warbler territories demarcated in the summers
of 2010 and 2011. East. = Easting and North. = Northing. * = Birds with less than 5 trees that
were not included in analyses.
2010
UNIT
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
NAME
PAN
PAN
PAN
PAN
PAN
DON*
DON*
DON*
DON*
KOZ
KOZ
KOZ
KOZ
KOZ
SUN*
SUN*
SUN*
SUN*
BUD
BUD
BUD
BUD
BUD
NIK*
NIK*
NIK*
NIK*
RED
RED
RED
RED
RED
RED
East.
548918
548910
548958
548913
548865
547936
547944
547885
547825
547093
547129
547091
547183
547154
547920
547856
547841
547843
548078
548039
548023
548047
548038
548301
548320
548341
548333
548369
548384
548361
548372
548390
548341
North.
4354674
4354671
4354622
4354585
4354692
4355241
4355185
4355194
4355187
4352109
4352046
4352057
4352021
4352073
4352159
4352141
4352187
4352165
4352062
4352055
4352071
4352059
4352071
4352065
4352075
4352096
4352097
4352112
4352103
4352158
4352165
4352162
4352099
2011
UNIT
2
2
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
NAME
JDAN
JDAN
JDAN
JDAN
JDAN
ERIC
ERIC
ERIC
ERIC
ERIC
ERIC
ERIC
CLAY
CLAY
CLAY
CLAY
CLAY
CLAY
ZORO
ZORO
ZORO
ZORO
ZORO
LUIS
LUIS
LUIS
LUIS
LUIS
LUIS
LUIS
LUIS
LUIS
LUIS
East.
548270
548294
548328
548302
548263
547826
547943
547906
547861
547809
547923
547782
548000
547993
547963
547989
548022
548025
547886
547842
547864
547871
547866
547200
547215
547163
547152
547211
547211
547181
547294
547282
547108
North.
4354888
4354896
4354856
4354867
4354903
4355359
4355251
4355245
4355252
4355261
4355219
4355331
4352179
4352170
4352162
4352152
4352162
4352129
4352532
4352517
4352529
4352541
4352591
4352017
4352029
4352061
4352051
4352045
4352007
4352046
4352104
4352073
4352088
84
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
BRO
BRO
BRO
BRO
BRO
TAZ
TAZ
TAZ
TAZ
TAZ
JAH
JAH
JAH
JAH
JAH
FRO
FRO
FRO
FRO
FRO
FRO
SAX
SAX
SAX
SAX
SAX
ACE
ACE
ACE
ACE
ACE
FLY
FLY
FLY
FLY
FLY
LUV
LUV
LUV
LUV
LUV
LUV
548373
548381
548412
548414
548396
548015
548022
548080
547998
547999
548433
548420
548396
548403
548423
548393
548380
548377
548357
548360
548356
548307
548314
548342
548331
548347
548279
548276
548304
548244
548257
547796
547820
547801
547759
547743
548392
548356
548345
548420
548405
548369
4352107
4352081
4352079
4352066
4352093
4352133
4352084
4352136
4352146
4352119
4351974
4351928
4351936
4351968
4351927
4351963
4351963
4351972
4351952
4351964
4351958
4352378
4352354
4352358
4352351
4352330
4352366
4352384
4352351
4352409
4352338
4352430
4352410
4352377
4352386
4352353
4352280
4352275
4352275
4352267
4352322
4352323
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
ROKO
ROKO
ROKO
ROKO
ROKO
PACO
PACO
PACO
PACO
PACO
PACO
ZEEK
ZEEK
ZEEK
ZEEK
ZEEK
ZEEK
ZEEK
NEPI
NEPI
NEPI
NEPI
NEPI
NEPI
BIRD
BIRD
BIRD
BIRD
BIRD
BIRD
LARY
LARY
LARY
LARY
LARY
LARY
NICK
NICK
NICK
NICK
NICK
NICK
547975
547985
548003
547999
547968
547903
547904
547940
547936
547913
547923
548372
548369
548367
548386
548402
548401
548405
548301
548300
548312
548340
548309
548335
547795
547797
547799
547776
547827
547801
547991
547983
547952
548001
548003
547980
548344
548342
548332
548338
548340
548344
4352401
4352386
4352389
4352420
4352378
4352279
4352294
4352323
4352314
4352270
4352375
4351964
4351988
4351993
4352001
4352011
4352006
4352038
4351979
4351986
4352002
4351991
4352019
4352002
4352535
4352512
4352523
4352556
4352454
4352490
4352725
4352735
4352750
4352734
4352773
4352675
4352082
4352091
4352094
4352051
4352058
4352052
85
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
5
5
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
KAM
KAM
KAM
KAM
KAM
PAT
PAT
PAT
PAT
PAT
KIM
KIM
KIM
KIM
KIM
GUS
GUS
GUS
GUS
GUS
GUS
ROY
ROY
ROY
ROY
ROY
ROY
MOE
MOE
MOE
MOE
MOE
JET
JET
JET
JET
JET
TAO
TAO
TAO
TAO
TAO
547711
547705
547752
547705
547738
548353
548321
548348
548302
548332
548359
548379
548367
548391
548387
554646
554593
554653
554660
554633
554612
553910
553889
553873
553891
553927
553895
555230
555229
555300
555206
555209
554923
554906
554857
554867
554880
554671
554688
554613
554634
554710
4352392
4352404
4352458
4352397
4352393
4352228
4352257
4352268
4352256
4352302
4352227
4352218
4352208
4352278
4352211
4339292
4339393
4339282
4339330
4339382
4339342
4339950
4339935
4340022
4340071
4340018
4340020
4330420
4330407
4330393
4330406
4330412
4330632
4330626
4330619
4330594
4330636
4330771
4330782
4330811
4330797
4330774
3
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
NICK
AMOS
AMOS
AMOS
AMOS
AMOS
FRIZ
FRIZ
FRIZ
FRIZ
FRIZ
JEFF
JEFF
JEFF
JEFF
JEFF
JEFF
BART
BART
BART
BART
BART
BART
BART
ZEUS
ZEUS
ZEUS
ZEUS
ZEUS
ZEUS
THOR
THOR
THOR
THOR
THOR
THOR
THOR
ARUN
ARUN
ARUN
ARUN
ARUN
548320
547969
547994
547957
547950
547969
548093
548070
548058
548088
548086
549136
549151
549151
549156
549154
549141
549153
549136
549164
549155
549121
549133
549118
550270
550238
550236
550223
550235
550228
550144
550095
550088
550127
550111
550158
550082
549047
549091
549160
549162
549126
4352063
4351765
4351723
4351698
4351673
4351678
4352046
4352071
4352079
4352098
4352067
4350665
4350655
4350691
4350625
4350664
4350677
4350703
4350722
4350725
4350732
4350724
4350726
4350719
4351215
4351271
4351219
4351256
4351205
4351212
4351201
4351271
4351282
4351346
4351337
4351309
4351221
4350909
4350933
4350876
4350809
4350845
86
6
6
6
6
6
6
6
6
6
6
6
6
6
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
8
8
8
8
8
8
8
8
8
8
TAO
TAO
SAM
SAM
SAM
SAM
SAM
BLU
BLU
BLU
BLU
BLU
BLU
BAM
BAM
BAM
BAM
BAM
BAM
ZIP
ZIP
ZIP
ZIP
ZIP
SKY
SKY
SKY
SKY
SKY
SKY
SKY
SKY
BOB
BOB
BOB
BOB
BOB
BOB
TIM
TIM
TIM
TIM
554707
554696
555223
555157
555158
555203
555204
555026
555057
554991
555020
555048
555095
558618
558626
558639
558620
558601
558601
558268
558258
558235
558223
558232
558559
558559
558583
558576
558586
558564
558528
558542
558293
558285
558276
558255
558227
558278
558399
558403
558375
558391
4330741
4330734
4330780
4330800
4330816
4330786
4330835
4330609
4330673
4330702
4330716
4330749
4330753
4331826
4331842
4331882
4331863
4331846
4331835
4331321
4331346
4331328
4331336
4331265
4331648
4331673
4331679
4331673
4331648
4331641
4331643
4331662
4329264
4329241
4329228
4329212
4329227
4329213
4329349
4329324
4329262
4329257
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
5
5
5
5
ARUN
MARS
MARS
MARS
MARS
MARS
HALF
HALF
HALF
HALF
HALF
NEWB
NEWB
NEWB
NEWB
NEWB
NEWB
NEWB
STAN
STAN
STAN
STAN
STAN
HANK
HANK
HANK
HANK
HANK
HUGH
HUGH
HUGH
HUGH
HUGH
JAZZ
JAZZ
JAZZ
JAZZ
JAZZ
JAZZ
NORM
NORM
NORM
549130
550241
550226
550222
550201
550243
550355
550344
550347
550390
550343
550136
550068
550079
550022
550028
550084
550162
550218
550288
550356
550336
550266
550280
550204
550242
550281
550269
553992
553986
553992
553983
553983
554008
554015
554052
554054
554060
554100
554175
554156
554148
4350834
4351171
4351120
4351158
4351165
4351158
4351224
4351175
4351189
4351260
4351267
4350724
4350705
4350701
4350724
4350710
4350761
4350704
4350423
4350458
4350528
4350592
4350479
4350343
4350370
4350383
4350370
4350354
4338971
4338963
4338958
4338962
4338973
4339007
4339026
4339006
4339016
4339027
4339024
4339999
4340036
4340016
87
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
TIM
TIM
TIM
TED
TED
TED
TED
TED
TED
WES
WES
WES
WES
WES
JOE
JOE
JOE
JOE
JOE
JOE
BIL
BIL
BIL
BIL
BIL
SLY
SLY
SLY
SLY
SLY
BEN
BEN
BEN
BEN
BEN
JIM
JIM
JIM
JIM
JIM
JIM
ABE
558359
558370
558390
559195
559197
559192
559122
559147
559170
558932
558942
558952
558959
558973
559145
559155
559164
559251
559240
559251
559149
559145
559162
559111
559160
558358
558344
558346
558346
558349
558312
558346
558322
558289
558292
558924
558968
558968
558984
558981
558974
558560
4329257
4329308
4329310
4329648
4329642
4329633
4329659
4329702
4329677
4329637
4329629
4329625
4329604
4392614
4329661
4329671
4329648
4329603
4329544
4329577
4329660
4329681
4329691
4329735
4329752
4329356
4329354
4329348
4329364
4329368
4329259
4329297
4329305
4329281
4329255
4329669
4329666
4329642
4329640
4329626
4329617
4329457
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
NORM
NORM
MORT
MORT
MORT
MORT
MORT
TIKI
TIKI
TIKI
TIKI
TIKI
SMIT
SMIT
SMIT
SMIT
SMIT
SMIT
SMIT
YORK
YORK
YORK
YORK
YORK
YORK
HAWK
HAWK
HAWK
HAWK
HAWK
HAWK
HAWK
THUG
THUG
THUG
THUG
THUG
BONO
BONO
BONO
BONO
BONO
554166
554180
554167
554175
554180
554181
554199
554665
554665
554683
554643
554634
554716
554712
554691
554685
554704
554735
554742
554823
554838
554818
554821
554817
554829
554836
554830
554815
554867
554863
554906
554775
555070
555138
555053
555074
555099
554717
554715
554751
554754
554745
4339967
4339953
4340072
4340072
4340063
4340060
4340071
4339416
4339429
4339388
4339398
4339408
4339282
4339279
4339253
4339273
4339325
4339323
4339310
4339677
4339686
4339680
4339674
4339699
4339679
4339729
4339736
4339730
4339706
4339733
4339731
4339713
4339403
4339251
4339268
4339307
4339269
4339227
4339188
4339158
4339189
4339186
88
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
ABE
ABE
ABE
ABE
MRT
MRT
MRT
MRT
MRT
MRT
MRT
MRT
MRT
MRT
VOZ
VOZ
VOZ
VOZ
VOZ
VOZ
VOZ
VOZ
PAC
PAC
PAC
PAC
PAC
MAN
MAN
MAN
MAN
MAN
BUB
BUB
BUB
BUB
BUB
STU
STU
STU
STU
STU
558575
558600
558565
558576
558721
558759
558744
558741
558754
558750
558853
558861
558851
558848
558311
558316
558319
558271
558261
558300
558309
558378
558105
558094
558104
558103
558108
558081
558078
558066
558075
558061
558124
558149
558142
558147
558144
558147
558153
558173
558171
558152
4329438
4329435
4329422
4329431
4329440
4329381
4329373
4329362
4329364
4329431
4329320
4329327
4329338
4329220
4329531
4329472
4329442
4329450
4329463
4329451
4329376
4329438
4329558
4329550
4329362
4329536
4329559
4329509
4329524
4329523
4329536
4329544
4329553
4329553
4329564
4329557
4329569
4329504
4329512
4329495
4329482
4329522
5
5
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
LARS
LARS
LARS
LARS
LARS
NERO
NERO
NERO
NERO
NERO
NERO
NERO
DOUG
DOUG
DOUG
DOUG
DOUG
DOUG
SHAQ
SHAQ
SHAQ
SHAQ
SHAQ
SHAQ
SHAQ
SHAQ
TOVE
TOVE
TOVE
TOVE
TOVE
TOVE
GRIZ
GRIZ
GRIZ
GRIZ
GRIZ
BEAR
BEAR
BEAR
BEAR
BEAR
554173
554139
554153
554121
554138
554671
554659
554675
554681
554693
554644
554668
554581
554569
554590
554595
554568
554585
554744
554740
554709
554719
554735
554784
554815
554714
554551
554545
554546
554558
554545
554532
554839
554861
554851
554855
554791
554332
554323
554323
554340
554335
4338829
4338810
4338793
4338866
4338869
4339319
4339293
4339331
4339287
4339320
4339317
4339362
4330679
4330659
4330655
4330656
4330663
4330659
4330461
4330492
4330494
4330483
4330366
4330342
4330360
4330492
4330670
4330660
4330651
4330641
4330641
4330639
4330619
4330653
4330657
4330667
4330622
4330821
4330799
4330806
4330788
4330781
89
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
TOM*
TOM*
TOM*
TOM*
NED
NED
NED
NED
NED
PAW
PAW
PAW
PAW
PAW
DAN
DAN
DAN
DAN
DAN
RON
RON
RON
RON
RON
TEK
TEK
TEK
TEK
TEK
BAL*
BAL*
BAL*
JIB
JIB
JIB
JIB
JIB
MAX*
MAX*
MAX*
MAX*
JER
560684
560678
560635
560627
560606
560578
560558
560564
560622
560831
560847
560867
560850
560830
560787
560780
560805
560828
560840
560879
560850
560862
560840
560835
560725
560743
560766
560778
560750
560926
560919
560926
560814
560809
560791
560771
560784
560594
560588
560588
560625
560597
4332583
4332609
4332610
4332616
4332312
4332272
4332293
4332367
4332346
4332401
4332411
4332385
4332402
4332381
4332622
4332637
4332568
4332570
4332580
4332733
4332779
4332747
4332745
4332700
4332510
4332522
4332543
4332533
4332563
4332459
4332449
4332468
4332691
4332703
4332712
4332692
4332704
4332912
4332899
4332859
4332922
4332743
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
BEAR
RICK
RICK
RICK
RICK
RICK
RICK
KING
KING
KING
KING
KING
FATS
FATS
FATS
FATS
FATS
FATS
WADE
WADE
WADE
WADE
WADE
WADE
WADE
FRED
FRED
FRED
FRED
FRED
BRET
BRET
BRET
BRET
BRET
BRET
MOON
MOON
MOON
MOON
MOON
SEAN
554351
554911
554891
554919
554995
554891
554932
555039
555040
555094
555103
555060
554542
554516
554512
554485
554485
554509
554653
554661
554664
554653
554662
554656
554665
554509
554508
554497
554499
5554500
554584
554562
554560
554567
554568
554575
554509
554509
554512
554520
554531
554613
4330790
4330598
4330601
4330648
4330624
4330613
4330638
4330614
4330596
4330627
4330657
4330577
4330893
4330775
4330824
4330819
4330784
4330759
4330495
4330499
4330480
4330459
4330447
4330470
4330489
4330651
4330652
4330650
4330640
4330645
4330575
4330573
4330556
4330540
4330544
4330580
4330601
4330664
4330670
4330650
4330674
4330595
90
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
JER
JER
JER
JER
JER
JER
ASH*
ASH*
ASH*
PIP
PIP
PIP
PIP
PIP
PIP
PIP
PIP
YEN
YEN
YEN
YEN
YEN
DRU*
DRU*
DRU*
DRU*
560611
560557
560577
560606
560512
560582
560532
560579
560544
560742
560758
560720
560713
560741
560749
560758
560774
560696
560698
560751
560684
560675
560746
560735
560732
560739
4332718
4332744
4332826
4332786
4332727
4332776
4332888
4332905
4332916
4332557
4332525
4332560
4332562
4332589
4332587
4332597
4332586
4332829
4332872
4332851
4332834
4332830
4332616
4332621
4332640
4332635
6
6
6
6
6
6
6
6
6
6
6
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
SEAN
SEAN
SEAN
SEAN
SEAN
MARK
MARK
MARK
MARK
MARK
MARK
ZIGI
ZIGI
ZIGI
ZIGI
ZIGI
ZIGI
OZZY
OZZY
OZZY
OZZY
OZZY
ZAGI
ZAGI
ZAGI
ZAGI
ZAGI
ALEX
ALEX
ALEX
ALEX
ALEX
ALEX
ALEX
LEON
LEON
LEON
LEON
LEON
LEON
LEON
LEON
554605
554592
554575
554556
554581
554615
554625
554635
554630
554641
554615
558763
558747
558731
558708
558741
558760
558807
558792
558798
558776
558821
558787
558795
558804
558836
558842
558727
558705
558694
558748
558738
558700
558713
558593
558608
558642
558566
558630
558607
558623
558608
4330588
4330586
4330601
4330669
4330616
4330542
4330555
4330586
4330570
4330537
4330515
4331243
4331317
4331279
4331322
4331326
4331380
4331424
4331350
4331349
4331422
4331470
4331231
4331271
4331232
4331173
4331171
4331675
4331688
4331639
4331671
4331665
4331660
4331700
4332008
4331983
4332058
4332004
4331938
4331960
4331872
4331888
91
7
7
7
7
7
7
7
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
LEON
ZITO
ZITO
ZITO
ZITO
ZITO
ZITO
HANS
HANS
HANS
HANS
HANS
CHAD
CHAD
CHAD
CHAD
CHAD
KURT
KURT
KURT
KURT
KURT
SLIM
SLIM
SLIM
SLIM
SLIM
HICK
HICK
HICK
HICK
HICK
RIFF
RIFF
RIFF
RIFF
RIFF
RIFF
RIFF
RIFF
RIFF
JAKE
558617
558197
558200
558243
558261
558218
558205
558940
558947
558943
558946
558953
558790
558794
558801
558815
558806
558871
558900
558876
558860
558843
558633
558623
558643
558644
558632
558605
558592
558579
558565
558574
558643
558664
558698
558682
558650
558657
558633
558628
558632
558584
4331798
4331193
4331202
4331266
4331307
4331187
4331080
4329517
4329510
4329530
4329496
4329527
4329427
4329424
4329417
4329442
4329439
4329554
4329564
4329548
4329565
4329547
4329127
4329084
4329089
4329081
4329079
4329096
4329057
4329087
4329092
4329084
4329139
4329208
4329178
4329141
4329087
4329080
4329090
4329101
4329111
4329357
92
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
JAKE
JAKE
JAKE
JAKE
FRAN
FRAN
FRAN
FRAN
FRAN
FRAN
FRAN
FRAN
FRAN
FRAN
FRAN
FRAN
GREG
GREG
GREG
GREG
GREG
MIKE
MIKE
MIKE
MIKE
MIKE
MIKE
MIKE
MIKE
CHAN
CHAN
CHAN
CHAN
CHAN
CHAN
CHAN
CHAN
REXX
REXX
REXX
REXX
REXX
558607
558615
558534
558551
559055
559054
559037
559057
559055
559054
559037
559057
559081
559082
559085
559046
559077
559062
559074
559074
559097
558133
558111
558133
558088
558107
558116
558120
558118
558131
558123
558110
558114
558090
558096
558064
558160
558166
558155
558176
558139
558169
4329314
4329355
4329320
4329331
4329635
4329640
4329654
4329649
4329635
4329640
4329654
4329649
4329655
4329633
4329620
4329605
4329639
4329653
4329673
4329662
4329727
4329277
4329245
4329250
4329250
4329262
4329226
4329183
4329280
4329139
4329147
4329148
4329135
4329138
4329162
4329105
4329114
4329186
4329161
4329189
4329220
4329195
93
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
REXX
JACK
JACK
JACK
JACK
JACK
JACK
JUAN
JUAN
JUAN
JUAN
JUAN
JUAN
ERNY
ERNY
ERNY
ERNY
ERNY
BERT
BERT
BERT
BERT
BERT
TINY
TINY
TINY
TINY
TINY
TINY
TINY
ANDY
ANDY
ANDY
ANDY
ANDY
BABE
BABE
BABE
BABE
BABE
BABE
BABE
558121
558070
558061
558049
558066
558000
557997
558274
558323
558321
558320
558296
558302
558525
558563
558570
558563
558566
558466
558487
558528
558529
558470
558520
558550
558558
558537
558578
558594
558518
558543
558567
558565
558512
558591
557859
557838
557893
557860
557851
557868
557908
4329203
4329075
4329051
4329035
4329030
4329057
4329050
4329228
4329199
4329177
4329284
4329252
4329248
4329520
4329521
4329527
4329542
4329555
4329950
4330064
4330025
4330057
4329991
4329994
4329964
4330007
4329976
4329935
4329943
4329985
4329091
4329099
4329092
4329116
4329082
4329150
4329164
4329163
4329109
4329148
4329151
4329140
94
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
RALF
RALF
RALF
RALF
RALF
RALF
RALF
RALF
RALF
STUD
STUD
STUD
STUD
STUD
DAVE
DAVE
DAVE
DAVE
DAVE
ZACK
ZACK
ZACK
ZACK
ZACK
ZACK
MELO
MELO
MELO
MELO
MELO
MELO
MELO
TATE
TATE
TATE
TATE
TATE
TATE
TATE
ALFE
ALFE
ALFE
557914
557914
557884
57892
557922
557927
557925
557880
557831
559072
559067
559036
559030
559023
558881
558831
558859
558830
558804
559092
559095
559104
559124
559082
559046
558935
558941
558950
558946
558925
558920
558936
558742
558747
558753
558729
558731
558622
558617
557841
557888
557923
4329053
4329047
4329089
4329087
4329175
4329053
4329046
4329123
4329094
4329932
4329931
4329941
4329936
4329995
4329651
4329578
4329657
4329604
4329610
4329810
4329805
4329783
4329788
4329832
4329854
4329665
4329658
4329669
4329662
4329700
4329676
4329638
4329418
4329415
4329407
4329414
4329389
4329454
4329458
4329346
4329302
4329343
95
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
9
9
9
9
9
9
9
9
ALFE
ALFE
CHIP
CHIP
CHIP
CHIP
CHIP
MARV
MARV
MARV
MARV
MARV
MARV
MARV
DUKE
DUKE
DUKE
DUKE
DUKE
DUKE
YUNG
YUNG
YUNG
YUNG
YUNG
JOSH
JOSH
JOSH
JOSH
JOSH
JOSH
JOSH
JOSH
JOSH
BILL
BILL
BILL
BILL
BILL
BILL
CAIN
CAIN
557855
557865
557979
557950
557969
557927
557945
558413
558433
558437
558393
558455
558487
558472
557999
558022
558040
557996
557978
558023
558341
558366
558362
558369
558373
558833
558834
558795
558859
558858
558869
558874
558879
558915
560536
560526
560544
560546
560513
560500
560701
560692
4329356
4329292
4329133
4329162
4329147
4329149
4329161
4329371
4329394
4329424
4329387
4329379
4329360
4329321
4329075
4329013
4329012
4328995
4328973
4328980
4329353
4329365
4329379
4329410
4329438
4330083
4330065
4330052
4330106
4330086
4330098
4330143
4330163
4330124
4332781
4332779
4332799
4332805
4332820
4332818
432516
4332499
96
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
CAIN
CAIN
CAIN
CAIN
WALT
WALT
WALT
WALT
WALT
MATT
MATT
MATT
MATT
MATT
LUKE
LUKE
LUKE
LUKE
LUKE
LUKE
PETE
PETE
PETE
PETE
PETE
PETE
PAUL
PAUL
PAUL
PAUL
PAUL
PAUL
PAUL
PAUL
KENT
KENT
KENT
KENT
KENT
KENT
ABEL
ABEL
560715
560677
560715
560697
560543
560551
560550
560530
560573
560777
560771
560785
560762
560801
560718
560708
560694
560720
560724
560712
561000
560994
560977
560950
560894
560873
560804
560749
560736
560735
560731
560725
560729
560766
560853
560791
560794
560804
560812
560835
560675
560707
4332516
4332507
4332519
4332531
4332632
4332638
4332620
4332648
4332654
4332709
4332701
4332721
4332746
4332774
4332613
4332607
4332611
4332644
4332659
4332636
4332172
4332186
4332144
4332198
4332122
4332148
4332672
4332679
4332694
4332674
4332672
4332671
4332675
4332699
4332683
4332683
4332687
4332670
4332681
4332666
4332484
4332493
97
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
ABEL
ABEL
ABEL
ABEL
ABEL
JOHN
JOHN
JOHN
JOHN
JOHN
RYAN
RYAN
RYAN
RYAN
RYAN
RYAN
RYAN
ADAM
ADAM
ADAM
ADAM
ADAM
ADAM
ADAM
ADAM
JOSE
JOSE
JOSE
JOSE
JOSE
JOSE
JOSE
JOSE
JOSE
JOSE
JOSE
JOSE
JOSE
JOSE
JOSE
JOSE
JOSE
560711
560712
560721
560737
560779
560792
560817
560845
560812
560788
560560
560576
560577
560602
560604
560614
560581
560725
560728
560730
560745
560719
560713
560740
560721
560650
560648
560663
560670
560657
560634
560654
560699
560709
560723
560735
560762
560637
560648
560663
560676
560693
4332498
4332518
4332521
4332538
4332466
4332571
4332594
4332599
4332651
4332637
4332782
4332781
4332787
4332791
4332808
4332740
4332785
4332521
4332540
4332541
4332552
4332555
4332541
4332566
4332570
4332473
4332452
4332466
4332484
4332464
4332482
4332470
4332380
4332373
4332374
4332365
4332436
4332398
4332402
4332420
4332452
4332452
98
Appendix II
Protocol for Observing and Recording Male Age-class
Objective: To determine if there is a significant difference between the numbers of
successfully nesting adult males and first spring males.
Ho: Adult males have no reproductive advantage over first spring males.
Ha: Adult males have a significant reproductive advantage over first spring males.
Methods: Throughout the territory demarcation process, the resident male should be
viewed in binoculars as many times as possible to begin assessing its age-class. Once a
minimum of five trees have been marked for any particular territory, researchers will
navigate to the approximate middle of the territory and a playback recording of a male
song will be played for one minute. The next two minutes will be spent listening and
watching for the male, where photographs will be taken of the individual, if at all
possible. If the bird does not approach within an adequate distance to make visual
observations, another minute will be spent playing the song recording. The last minute
will again be spent listening and watching for the male. To avoid creating a bias, ensure
that playback song selection is consistent across all territories. Also, use caution not to
overuse the playback, as it can increase aggressive interaction among neighboring birds
99
and complicate the age-class identification process. All behavioral and physical
observations should be recorded, along with song rate in the territory data sheet.
Males will be identified as either second year (SY) or after second year (ASY) by
documenting a combination of physical characteristics. SY males will be identified by
the presence of a white superciliary stripe, incomplete or faint breast band, and reduced
streaking on the back. ASY males lack a prominent white supercilium, possess a full,
dark breast band, and are azure blue above with prominent streaking (Dunn and Garrett
1997). It is important to note that mature adults may possess a small white remnant
patch of the supercilium at the back of the eye. Therefore, in order to confidently claim
that a male belongs to a particular age-class, a combination of at least two of these
three physical characteristics must be confirmed. Birds allocated to a particular ageclass based on only one physical characteristic will be excluded from the data. To
eliminate potential observer bias, all final decisions regarding male age-class must be
made by the principal investigator.
Below are pictures of first spring and mature adult males. Often times, physical
characteristics can be nebulous or enter a “gray zone.” Investigators should use the
images below as an aid in age-class identification in the field.
100
SY males are on the left and ASY males are on the right
101
102
103
APPENDIX III
TERRITORY SIZES (HA) FOR ALL YEARS
2007
0.445265
0.020797
0.187022
0.039364
0.061989
0.21123
0.027715
0.204284
0.191496
0.103618
0.014701
0.132308
0.149518
0.287423
0.304575
0.058176
0.215181
0.177808
0.102048
0.019304
0.131958
0.264194
1.1827
0.04036
0.168313
0.176491
0.185058
0.035873
0.131264
0.508268
0.113206
0.037915
0.36023
0.045918
2008
0.835524
0.118704
0.190432
0.081238
0.35086
0.197855
0.165846
0.790938
0.820591
1.751274
1.668189
0.613087
0.044386
0.082035
0.339199
0.188786
0.213
0.206114
0.161497
0.126469
0.311869
0.303584
0.260849
0.239235
0.264297
0.038891
0.19712
0.32699
0.019045
0.369683
0.136684
0.129905
0.121125
0.433945
2009
0.064153
0.14154
0.197289
0.085385
0.351376
0.746663
0.432932
0.119464
0.053862
0.117407
0.069389
0.120301
0.381034
0.302855
0.044478
0.235291
0.054505
0.434414
0.067244
0.166851
0.584743
0.262545
0.811675
0.096735
0.145744
0.221811
0.261958
0.027356
0.118867
0.687774
0.057566
0.435347
0.150944
0.027549
2010
0.0645
0.1931
0.0556
0.00315
0.08355
0.1497
0.2588
0.6743
0.1592
0.06435
0.02
0.04355
0.14605
0.3324
0.0146
0.24415
0.0355
0.32005
0.11385
0.6079
0.13015
0.05255
0.14185
0.4409
0.13355
0.1172
0.3492
0.28785
0.0292
0.09115
0.0865
1.20765
0.3567
0.02385
2011
0.0921
0.0471
0.00675
0.05075
0.0744
0.0973
0.2676
0.2091
0.3223
0.7826
0.03325
0.1475
0.1465
0.23785
0.2997
0.08275
0.0705
0.08415
0.10495
0.1475
0.5882
0.2076
0.23055
0.0189
0.2006
0.02675
0.11335
0.1322
0.1749
0.154
0.6726
0.11235
0.21585
0.0734
104
0.062314
0.030109
0.086568
0.12928
0.052527
0.358803
0.093666
0.064119
0.018591
0.075999
0.151295
0.579369
0.124592
0.121603
0.0674
0.167097
0.105875
0.066704
0.096838
0.58575
0.055391
0.234375
0.598717
0.202585
0.035184
0.174209
0.108794
0.082003
0.385695
0.103135
0.179217
0.630813
1.003724
0.405993
0.478461
0.125858
0.480834
0.27
0.141954
0.448344
0.118858
0.368953
0.173099
0.184865
0.683803
0.148273
0.265699
0.279651
0.43802
0.543706
0.263139
0.402794
0.131834
0.111999
0.288592
0.215376
0.12459
0.147233
0.190521
0.561567
0.019706
0.154985
0.03406
0.123081
0.313104
0.077735
0.09402
0.039401
0.027303
0.522665
0.078543
0.11915
0.847187
0.265743
0.031689
0.117891
0.019864
0.031275
0.215459
0.043263
0.352908
0.07883
0.140095
0.805657
0.076727
0.051258
0.033789
0.18616
0.099133
0.021646
0.140318
0.030479
0.01845
0.43135
0.1828
0.0676
0.23135
0.21515
0.16305
0.42625
0.19855
0.0752
0.1406
0.0148
0.04345
0.1726
0.237
0.2715
0.2316
0.1117
0.227
0.0681
0.90925
0.0366
0.1613
0.20175
0.06165
0.08265
0.5335
0.0608
0.0662
0.06125
1.02245
0.0929
0.1626
0.09745
0.266
0.3413
0.1795
0.2319
0.08915
0.24675
0.08
0.1256
0.2607
0.36245
0.07545
0.0724
0.05265
0.18105
0.1513
0.276
0.2144
0.2385
0.43175
0.0754
0.0236
0.06205
1.0813
0.15065
0.0384
0.1432
0.0578
0.3923
0.4189
0.9205
105
0.048532
0.886691
0.1914
0.184
0.08805
0.9185
0.13625
0.19375
0.0108
0.5997
0.4619
0.7592
0.1403
0.12185
0.3421
0.08705
0.426
0.29055
0.0601
0.43685
0.63475
0.2474
0.2286
0.02375
0.2585
0.0774
0.1448
0.09795
0.1185