Avian Diversity, Productivity, Survival, and Ecology in the Texas Coastal Bend
by
EVONNE SCHROEDER, B.S.
A Thesis
In
WILDLIFE SCIENCE
Submitted to the Graduate Faculty
of Texas Tech University in
Partial Fulfillment of
the Requirements for
the Degree of
MASTER OF SCIENCE
Dr. Clint W. Boal
Committee Chair
Dr. Selma Glasscock
Dr. Gad Perry
Fred Hartmeister
Dean of the Graduate School
May 2010
Texas Tech University, Evonne Schroeder, May 2010
ACKNOWLEDGMENTS
This project would not have been possible without the funding support of the
Rob and Bessie Welder Wildlife Foundation. I would especially like to thank the
refuge directors, Dr. D.L. Drawe, Dr. Terry Blankenship and Dr. Selma Glasscock, for
their support and assistance. I extend a special thanks to B.C. Glasscock who
“volunteered” extra time and effort to help clear net lanes. I would especially like to
thank my advisor, Dr. Clint Boal, for providing the opportunity to study at Texas Tech
University and for his support of this project. I also thank my committee members:
Dr. Gad Perry and Dr. Selma Glasscock for their input in the creation of this work. I
extend a special thank you to Amy Potts and Brad Strobel who provided essential on
the ground help when I needed it most. Finally, I acknowledge my family, especially
my grandparents, who sent their love in the form of cookies and encouraging letters
and my parents for their love, support and encouragement. Numerous people have
provided support through encouraging words and friendship that it would be
impossible to thank them all by name. Many thanks to all.
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Texas Tech University, Evonne Schroeder, May 2010
TABLE OF CONTENTS
ACKNOWLEDGMENTS ............................................................................................. ii
LIST OF TABLES ..........................................................................................................v
LIST OF FIGURES ..................................................................................................... vii
I.
INTRODUCTION ..............................................................................................1
Introduction .............................................................................................1
Literature Cited .......................................................................................1
II.
AVIAN DIVERSITY AND SPECIES RICHNESS IN TWO VEGETATION
COMMUNITIES IN THE TEXAS COASTAL BEND .....................................2
Abstract ...................................................................................................2
Introduction .............................................................................................3
Methods ...................................................................................................5
Results .....................................................................................................8
Discussion .............................................................................................10
Management Implications .....................................................................12
Literature Cited .....................................................................................12
III.
AVIAN PRODUCTIVITY AND SURVIVORSHIP IN THE TEXAS
COASTAL BEND ............................................................................................24
Abstract .................................................................................................24
Introduction ...........................................................................................25
Methods .................................................................................................27
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Texas Tech University, Evonne Schroeder, May 2010
Results ...................................................................................................30
Discussion .............................................................................................31
Management Implications .....................................................................33
Literature Cited .....................................................................................34
IV.
NESTLING DIETS OF SYMPATRIC GOLDEN-FRONTED (MELANERPES
AURIFRONS) AND LADDER-BACKED (PICOIDES SCALARIS)
WOODPECKERS .............................................................................................45
Abstract .................................................................................................45
Introduction ...........................................................................................46
Methods .................................................................................................48
Results ...................................................................................................50
Discussion .............................................................................................51
Management Implications .....................................................................55
Literature Cited .....................................................................................55
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Texas Tech University, Evonne Schroeder, May 2010
LIST OF TABLES
2.1
Counts of species identified via point counts and mist nets in riparian forest
and shrubland vegetation communities during the breeding seasons of 20072008 on the Welder Wildlife Refuge. ...............................................................20
2.2
Counts of breeding species identified via point counts and mist nets in riparian
forest and shrubland vegetation communities during the breeding seasons of
2007-2008 on the Welder Wildlife Refuge .......................................................22
2.3
Avian community overlap for all species detected by vegetation type
(shrubland and riparian forest) and method (point counts and mist nets) during
2007 and 2008 on the Welder Wildlife Refuge ................................................23
2.4
Avian community richness for breeding species detected and overlap by
vegetation type (shrubland and riparian forest) and method (point counts and
mist nets) during 2007 and 2008 on the Welder Wildlife Refuge ....................23
3.1
Number of captures for all individuals (N) and hatch-year birds (HY) by year
for breeding species during 2007-2009 at Mesquite Pasture and Hackberry
Motte study sites on the Welder Wildlife Refuge, Sinton, Texas .....................38
3.2
Summary of birds (Individuals, Recaptures and Totals) captured from 11 May
to 8 August for 2007, 2008 and 2009 at study sites in shrubland and riparian
forest vegetation communities. .........................................................................39
3.3
Apparent survival estimates (φ) and recapture probabilities (p) for Northern
Cardinals and Painted Buntings derived from capture histories of adult birds on
the Welder Wildlife Refuge during the summers of 2007, 2008, and 2009. ....41
3.4
Candidate models evaluating survival estimates (φ) and recapture probability
(p) parameters for two common species within two vegetation communities on
the Welder Wildlife Refuge. .............................................................................42
3.5
Changes between years in the reproductive index (young/adult) for three
species and all species pooled at two MAPS stations on the Welder Wildlife
Refuge, Sinton, Texas during 2007, 2008, and 2009 ........................................43
3.6
Changes between years in the reproductive index (young/adult) for MAPS
stations across the south-central United States (from DeSante and Kashube
2009) .................................................................................................................44
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Texas Tech University, Evonne Schroeder, May 2010
4.1
Observation start and end dates and total hours for Golden-fronted (GFWO)
and Ladder-backed (LBWO) Woodpecker cavities during summers of 2007,
2008 and 2009 ...................................................................................................61
4.2
Summary of observed prey deliveries by male and female Ladder-backed and
Golden-fronted Woodpeckers to cavity nests at the Welder Wildlife Refuge,
Texas, 2007-2009 ..............................................................................................62
4.3
Total number and percent of prey categories in diets of nestling Ladder-backed
Woodpeckers in the Texas coastal bend. Data collected using video
surveillance at 1 cavity in 2007, 1 cavity in 2008 and 2 cavities in 2009 .........63
4.4
Total number and percent of prey categories in diets of nestling Golden-fronted
Woodpeckers in the Texas coastal bend. Data collected via direct observations
at 1 cavity in 2007 and video surveillance at 2 cavities in 2007 and 1 cavity in
2008 ...................................................................................................................64
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Texas Tech University, Evonne Schroeder, May 2010
LIST OF FIGURES
2.1
Total species richness of shrubland and riparian forest vegetation communities
over two year period (2007–2008) by survey method at the Welder Wildlife
Refuge, Sinton, Texas. ......................................................................................18
2.2
Average species richness detected by survey methods for shrubland and
riparian forest vegetation communities by year (2007 and 2008) at the Welder
Wildlife Refuge, Sinton, Texas .........................................................................19
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CHAPTER I
INTRODUCTION
INTRODUCTION
The collection of data presented in this thesis occurred during the summers of
2007, 2008, and 2009 on the Rob and Bessie Welder Wildlife Foundation Refuge in San
Patricio County, Texas. This study focused on avian ecology and communities in the
Texas coastal bend. The objectives of this study were to assess avian productivity and
survival through operation of two netting arrays, conduct point counts at netting arrays to
estimate species richness and abundance, and monitor nestling diet of sympatric Goldenfronted (Melanerpes aurifrons) and Ladder-backed Woodpeckers (Picoides scalaris).
The following chapters are formatted to facilitate future publications of results
with each chapter written as a stand-alone document. Therefore there may be some
repetition in sections regarding study area, methods, and introduction. These chapters are
the responsibility of the author but in publication will have more than one author. The
following chapters have been formatted to follow author submission guidelines for
publication in the Wilson Journal of Ornithology (Wilson Ornithological Society 2006).
LITERATURE CITED
Wilson Ornithological Society. 2006. Guidelines for authors.
http://www.wilsonsociety.org/documents/wjoguidelines_for_authors.pdf (accessed 3
November 2009).
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CHAPTER II
AVIAN DIVERSITY AND SPECIES RICHNESS IN TWO VEGETATION
COMMUNITIES IN THE TEXAS COASTAL BEND
ABSTRACT
Declining bird populations have been discovered across North America through
the long-term monitoring of the Breeding Bird Survey. The Breeding Bird Survey for
Texas suggests significant declines in a quarter of the surveyed species (n = 160). As
part of a long-term monitoring program, I established banding stations in a riparian forest
and a shrubland vegetation community at the Welder Wildlife Refuge, in San Patricio
County, Texas. Stations were operated once every ten days from 11 May to 8 August
2007 and 2008. Point counts were also conducted during the peak of the breeding season
(mid-May to mid-June) on the day prior to or following netting. Sixty-six total species
were detected through mist nets and point counts. Fifteen species were observed but not
captured, and twenty-six species were captured but not observed. Breeding bird species
richness was greater in the shrubland vegetation community (n = 20) than riparian forest
(n = 16). Of mist net captures in the vegetation communities, more unique species and
total captures were obtained in the shrubland station than the riparian forest station.
Species richness was greatest in the shrubland independent of survey method used.
Vegetation can affect detection and capture of species; therefore, a combination of point
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counts and mist nets may better facilitate intensive monitoring schemes dependent on
research goals.
INTRODUCTION
Declining populations of breeding birds have been reported across the United
States and Canada (Robbins et al. 1989, Askins 1993, Sauer et al. 2007) through longterm monitoring via the Breeding Bird Survey (BBS). Of breeding birds surveyed from
1996-2006, 28% are experiencing a significant negative population trend, and when
combined with those species with nonsignificant negative trends, the percentage
increased to 54% (Sauer et al. 2007). Although attention has been given to the state of
decline in grassland breeding birds (Brennan and Kuvlesky 2005), BBS data indicate
shrubland and woodland breeding birds also show significant declines of 37% and 27%,
respectively (Sauer et al. 2007).
Texas BBS results echo those of the survey-wide census; 25% of surveyed
breeding species experienced significant declining trends from 1966-2006 (Sauer et al.
2007). In 2005, Texas Parks and Wildlife issued the Texas Wildlife Action Plan (TWAP),
which outlined species of concern in the various ecoregions of Texas (Bender et al.
2005). The listing of over 190 avian species in the TWAP illustrates the level of concern
for Texas avifauna. Along with riparian forest habitats, the Gulf Coast Prairies and
Marshes ecoregion is considered a top tier conservation priority for Texas Parks and
Wildlife (Bender et al. 2005). Shrublands have received little conservation attention in
the United States (Askins 2001), and this is reflected in the significant decline in 30% of
shrubland breeding birds in Texas (Sauer et al. 2007).
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The Rob & Bessie Welder Wildlife Foundation Refuge is located within the Gulf
Coast Prairies and Marshes ecoregion of the Texas coastal bend. The refuge provides an
opportunity to monitor avian population trends in a high conservation priority area that is
protected and managed for wildlife conservation. Breeding bird species that occur on the
Welder Wildlife Refuge, such as the Yellow-billed Cuckoo (Coccyzus americanus),
Ladder-backed Woodpecker (Picoides scalaris), Pyrrhuloxia (Cardinalis sinuatus), and
Painted Bunting (Passerina ciris), have shown significant declines in the Texas BBS
from 1966-2006 (Sauer et al. 2007).
To better understand conservation needs of avian species of concern, monitoring
programs are needed to assess avian populations within the Gulf Coast Prairies and
Marshes ecoregion and vegetation communities of concern. Mist net surveys are useful
in sampling and surveying for many species, especially those that may be cryptic or nonvocal, whereas point count data can account for species not normally caught in mist-nets
(Blake and Loiselle 2001, Wang and Finch 2002). Therefore, point counts, when
combined with mist-netting efforts, allow for a more complete assessment of avian
species richness. This combination of survey techniques is recommended for avian
monitoring programs (Dawson et al. 1995, Rappole et al. 1998, Whitman 2004).
The objectives of this study were to (1) estimate avian abundance and species
richness in a riparian forest and a shrubland vegetation community through mist net and
point count surveys and (2) evaluate the efficacy and benefits of these two common
methods of avian population monitoring. Herein, I present the results of a two year study
examining diversity and species richness in two vegetation communities, riparian forest
and shrubland, during the 2007 and 2008 breeding seasons.
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METHODS
Study Area
The Rob and Bessie Welder Wildlife Refuge (3,156 ha) is located approximately
13 km north of Sinton, Texas along the northern edge of San Patricio County in the
coastal bend region of Texas. Average summer temperature is 30o C with average yearly
rainfall totals of 74.4 cm for San Patricio County (Guckian and Garcia 1979). The refuge
consists primarily of shrubland vegetation with a number of live oak and riparian
woodlands.
Within the Welder Wildlife Refuge, I selected two study sites, one each in
riparian forest and shrubland vegetation communities. The first study site was located in
transitional riparian woodland located along the Aransas River. This vegetation
community was characterized by hackberry (Celtis spp.), anacua (Ehretia anacua), cedar
elm (Ulmus crassifolia) and mustang grape (Vitis mustangensis) (Rappole and Blacklock
1985). The second study site was in a shrubland community characterized by mesquite
(Prosopis glandulosa), silver bluestem (Bothriochloa saccharoides), little bluestem
(Schizachyrium scoparium) and lime pricklyash (Zanthoxylum fagara) (Drawe et al.
1978).
Mist nets
I established and operated constant effort mist netting stations within each of the
two study sites during the summers of 2007 and 2008. Netting arrays were situated
opportunistically throughout the mist net stations in locations suitable to catch birds
moving through the habitat (Ralph et al. 1993, DeSante et al. 2009). Each station was
established and operated according to Monitoring Avian Productivity and Survivorship
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(MAPS) guidelines to assess species composition, abundance, survivorship, and
productivity. MAPS stations are operated within ten, 10-day periods with the starting
period dependent upon latitudinal location and when many migrant species will have
already passed through. The two stations were each operated one day during each MAPS
periods 2 through 10, which occur 11 May to 8 August (DeSante et al. 2009). Operation
of nets every ten days prevents local breeding birds from becoming accustomed to net
locations (Burton and DeSante 2004, Faaborg et al. 2004, Ralph et al. 2004). Nets were
opened a half-hour prior to sunrise and closed approximately five or six hours later
depending upon sun exposure. Stations were each comprised of ten 12m long x 2.6m
high, 36mm mesh mist nets. Nets were checked at 20-40 min intervals, depending upon
weather conditions such as gusty or high winds and temperatures over 32oC in the shade.
Captured birds were removed from the net, placed in cotton holding bags, and taken to a
central processing location.
All birds captured were marked with unique numbered aluminum bands from the
USGS Bird Banding Laboratory in accordance with the banding permit. Those birds that
were captured and unable to be banded (e.g. hummingbirds) were processed in the same
way, but with data recorded as an unbanded bird as dictated by MAPS protocol. All birds
were aged and sexed according to Pyle (1997) when age and sex determination
characteristics were able to be determined. Age determinations were based on plumage
characteristics and degree of skull ossification, whereas sex determination was based on
plumage, wing chord, and indicators of breeding condition (i.e., brood patch or cloacal
protuberance). Mass was measured using an electronic scale accurate to 0.1g (Model
HH-320, Ohaus®, Pine Brook, New Jersey). Additional data were recorded, according to
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MAPS protocol, on body fat, body molt, fight feather molt, flight feather wear, and extent
of juvenal plumage.
Point Counts
Point counts are accepted as the standard avian census technique (Verner 1988,
Ralph et al. 1993, Ralph et al. 1995) and conducted in monitoring programs to provide an
index of bird abundance and species richness (Hutto et al. 1986, Petit et al. 1995, Siegel
et al. 2001). To obtain accurate information regarding avian diversity, point counts were
conducted at the MAPS stations, in addition to banding. As the purpose of these counts
was to detect breeding birds by sight or sound, all surveys were conducted at the
beginning of the breeding season (11 May through 19 June), when adults are most
detectable (Ralph et al. 1993). Points were systematically placed 150 meters apart for a
total of nine, 50-meter fixed-radius points within the boundaries of each MAPS station
(Ralph et al. 1993). Surveys were conducted immediately prior to or following the
banding day at that station. Point counts were started at sunrise and continuing until no
later than 10:00 a.m. (Ralph et al. 1993). Counts were 5 minutes in duration (Ralph et al.
1995) and all birds heard or seen in the count radius were recorded along with their
estimated distance from the plot center. Additional data were recorded on birds seen
flying over point count locations but not seen utilizing the area. Birds were identified to
species using visual or aural cues; unidentified individuals were assigned to the most
specific group possible (e.g., unknown Myiarchus flycatcher). Common and scientific
names of bird species follow the American Ornithologists’ Union Check-list of North
American Birds (1998).
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Analyses
I used Sorensen’s similarity coefficient (Ss) to examine similarity between
methods (point count and mist net surveys) and between vegetation communities
(shrubland and riparian forest) calculated from the formula Ss = 2a / (a + b + c) where a =
number of species at both site A and B; b = number of species at site A only; c = number
of species at site B only (Krebs 1998). Sorensen’s similarity coefficient (SSC) values are
interpreted as the proportion of species in common between sites or methods. A SSC
index of 1 indicates that species are the same at both sites, whereas an index of 0
indicates no species in common occur between the sites. I used t-tests to calculate
differences in species richness (i.e., species diversity) between the vegetation
communities and estimated by different survey methods.
RESULTS
Species composition varied within vegetation communities by survey method
(Fig. 2.1) and by year (Fig. 2.2). A total of 66 species were seen, heard, or captured
through mist net and point count surveys (Table 2.1). Of these, 15 species were observed
on point counts, but not captured, and 26 species were captured in mist nets, but not
observed on point counts. In the shrubland, 26 species were observed on point counts
and 38 species were captured in netting arrays; while in the riparian forest 25 species
were observed on point counts and 29 species were captured in netting arrays. A total of
40 species were captured or observed in riparian forest and 46 species were captured or
observed in shrubland. Species richness estimated from mist net captures differed
significantly between the two vegetation communities (t = 2.11, df = 17, P < 0.001), but
not within communities between years (shrubland, t = 2.31, df = 8, P = 0.38; riparian
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Texas Tech University, Evonne Schroeder, May 2010
forest, t = 2.31, df = 8, P = 0.16). Species richness estimates based on point counts were
not significantly different between the two vegetation communities (t = 2.11, df = 17, P =
0.23) or within communities between years (shrubland, t = 2.31, df = 8, P = 0.62; riparian
forest, t = 2.31, df = 8, P = 0.06). Species richness estimates based on mist nets
compared to point counts differed significantly in the riparian forest (t = 2.11, df = 17, P
< 0.001), but were similar in the shrubland community (t = 2.11, df = 17, P = 0.44). Both
vegetation communities had similar numbers of migrant species, with riparian forest
migrants (n = 14) accounting for 33% of captures and shrubland migrants (n = 13)
accounting for 25% of captures. Although shrubland and riparian forest vegetation
communities vary in terms of plant structure, composition, and density, 23 species
detected occurred within both vegetation communities. Of these 23 shared species, only
12 were considered to be resident breeders. A total of 37 breeding species were detected
in the vegetation communities with 21 captured or observed in the riparian forest and 26
captured or observed in the shrubland (Table 2.2).
Sorensen’s similarity coefficient values were similar among all comparisons of
methods and vegetation communities (Table 2.3). Mist net and point count survey
methods had an overlap of 43% of species within each vegetation community. Mist net
surveys always resulted in the greatest diversity of species independent of vegetation
community except for breeding species in the riparian forest (Table 2.4). Examination of
SSC values for breeding species indicate a greater overlap between survey methods
(50%) compared to all detected species. Overlap of breeding species in the two
vegetation communities was 40.7%.
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DISCUSSION
Disadvantages and merits of point counts and mist nets have been discussed
within the literature. Many studies have compared aspects of point counts and mist nets
for wintering (Dawson et al. 1995, Wallace et al. 1996, Gram and Faaborg 1997,
Whitman et al. 1997, Blake and Loiselle 2001, Faaborg et al. 2004) and migratory species
(Dawson et al. 1995, Rappole et al. 1998, Wang and Finch 2002), but few have compared
these methods during the breeding season (Rappole et al. 1993, Dawson et al 1995).
Studies conducted during the breeding season evaluated these methods in “pasture and
forest” communities in Mexico (Dawson et al. 1995) and oak forest in Virginia (Rappole
et al. 1993). This study examined differences between the results produced by these
methods within shrubland and riparian forest communities in the Texas coastal bend.
Regardless of season or vegetation communities, no single method best surveyed the
avian community.
Detection and capture of avian species varies according to a suite of factors.
These include observer detection and identification biases, structure of the vegetation
community, and bird behavior which varies by season and species. More species were
detected with mist nets, regardless of vegetation community, than were detected on point
counts. This is likely due to the presence of late migrants captured in netting arrays that
went undetected during point counts due to their quiet behavior while away from the
breeding grounds; point counts are dependent upon brief aural or visual cues for species
detection and identification. Of the 26 species detected by only mist nets, 19 were
migrants. Some species that would not likely be encountered in mist nets because of their
size and behavior (e.g., Wild Turkey Meleagris gallopavo, Cattle Egrets Bubulcus ibis,
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Greater Roadrunner Geococcyx californianus). These were only detected during point
counts. Therefore, limitations of survey methods should be acknowledged, and use of
both methods should provide a more complete census of the avian community.
Species richness was greatest in shrubland regardless of survey method used
(Figure 2.1). Average species richness detected by the two methods was significantly
different within the forest, but not the shrubland. This is likely a reflection of the
vegetation structure and the ability of the survey methods to accurately sample the
species of the riparian forest avian community. For example, Yellow-billed Cuckoos in
the riparian forest were regularly observed on point counts, though often heard on netting
days, were never captured in mist nets. As this species regularly forages in the forest
canopy above net height of 2.6m (Hughes 1999), mist net captures were unlikely.
However, Yellow-billed Cuckoos were regularly captured in shrubland nets since net
height was closer to the maximum height of the vegetation in this community. Faaborg et
al. (2004) suggests mist-netting results may be most accurate in areas with “short,
scrubby” vegetation. Though not recommended according to MAPS protocols (DeSante
et al. 2009), canopy nets, in addition to ground level nets, may improve sampling of the
forest avian community via mist nets (Jenni et al. 1996, Bonter et al. 2008). Overlap SSC
values for mist net and point count surveys for breeding species was 0.526 for shrubland
and 0.511 for riparian forest. Although the overlap of the avian community among
survey methods was higher among breeding species, about 50% of the resident species
would be overlooked using a single method.
A combination of point count and mist net surveys may better facilitate intensive
avian monitoring schemes due to detection limitations of each survey method. Point
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Texas Tech University, Evonne Schroeder, May 2010
counts are often favored as an inexpensive alternative to more costly and intensive
studies using mist nets. However, long-term mist net monitoring usually provides
additional data, such as population demographics (see next chapter), unavailable through
point count surveys. Monitoring demographic parameters of productivity and
survivorship provide additional information for discerning the patterns of avian declines
and are important data for conservation and management planning. Additionally, mist
nets run by properly trained and permitted personnel have the auxiliary benefit of serving
as a tool for public education programs regarding avian conservation (Hansrote 1996).
MANAGEMENT IMPLICATIONS
This study indicates the benefits of using two survey methods, point counts and
mist nets, to assess avian populations. Operating two banding stations, in addition to
conducting point counts, would be labor intensive for the Welder Wildlife Foundation,
therefore a focus on one vegetation community may best suit the needs of the
Foundation. Shrublands constitute the majority of vegetation on the Rob and Bessie
Welder Wildlife Foundation Refuge. Therefore, continuation of the shrubland netting
array would be most beneficial to understanding the breeding avian community across the
refuge. Continuation of the rotating burn schedule would help maintain the open habitat
structure needed by the shrubland-nesting avian community. In addition to surveying
during the breeding season, this netting array could also be used to monitor the wintering
shrubland avian community.
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DeSante, D. F., K. M. Burton, P. Velez, D. Froehlich, and D. Kaschube. 2009. MAPS
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Krebs, C. J. 1998. Ecological methodology. 2nd edition. Addison-Wesley Educational
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Droege, Editors). Pacific Southwest Research Station, Albany, California, USA.
Ralph, C. J., G. R. Geupel, P. Pyle, T. E. Martin, and D. F. DeSante. 1993. Handbook of
field methods for monitoring landbirds. General Technical Report PSW-GTR144. Pacific Southwest Research Station, Forest Service, U.S. Department of
Agriculture, Albany, California, USA.
Ralph, C. J., S. Droege, and J. R. Sauer. 1995. Managing and monitoring birds using
point counts: standards and applications. Pages 161−169 in Monitoring Bird
Populations by Point Counts (C. J. Ralph, J. R. Sauer, and S. Droege, Editors).
Pacific Southwest Research Station, Albany, California, USA.
Ralph, C. J., E. H. Dunn, W. J. Peach, and C. M Handel. 2004. Recommendations for the
use of mist nets for inventory and monitoring of bird populations. Studies in
Avian Biology 29:187−196.
Pyle, P. 1997. Identification Guide to North American Birds, Part I. Slate Creek Press,
Bolinas, California, USA.
Rappole, J. H., and G. W. Blacklock. 1985. Birds of the Texas Coastal Bend. Texas
A&M University Press. College Station, Texas, USA.
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Rappole, J. H., W. J. McShea, and J. Vega-Rivera. 1993. Evaluation of two survey
methods in upland avian breeding communities. Journal of Field Ornithology
64:55−70.
Rappole, J. H., K.Winker, and G. V. N. Powell. 1998. Migratory bird habitat use in
southern Mexico: mist nets versus point counts. Journal of Field Ornithology
69:635−643.
Sauer, J. R., J. E. Hines, and J. Fallon. 2007. The North American Breeding Bird Survey,
Results and Analysis 1966–2006, version 10.13.2007. USGS Patuxent Wildlife
Research Center, Laurel, Maryland. www.mbr-pwrc.usgs.gov/bbs/bbs.html
(accessed 22 October 2009).
Siegel, R. B., D. F. DeSante, and M. P. Nott. 2001. Using point counts to establish
conservation priorities: how many visits are optimal? Journal of Field Ornithology
72:228−235.
Verner, J. 1988. Optimizing the duration of point counts for monitoring trends in bird
populations. Pacific Southwest Forest and Range Experiment Station, Forest
Service, U.S. Department of Agriculture. Berkeley, California, USA.
Wallace, G. E., H. G. Alonso, M. K. McNicholl, D. R. Batista, R. O. Prieto, A. L. Sosa,
B. S. Oria, and E. A. H. Wallace. 1996. Winter surveys of forest-dwelling
neotropical migrant and resident birds in three regions of Cuba. Condor
98:745−768.
Wang, Y., and D. M. Finch. 2002. Consistency of mist netting and point counts in
assessing landbird species richness and relative abundance during migration.
Condor 104:59−72.
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Whitman, A. A., J. M. Hagan, III, and N. V. L. Brokaw. 1997. A comparison of two bird
survey techniques used in a subtropical forest. Condor 99:955−965.
Whitman, A. A. 2004. Use of mist nets for study of neotropical bird communities.
Studies in Avian Biology 29:161−167.
17
Texas Tech University, Evonne
nne Schroeder, May 2010
40
Mist Nets
35
Point Counts
Species Richness
30
25
20
15
10
5
0
Shrubland
Riparian Forest
FIG. 2.1.
Total species richness of shrubland and riparian
iparian forest vegetation
communities over two year period (2007–2008)
(2007 2008) by survey method at the Welder
Wildlife Refuge, Sinton, Texas.
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Texas Tech University, Evonne Schroeder, May 2010
8.0
Mist Nets
7.0
Average Number of Species
Point Counts
6.0
5.0
4.0
3.0
2.0
1.0
0.0
Shrubland
2007
Riparian Forest
2007
2008
2008
FIG. 2.2.
Average species richness detected by survey methods for shrubland and
riparian forest vegetation communities by year (2007 and 2008) at the Welder Wildlife
Refuge, Sinton, Texas.
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Texas Tech University, Evonne Schroeder, May 2010
TABLE 2.1.
Counts of species identified via point counts and mist nets in riparian forest and
shrubland vegetation communities during the breeding seasons of 2007-2008 on Welder Wildlife
Refuge.
Mist Nets
Species
Acadian Flycatcher
Ash-throated Flycatcher
Audubon's Oriole
Bewick's Wren
Black-and-white Warbler
Blackburnian Warbler
Black-crested Titmouse
Blue-gray Gnatcatcher
Bronzed Cowbird
Brown-crested Flycatcher
Brown-headed Cowbird
Buff-bellied Hummingbird
Bullock's Oriole
Canada Warbler
Carolina Chickadee
Carolina Wren
Cattle Egret
Chestnut-sided Warbler
Common Ground Dove
Common Yellow-throat
Dickcissel
Eastern Wood-Pewee
Golden-fronted Woodpecker
Gray Catbird
Great Egret
Great Kiskadee
Greater Roadrunner
Great-tailed Grackle
Green Jay
Green Kingfisher
Inca Dove
Ladder-backed Woodpecker
Point Counts
Riparian Forest
Shrubland
Riparian Forest
Shrubland
5
1
3
9
1
3
2
5
2
20
2
6
2
1
1
1
1
1
1
3
1
3
10
7
1
2
2
4
2
3
3
3
2
5
13
2
7
25
3
1
2
3
6
1
2
2
3
2
14
8
8
25
1
2
2
6
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Texas Tech University, Evonne Schroeder, May 2010
TABLE 2.1.
Continued.
Mist Nets
Species
Lark Sparrow
Long-billed Thrasher
Louisiana Waterthrush
Magnolia Warbler
Mourning Dove
Mourning Warbler
Northern Bobwhite
Northern Cardinal
Northern Mockingbird
Olive Sparrow
Olive-sided Flycatcher
Orchard Oriole
Painted Bunting
Pyrrhuloxia
Red-eyed Vireo
Red-shouldered Hawk
Red-winged Blackbird
Ruby-throated Hummingbird
Scissor-tailed Flycatcher
Summer Tanager
Swainson's Thrush
Traill's Flycatcher
Unknown Flycatcher
Unknown Hummingbird
Unk. Myiarchus Flycatcher
Unknown Species
Veery
Verdin
White-eyed Vireo
White-tipped Dove
Wild Turkey
Willow Flycatcher
Yellow-bellied Flycatcher
Yellow-billed Cuckoo
Point Counts
Riparian Forest
Shrubland
Riparian Forest
Shrubland
2
1
1
1
186
3
5
1
13
1
1
9
1
1
3
-
4
1
80
26
4
1
4
55
6
1
4
1
2
4
2
2
1
46
1
16
3
132
1
2
8
3
1
1
3
19
2
2
32
1
7
18
49
27
1
37
6
4
8
1
1
1
18
14
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Texas Tech University, Evonne Schroeder, May 2010
Counts of breeding species identified via point counts and mist nets in
riparian forest and shrubland vegetation communities during the 2007-2008 breeding
seasons on the Welder Wildlife Refuge.
TABLE 2.2.
Species
Ash-throated Flycatcher
Audubon's Oriole
Bewick's Wren
Black-crested Titmouse
Blue-gray Gnatcatcher
Bronzed Cowbird
Brown-crested Flycatcher
Brown-headed Cowbird
Buff-bellied Hummingbird
Carolina Chickadee
Carolina Wren
Common Ground Dove
Dickcissel
Golden-fronted Woodpecker
Great Kiskadee
Greater Roadrunner
Green Jay
Green Kingfisher
Inca Dove
Ladder-backed Woodpecker
Lark Sparrow
Long-billed Thrasher
Mourning Dove
Northern Bobwhite
Northern Cardinal
Northern Mockingbird
Olive Sparrow
Painted Bunting
Pyrrhuloxia
Red-shouldered Hawk
Scissor-tailed Flycatcher
Summer Tanager
Verdin
White-eyed Vireo
White-tipped Dove
Wild Turkey
Yellow-billed Cuckoo
Species Detected
Mist Nets
Riparian
Forest
Shrubland
1
1
1
9
3
1
1
3
10
3
7
2
2
2
20
4
2
3
2
1
1
2
2
4
186
80
26
3
4
5
55
6
2
13
1
9
46
1
16
17
22
22
Point Counts
Riparian
Forest
Shrubland
2
5
13
3
2
2
14
7
25
8
25
2
2
6
1
2
6
1
3
7
18
132
49
27
1
1
37
6
2
8
8
1
19
18
2
2
32
14
18
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Texas Tech University, Evonne Schroeder, May 2010
TABLE 2.3.
Avian community overlap for all species detected within vegetation type
(shrubland and riparian forest) and by method (point counts and mist nets) during 2007 and 2008
on the Welder Wildlife Refuge. Sorensen’s Similarity Coefficient (SSC) values are interpreted as
the proportion of species in common between sites or methods (where 1 = complete overlap; 0 =
no overlap).
Point Counts
Mist Nets
Shared Species
SSC Value
Shrubland
26
38
18
0.439
Riparian Forest
25
30
14
0.406
Method
40
51
25
0.431
Habitat
46
41
24
0.432
TABLE 2.4.
Avian community richness for breeding species detected and overlap by
vegetation type (shrubland and riparian forest) and method (point counts and mist nets) during
2007 and 2008 on the Welder Wildlife Refuge. Sorensen’s Similarity Coefficient (SSC) values
are interpreted as the proportion of species in common between sites or methods (where 1 =
complete overlap; 0 = no overlap).
Point Counts
Mist Nets
Shared Species
SSC Value
Shrubland
20
22
15
0.526
Riparian Forest
18
17
12
0.511
Method
30
29
22
0.543
Habitat
26
21
12
0.407
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Texas Tech University, Evonne Schroeder, May 2010
CHAPTER III
AVIAN PRODUCTIVITY AND SURVIVORSHIP IN THE TEXAS COASTAL BEND
ABSTRACT
Widespread avian population declines have been documented across the United
States and Canada through the Breeding Bird Survey, but causes of these declines are
often undetermined. Monitoring avian vital rates, such as survivorship and productivity,
are essential to understanding conservation needs and dynamics of avian populations.
The Monitoring Avian Productivity and Survivorship program was established as a
continent-wide effort to better understand population trends of avian species and identify
possible factors influencing avian populations. I operated mist netting stations during the
breeding seasons of 2007, 2008, and 2009 in two vegetation communities, shrubland and
riparian forest, to determine productivity and survivorship of resident avian species in the
Texas coastal bend. Capture rates (birds/100 net hours) and numbers of hatch-year birds
were higher in the shrubland but did not statistically differ from those found in the
riparian forest. Productivity indices were not statistically different between the two
vegetation communities (shrubland, 0.6; riparian forest, 0.4; P = 0.368); productivity in
riparian forest decreased consistently throughout this study. Apparent survival estimates
and recapture probabilities were calculated for adult Painted Buntings and Northern
Cardinals using Live Recapture Models in Program MARK. Model AICc weights
indicate little support for site specific influences on survivorship or recapture
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Texas Tech University, Evonne Schroeder, May 2010
probabilities. However, considerable effort must be expended to accumulate sufficient
data to allow meaningful interpretations of population trends. This may be especially
problematic for those species of greatest interest, as their numbers may be low and result
in few recaptures for survival modeling.
INTRODUCTION
Declining populations of breeding birds have been reported across the United
States and Canada (Robbins et al. 1989, Askins 1993, Sauer et al. 2007) through longterm monitoring via the Breeding Bird Survey (BBS). Of breeding birds surveyed from
1966-2006, 28% are experiencing a significant negative population trend and when
combined with those species with nonsignificant negative trends, the percentage
increased to 54% (Sauer et al. 2007). Although attention has been given to the state of
decline in grassland breeding birds (Brennan and Kuvlesky 2005), BBS data indicate
shrubland and woodland breeding birds also show significant declines of 37% and 27%,
respectively (Sauer et al. 2007).
Texas BBS results echo those of the United States BBS census as 25% of
surveyed breeding species experienced significant declining trends from 1966-2006
(Sauer et al. 2007). In 2005, Texas Parks and Wildlife issued the Texas Wildlife Action
Plan (TWAP) which outlined species of concern in the various ecoregions of Texas
(Bender et al. 2005). The listing of over 190 avian species in the TWAP illustrates the
level of concern for Texas avifauna. Furthermore, the Gulf Coast Prairies and Marshes
ecoregion is considered a top tier conservation priority for Texas Parks and Wildlife
along with riparian forest habitats (Bender et al. 2005). Shrublands have received little
25
Texas Tech University, Evonne Schroeder, May 2010
conservation attention in the United States (Askins 2001) and this is reflected in the
significant decline in 30% of shrubland breeding birds in Texas (Sauer et al. 2007).
The Rob & Bessie Welder Wildlife Foundation Refuge is located within an
ecotone of the South Texas Plains and the Gulf Coast Prairies and Marshes ecoregions of
the Texas coastal bend. This provides an opportunity to monitor avian population trends
in a high conservation priority area that is protected and managed for wildlife
conservation. Breeding bird species that occur on the Welder Wildlife Refuge, such as
the Yellow-billed Cuckoo (Coccyzus americanus), Ladder-backed Woodpecker (Picoides
scalaris), Pyrrhuloxia (Cardinalis sinuatus) and Painted Bunting (Passerina ciris), have
shown significant declines in the Texas BBS from 1966-2006 (Sauer et al. 2007).
However, the proximate causes of the declining trends are often unclear.
Mark-recapture based banding studies provide the best opportunity to obtain
population demography information such as age and sex ratios, survivorship and
productivity (Ralph et al. 1993, Dunn and Ralph 2004). Although there are many
disturbances in establishment and monitoring of mist nets, Jennings et al. (2009)
demonstrated the use of mist nets and their associated activity do not negatively affect
reproduction in passerines. Productivity and survival estimates obtained through mistnetting have been shown to be consistent with population changes (DeSante et al. 1999).
In turn, this allows insights as to factors affecting population changes (DeSante 1992,
1998, 2004). Monitoring Avian Productivity and Survivorship (MAPS) program was
designed to identify whether population changes were due to activities on the breeding
grounds that may influence productivity, on the wintering grounds through survivorship,
or both (DeSante et al. 2004). The Institute for Bird Populations (IBP) created the MAPS
26
Texas Tech University, Evonne Schroeder, May 2010
program in 1989. The original program of 16 stations has since grown to over 400
stations across the United States and Canada (DeSante et al. 2009). For the south-central
United States, which includes portions of Kansas, Missouri, Arkansas, Louisiana,
Oklahoma and Texas, IBP pools species across states and vegetation communities for
survival estimates, recapture probabilities, and reproductive estimates (DeSante et al.
2009). Thus, MAPS programs provide beneficial information regarding yearly
productivity estimates and population trends across large regions (Bart et al. 1999).
I assisted the Welder Wildlife Foundation in development of MAPS stations that
could be used as an ecological monitoring tool for resident breeding birds on the Welder
Wildlife Refuge, and as a tool for the foundation’s conservation education program. As
part of this program I collected productivity and survivorship data for breeding birds in
two common vegetation communities of the coastal bend region of Texas during the
breeding seasons of 2007, 2008, and 2009 to assess population demographics of
shrubland and riparian forest avian communities.
METHODS
The Welder Wildlife Refuge (3,156 ha) is located approximately 13 km north of
Sinton, Texas along the northern edge of San Patricio County in the coastal bend region
of Texas. Average summer temperature is 30o C with average yearly rainfall totals of
74.4 cm for San Patricio County (Guckian and Garcia 1979). Two vegetation
communities selected for this project were 1) riparian forest and 2) shrubland. Located
along the Aransas River, Hackberry Motte, was a transitional riparian forest vegetation
community characterized by hackberry (Celtis spp.), anacua (Ehretia anacua), cedar elm
(Ulmus crassifolia) and mustang grape (Vitis mustangensis) (Rappole and Blacklock
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Texas Tech University, Evonne Schroeder, May 2010
1985). A shrubland community was chosen in Mesquite Pasture which was characterized
by honey mesquite (Prosopis glandulosa), silver bluestem (Bothriochloa saccharoides),
little bluestem (Schizachyrium scoparium) and lime pricklyash (Zanthoxylum fagara)
(Drawe et al. 1978).
I established and operated constant effort mist netting stations according to MAPS
guidelines to assess resident bird survivorship and productivity within the two vegetation
communities. Stations are operated one day within ten 10-day periods (1 May to 8
August) with the starting period for the station dependent upon latitudinal location and
timing of northbound passage of migrants (DeSante et al. 2009). For this study, I
operated each station for one day during each MAPS periods 2 through 10, which
occurred annually from 11 May to 8 August (DeSante et al. 2009). Operation of nets
once every ten days allows time between netting to prevent resident breeding birds from
becoming accustomed to net locations and therefore avoiding capture in the future. Mist
nets (n = 10) were 12m long x 2.6m high with 36mm black nylon mesh, and were opened
from a half-hour prior to sunrise until approximately five or six hours later. Netting
arrays were situated opportunistically throughout the core area of the stations in locations
deemed suitable to catch birds moving through the habitat (Ralph et al. 1993, DeSante et
al. 2009). Nets were checked at 20-40 minute intervals dependent upon weather
conditions. Captured birds were extracted from netting, placed in cotton holding bags and
taken to a central processing location.
All birds captured were marked with unique numbered aluminum bands from the
USGS Bird Banding Laboratory; birds that were captured and unable to be banded (e.g.
hummingbirds) were processed as other captures with data recorded as an unbanded bird.
28
Texas Tech University, Evonne Schroeder, May 2010
All birds were aged and sexed according to Pyle (1997) when possible. Age
determinations were based on plumage characteristics (such as shape and wear) and
degree of skull pneumaticization, while sex determination was based on plumage
characteristics, wing chord, and indicators of breeding condition (i.e., brood patch and
cloacal protuberance). Additional data were taken, according to MAPS protocol, on body
fat, body molt, fight feather molt, flight feather wear, extent of juvenal plumage, and
body mass. Body mass was measured using an electronic scale accurate to 0.1g (Model
HH-320, Ohaus®). Common and scientific names of bird species follow the American
Ornithologists’ Union Check-list of North American Birds (1998).
Productivity estimates are based on a reproductive index of a species, the
proportion of hatch-year (HY) birds per resident after hatch-year (AHY) birds caught
(Nur et al. 1999). Live Recaptures Models in Program MARK were used to develop a
priori models (White and Burnham 1999) for two species present at both sites, Northern
Cardinals (Cardinalis cardinalis) and Painted Buntings (Passerina ciris). Only these two
species were encountered enough times (see previous chapter) to provide sufficient
sample sizes of recaptures needed for models. In the null model, survival and recapture
rates were held constant; in the site specific models, survival and recapture were modeled
as a function of the vegetation community where individuals were captured. A global
model was incorporated in order to compare residuals between the fully parameterized
model and the reduced model. Corrected Akaike’s information criterion (AICc) was used
to evaluate candidate models for survival estimates and recapture probabilities. To
eliminate the confounding factor of juvenile dispersal, apparent survival and recapture
29
Texas Tech University, Evonne Schroeder, May 2010
probabilities were estimated using only adults. Apparent survival estimates (φ) and
recapture probabilities (p) are presented with their associated standard error (SE).
RESULTS
Adult population size (all resident breeding species pooled) was highest in 2007
for riparian forest and 2008 in the shrubland and lowest for both stations in 2009 (Table
3.1). Total capture rates (birds per 100 net hours) of individuals were numerically greater
for shrubland than for riparian forest, but was not statistically different between sites (t =
4.30, df = 2, P = 0.242). Total recaptures (n = 117) were higher in riparian forest most
likely due to greater mist net effort due to weather and temperature conditions. The
shrubland nets were affected more by wind, heat and sun exposure than the riparian forest
nets due to the trees providing wind breaks and shading nets from the sun. When
adjusted for effort, recapture rates (birds per 100 net hours) were similar between
shrubland (9.24) and riparian forest (8.55) (Table 3.2). Reproductive Index (HY/AHY)
was highest overall in shrubland (0.6) though not statistically different between
vegetation communities (riparian forest, 0.4; t = 4.30, df = 2, P = 0.368).
Estimates of apparent survival and recapture probabilities were calculated for
Painted Buntings and Northern Cardinals (Table 3.3). AICc weights indicate none of the
models supported site-specific survivorship or recapture probabilities, suggesting the
estimates for these parameters were equivalent between shrubland and riparian forest
(Table 3.4). Constant survival models for Painted Buntings were supported by 0.5128
AICc weight which estimated annual apparent survival at 0.609 (± 0.440) with a
recapture probability of 0.283 (± 0.266). The annual apparent survival estimate for
Northern Cardinals was 0.478 (± 0.141) with a recapture probability of 0.400 (± 0.155).
30
Texas Tech University, Evonne Schroeder, May 2010
Models did not support site specific recapture probability for the riparian forest and
shrubland, therefore the recapture probability estimate within both vegetation
communities was 0.408 (± 0.136).
DISCUSSION
Whereas species composition may vary between vegetation communities, results
from this three-year study indicate that overall apparent survival estimates, recapture
probabilities, and productivity indexes were equivalent between the riparian forest and
shrubland communities in this study area. Survival rate estimates from this study for
Northern Cardinals were lower compared to other MAPS stations in the south-central
United States yet recapture probabilities were higher (DeSante and Kashube 2009).
However, Painted Buntings survival estimates were higher and recapture probabilities
were lower (DeSante and Kashube 2009). This is likely an affect of sample size as the
standard error for Painted Buntings were larger than that for Northern Cardinals.
Recaptures of hatch-year birds in subsequent years was low. Within the scope of this
study, it could not be determined if this was the effect of dispersal of juvenile birds from
the natal area (Greenwood and Harvey 1982, Davis and Howe 1992, Anders et al. 1998)
or an effect of juvenile or overwinter survival (Anders et al. 1997). Recapture sample
sizes of adults and hatch-year birds were insufficient to test between year survival
estimates and recapture probability differences for Painted Buntings or Northern
Cardinals. IBP South-Central Region survival estimates (0.491± 0.088) and recapture
probabilities (0.330 ± 0.096) fall within the standard error of the estimates for this study
(DeSante and Kaschube 2009). Karr et al. (1990) reported an annual survival rate of 0.60
± 0.06 for Northern Cardinals in Maryland which also falls within the standard error
31
Texas Tech University, Evonne Schroeder, May 2010
estimates for DeSante and Kaschube (2009) and this study. Sample size of captures for
survival and recapture probability estimates for this study was insufficient to detect
differences. However, this study encompassed only three years of a program that
requires longer periods of monitoring; continued monitoring of these populations will
provide improved estimates of survival and recapture probabilities and population trends.
Yearly reproductive indices for the avian communities within the two vegetation
communities indicate that productivity was variable in the shrubland but consistently
declining in the riparian forest. Changes in the reproductive index for all captured
species between 2007 and 2008 was positive for shrubland (0.358) and negative for
riparian forest (-0.329), while both experienced negative changes (shrubland, -0.745;
riparian forest, -0.228) between 2008 and 2009 (Table 3.5). This may be explained in
part by the environmental conditions during this study. During the 2007 breeding season,
rainfall was sufficient to flood low lying areas, especially in riparian corridors. This
flood event occurred in July; therefore the flooding probably did not greatly affect
productivity as it likely only affected the renest attempts of individuals with nests in the
low lying areas. At the start of the 2009 breeding season, cumulative precipitation totals
were 14.2 cm below normal for the year (Fernandez 2009). Productivity indices were
lowest at both sites during 2009, possibly caused by reduced food availability from
drought. Avian populations in the riparian forest may be unable to maintain themselves
with this apparent continual decreasing trend in productivity without a source population.
Although no regional data are available for this time period, south-central US MAPS
stations also had periods of decreased productivity for Northern Cardinals, Painted
Buntings, White-eyed Vireos and all species pooled for 2004-2005 and, except for
32
Texas Tech University, Evonne Schroeder, May 2010
Northern Cardinals, again for 2005-2006 (Table 3.6). As fluctuations in avian
populations occur regularly, it is unclear how the severely reduced reproductive indices
seen during this study will affect future productivity without long-term monitoring.
Located within an ecotone of two high conservation priority ecoregions for the
Texas Parks and Wildlife Department, the Gulf Coast Prairie and South Texas Plains
(Bender et al. 2005), the Rob and Bessie Welder Wildlife Foundation Refuge has
documented over 114 avian species within refuge boundaries that are currently listed as
species of concern (Welder Wildlife Foundation 2005, Bender et al. 2005). Though
species of concern may exist in lower population numbers which make estimates of
survival and recapture probabilities fallible, long-term monitoring can provide baseline
data on the stability of the population. Therefore, long-term monitoring of avian
populations through the establishment and continuation of a MAPS station at the Welder
Wildlife Refuge will provide beneficial data regarding avian population dynamics,
including avian productivity and survivorship, in the Texas coastal bend.
MANAGEMENT IMPLICATIONS
Survival estimates and recapture probabilities in this study were greatly
influenced by the number of Northern Cardinals captured, especially in the riparian
forest. Shrubland vegetation community did not show this skew capture bias to a single
species. Therefore, long-term monitoring in the shrubland would provide the most
information on a variety of breeding species and lead to a better understanding of vital
rates of the breeding avian community across the refuge. In addition to productivity,
survival estimates and recapture probabilities, monitoring avian populations in the
33
Texas Tech University, Evonne Schroeder, May 2010
shrubland can also provide data on responses to prescribed burning. However, burn plots
should be conducted after the main breeding season to reduce the impact on productivity.
LITERATURE CITED
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Anders, A. D., D. C. Dearborn, J. Faaborg, and F. R. Thompson, III. 1997. Juvenile
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American Ornithologists’ Union. 1998. Check-list of North American birds, 7th Edition.
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Askins, R. A. 1993. Population trends in grassland, shrubland and forest birds in eastern
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Askins, R. A. 2001. Sustaining biological diversity in early successional communities:
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Bart, J., C. Kepler, P. Sykes, and C. Bocetti. 1999. Evaluation of mist-net sampling as an
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(accessed 10 June 2007).
Brennan, L.A. and W. P. Kuvlesky, Jr. 2005. North American grassland birds: an
unfolding conservation crisis? Journal of Wildlife Management 69:1−13.
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Davis, G. J. and R. W. Howe. 1992. Juvenile dispersal, limited breeding sites, and the
dynamics of metapopulations. Theoretical Population Biology 41:184−207.
DeSante, D. F. 1992. Monitoring avian productivity and survivorship (MAPS): a sharp,
rather than blunt, tool for monitoring and assessing landbird populations. Pages
511−521 in Wildlife 2001: Populations. (D. R. McCullough and R. H. Barrett,
Editors). Elsevier Applied Science, London, England.
DeSante, D. F. and D. R. Kaschube. 2009. The Monitoring Avian Productivity and
Survivorship (MAPS) Program 2004, 2005, and 2006 report. Bird Populations
9:86−169.
DeSante, D. F., D. R. O’Grady, and P. Pyle. 1999. Measures of productivity and survival
derived from standardized mist-netting are consistent with observed population
changes. Bird Study 46 (supplement):S178−188.
DeSante, D. F., and D. K. Roseberg. 1998. What do we need to monitor in order to
manage landbirds? Pages 93−106 in Avian Conservation: Research and
Management, (J. Marzluff and R. Sallabanks, Editors). Island Press, Washington,
DC, USA
DeSante, D. F., J. F. Saracco, D. R. O’Grady, K. M. Burton, and B. L. Walker. 2004.
Methodological considerations of the Monitoring Avian Productivity and
Survivorship (MAPS) Program. Studies in Avian Biology 29:28−45.
DeSante, D. F., K. M. Burton, P. Velez, D. Froehlich, and D. Kaschube. 2009. MAPS
Manual 2009 Protocol: Instructions for the establishment and operation of
constant-effort bird-banding stations as part of the Monitoring Avian Productivity
35
Texas Tech University, Evonne Schroeder, May 2010
and Survivorship (MAPS) program. Institute for Bird Populations Contribution
Number 127. Point Reyes Station, California, USA.
Drawe, D. L., A. D. Chamrad, and T. W. Box. 1978. Plant Communities of the Welder
Wildlife Refuge. Welder Wildlife Foundation Contribution Number 5. Sinton,
Texas, USA.
Dunn, E. H. and C. J. Ralph. 2004. Use of mist nets as a tool for bird population
monitoring. Studies in Avian Biology 29:1−6.
Fernandez, C. J. 2009. Crop weather program: rainfall tool, Version 3.0. Texas AgriLife
Research & Extension Center at Corpus Christi. http://cwp.tamu.edu (accessed 18
November 2009).
Greenwood, P. J. 1980. Mating systems, philopatry, and dispersal in birds and mammals.
Animal Behavior 28:1140−1162.
Guckian, W. J., and R. N. Garcia. 1979. Soil Survey of San Patricio and Aransas
Counties. USDA Soil Conservation Service.
Jennings, S. T. Gardali, N. E. Seavy, and G. R. Geupel. 2009. Effects of mist netting on
reproductive performance of Wrentits and Song Sparrows in central coastal
California. Condor 111:488−496.
Karr, J. R., J. D. Nichols, M. K. Klimkiewicz, and J. D. Brawn. 1990. Survival rates of
birds of tropical and temperate forests: Will the dogma survive? American
Naturalist 136:277−291.
Nur, N., S. L. Jones, and G. R. Geupel. 1999. A statistical guide to data analysis of avian
monitoring programs. Biological Technical Publication BTP-R6001-1999. Fish
and Wildlife Service, U.S. Department of the Interior.
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Pyle, P. 1997. Identification Guide to North American Birds, Part I. Slate Creek Press,
Bolinas, California, USA.
Ralph, C. J., G. R. Geupel, P. Pyle, T. E. Martin, and D. F. DeSante. 1993. Handbook of
field methods for monitoring landbirds. General Technical Report PSW-GTR144. Pacific Southwest Research Station, Forest Service, U.S. Department of
Agriculture, Albany, California, USA.
Rappole, J. H., and G. W. Blacklock. 1985. Birds of the Texas Coastal Bend. Texas
A&M University Press. College Station, Texas, USA.
Robbins, C. S., J. R. Sauer, R. S. Greenberg, and S. Droege. 1989. Population declines in
North American birds that migrate to the neotropics. Proceedings of the National
Academy of Sciences 86:7658–7662.
Sauer, J. R., J. E. Hines, and J. Fallon. 2007. The North American Breeding Bird Survey,
Results and Analysis 1966–2006, Version 10.13.2007. USGS Patuxent Wildlife
Research Center, Laurel, Maryland, USA.
Welder Wildlife Foundation. 2005. Birds of the Welder Wildlife Refuge, San Patricio
County, Texas, USA.
White, G. C., and K. P. Burnham. 1999. Program MARK: Survival estimation from
populations of marked animals. Bird Study 46(supplement):S120−138.
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Texas Tech University, Evonne Schroeder, May 2010
TABLE 3.1. Number of captures for all individuals (N) and hatch-year birds (HY) by
year for breeding species during 2007-2009 at shrubland and riparian forest study sites on
the Welder Wildlife Refuge, Sinton, Texas. Bold italics indicate breeding birds that are
listed as species of concern in the Texas Wildlife Action Plan. Species listed in
alphabetical order.
Shrubland
Species
Ash-throated Flycatcher
Audubon's Oriole
Bewick's Wren
Black-and-white Warbler
Black-crested Titmouse
Blue-gray Gnatcatcher
Bronzed Cowbird
Brown-crested Flycatcher
Brown-headed Cowbird
Buff-bellied hummingbird
Carolina Chickadee
Carolina Wren
Common Ground Dove
Dickcissel
Golden-fronted Woodpecker
Great-crested Flycatcher
Great-tailed Grackle
Green Jay
Green Kingfisher
Ladder-backed Woodpecker
Lark Sparrow
Long-billed Thrasher
Louisiana Waterthrush
Northern Bobwhite
Northern Cardinal
Northern Mockingbird
Olive Sparrow
Orchard Oriole
Painted Bunting
Pyrrhuloxia
Red-winged Blackbird
Scissor-tailed Flycatcher
Summer Tanager
Verdin
White-eyed Vireo
White-tipped Dove
Yellow-billed Cuckoo
Total Captures
Net hours
Birds per 100 net hours
Reproductive Index (HY/AHY)
2007
N HY
1
0
1
0
2
1
1
0
4
0
2
0
2
1
1
0
2
1
1
0
1
0
28
9
4
1
2
1
1
0
23
9
3
1
15
12
7
0
101 36
401.7
25.1 9.0
0.6
2008
N HY
3
0
5
0
2
0
3
0
3
3
3
0
1
0
3
1
32
18
21
15
1
1
3
21
10
1
0
4
0
2
2
1
0
16
12
5
0
130 62
356.3
36.5 17.4
0.9
38
Riparian Forest
2009
N HY
2
0
1
0
2
0
2
0
1
1
3
0
4
31
3
5
1
2
0
21
3
2
1
5
1
1
1
5
3
7
1
90 19
367.8
24.5 5.2
0.3
2007
N HY
1
0
1
0
5
1
2
0
5
0
1
0
1
0
1
0
1
1
88
44
1
1
1
0
3
0
3
0
1
0
115 47
469.6
24.5 10.0
0.7
2008
N HY
2
0
3
1
1
0
2
1
2
1
5
1
1
0
1
0
1
0
58
19
2
2
4
0
7
0
5
0
94
25
485.0
19.4 5.2
0.4
2009
N HY
1
0
1
0
1
0
1
0
4
2
2
0
5
0
50
6
1
0
3
1
4
0
3
0
76
9
413.2
18.4 2.2
0.1
Texas Tech University, Evonne Schroeder, May 2010
TABLE 3.2. Summary of birds (Individuals, Recaptures and Totals) captured from 11
May to 8 August for 2007, 2008 and 2009 at study sites in shrubland and riparian forest
vegetation communities. Species shown in bold italics denote Texas Wildlife Action
Plan Species of Concern.
Shrubland
Riparian Forest
Species
New
Recaps
Total
New
Recaps
Total
Acadian Flycatcher
American Redstart
Ash-throated Flycatcher
Audubon's Oriole
Bewick's Wren
Black-and-white Warbler
Blackburnian Warbler
Black-crested Titmouse
Blue-gray Gnatcatcher
Bronzed Cowbird
Brown-crested Flycatcher
Brown-headed Cowbird
Buff-bellied hummingbird
Bullock's Oriole
Canada Warbler
Carolina Chickadee
Carolina Wren
Chestnut-sided Warbler
Common Ground Dove
Dickcissel
Eastern Wood-Pewee
Golden-fronted Woodpecker
Gray Catbird
Great-crested Flycatcher
Great-tailed Grackle
Green Jay
Green Kingfisher
Indigo Bunting
Ladder-backed Woodpecker
Lark Sparrow
Long-billed Thrasher
Louisiana Waterthrush
2
2
1
1
1
2
1
3
11
5
1
6
2
2
6
2
1
3
3
2
3
2
1
7
-
0
0
0
0
0
1
0
0
1
4
0
0
0
0
0
0
0
0
1
0
0
0
0
0
-
2
2
1
1
1
3
1
3
12
9
1
6
2
2
6
2
1
3
4
2
3
2
1
7
-
6
2
4
7
1
1
3
3
5
2
10
2
7
4
1
1
1
7
1
0
0
0
1
0
0
1
0
0
0
15
0
0
0
0
0
0
1
0
6
2
4
8
1
1
4
3
5
2
25
2
7
4
1
1
1
8
1
39
Texas Tech University, Evonne Schroeder, May 2010
TABLE 3.2.
Continued.
Species
Magnolia Warbler
Mourning Warbler
Northern Bobwhite
Northern Cardinal
Northern Mockingbird
Northern Waterthrush
Olive Sparrow
Olive-sided Flycatcher
Orchard Oriole
Painted Bunting
Pyrrhuloxia
Red-eyed Vireo
Red-winged Blackbird
Ruby-throated Hummingbird
Scissor-tailed Flycatcher
Summer Tanager
Swainson's Thrush
"Traill's" Flycatcher
Veery
Verdin
"Western" Flycatcher
White-eyed Vireo
White-tipped Dove
Willow Flycatcher
Yellow-bellied Flycatcher
Yellow-billed Cuckoo
Capture Totals
Net hours
Birds per 100 net hours
Shrubland
New Recaps Total
4
2
6
1
1
2
4
0
4
79
39
118
30
1
31
5
1
6
1
0
1
4
0
4
57
20
77
6
2
8
3
0
3
9
0
9
2
0
2
2
0
2
1
0
1
5
0
5
15
0
15
1
1
2
1
0
1
1
0
1
32
25
57
1
0
1
1
0
1
19
5
24
350
104
454
1125.8
31.1
9.2
40.3
Riparian Forest
New Recaps Total
1
0
1
1
0
1
164
89
253
1
0
1
4
0
4
8
0
8
1
0
1
1
0
1
13
6
19
2
1
3
1
0
1
10
3
13
1
0
1
1
0
1
3
0
3
274
117
391
1367.8
20.0
8.6
28.6
Note: "Traill's" flycatcher grouping consists of two species that are either Willow or Alder flycatchers and "Western"
Flycatcher is a grouping of Pacific-slope and Cordilleran Flycatchers that were impossible to identify to species.
40
Texas Tech University, Evonne Schroeder, May 2010
TABLE 3.3. Apparent survival estimates (φ) and recapture probabilities (p) for
Northern Cardinals and Painted Buntings derived from capture histories of adult birds
on the Welder Wildlife Refuge during the summers of 2007, 2008, and 2009.
Species
Number of
Survival
Probability
Recapture
Probability
Individuals Captures
φ ± SE
p ± SE
Northern Cardinal
161
185
0.478 ± 0.142
0.400 ± 0.155
Painted Bunting
43
49
0.609 ± 0.440
0.283 ± 0.266
41
Texas Tech University, Evonne Schroeder, May 2010
TABLE 3.4. Candidate models evaluating survival estimates (φ) and recapture
probability (p) parameters for two common species (Northern Cardinal and Painted
Bunting) within two vegetation communities on the Welder Wildlife Refuge.
Northern Cardinal Model
∆AICc
AICw
K
Deviance
φ.p.
0.0000
0.5463
2
14.4796
φ . p site
2.0624
0.1948
3
14.4330
φ site p .
2.0946
0.1917
3
14.4652
φ site p site
4.1887
0.0673
4
14.4119
Painted Bunting Model
∆AICc
AICw
K
Deviance
φ.p.
0.0000
0.2692
2
8.9981
φ . p site
0.1995
0.2436
3
6.6991
φ site p .
0.1995
0.2436
3
6.6991
φ site p site
0.1995
0.2436
3
6.6991
42
Texas Tech University, Evonne Schroeder, May 2010
TABLE 3.5. Changes between years in the reproductive index (young/adult) for three
species and all species pooled at two MAPS stations on the Welder Wildlife Refuge,
Sinton, Texas during 2007, 2008, and 2009.
Reproductive Index
% Change
Species
2007
2008
2009
2007 - 2008
2008 - 2009
SHRUBLAND
Northern Cardinal
Painted Bunting
White-eyed Vireo
All Species Pooled
0.474
0.643
4.000
0.554
1.286
0.909
3.000
0.912
0.107
0.167
1.500
0.167
171.4
41.4
-25.0
64.6
-91.7
-81.7
-50.0
-81.7
RIPARIAN FOREST
Northern Cardinal
All Species Pooled
1.000
0.691
0.487
0.362
0.136
0.134
-51.3
-47.6
-72.0
-62.9
43
Texas Tech University, Evonne Schroeder, May 2010
TABLE 3.6. Changes between years in the reproductive index (young/adult) for
MAPS stations across the South-central United States (from DeSante and Kashube
2009).
Reproductive Index
% Change
Species
2004
2005
2006
2004 - 2005
2005 - 2006
Northern Cardinal
0.626
0.428
0.557
-31.6
24.9
Painted Bunting
0.215
0.185
0.196
-14.2
-18.1
White-eyed Vireo
0.477
0.418
0.346
-12.4
-8.3
All Species Pooled
0.375
0.372
0.349
-0.9
-3.5
44
Texas Tech University, Evonne Schroeder, May 2010
CHAPTER IV
NESTLING DIETS AND PARENTAL CARE OF SYMPATRIC GOLDEN-FRONTED
(MELANERPES AURIFRONS) AND LADDER-BACKED (PICOIDES SCALARIS)
WOODPECKERS
ABSTRACT
Diets of nestling Golden-fronted (Melanerpes aurifrons) and Ladder-backed
(Picoides scalaris) Woodpeckers were examined to assess the ecological overlap of these
species at the Rob and Bessie Welder Foundation Wildlife Refuge, in San Patricio
County, Texas. Video surveillance and direct observations were used to monitor
provisioning rates and identify items delivered by adult woodpeckers to their nestlings.
Observations were made at Ladder-backed Woodpecker cavities (n = 4) for 328 hours ( x
= 89.4 ± 36.5 SE) and at Golden-fronted Woodpecker cavities (n = 4) for 230 hours ( x =
57.4 ± 19.1 SE). Invertebrate prey items were identified to order when possible, and
plant items to species. Food items were grouped into the following categories: animal
matter (adult invertebrates and invertebrate larvae), vegetable matter (berries), other
items (snail shells and rocks) and unknown items. Of identifiable food items, Ladderbacked Woodpecker nestling diets consisted of 100% animal matter, comprised of
invertebrate larvae (99%) and invertebrate adults (1%). Diets of Golden-fronted
Woodpecker nestlings were also high in animal matter (77.5%), with more invertebrate
adults (55%) and fewer invertebrate larvae (27%), but also included vegetable matter
45
Texas Tech University, Evonne Schroeder, May 2010
(16%). In coarse food classification, Morisita’s measure of overlap suggested a 31%
dietary overlap between these two sympatric woodpecker species. Foraging methods
employed by these species may explain the low dietary overlap and may also facilitate
their coexistence.
INTRODUCTION
Declining populations of breeding birds have been reported across the United
States and Canada (Askins 1993, Sauer et. al 2007) through long-term monitoring via the
Breeding Bird Survey (BBS). Survey-wide BBS data indicate 44% of cavity-nesting
species are in decline including ten excavator species (e.g. flickers, woodpeckers and
sapsuckers). Texas BBS results echo these showing similar declines in proportions of
cavity-nesting birds (0.44) and excavator species (0.50).
Golden-fronted (Melanerpes aurifrons) and Ladder-backed (Picoides scalaris)
Woodpeckers have experienced a decline in Texas from 1966 to 2007 according to the
BBS (Sauer et al. 2007) and are currently listed as priority species of concern on the
Wildlife Action Plan for Texas (Bender et al. 2005). They are also the only woodpeckers
to occur year-round at the Welder Wildlife Refuge in the coastal bend region of Texas.
These excavator species provide nesting or roosting locations for secondary cavity users
that are also species of concern, such as breeding Black-crested Titmice (Parus
atricristatus) and wintering American Kestrels (Falco sparverius) (Bender et al. 2005).
Skutch (1950) provided an outline of information that should be included in
detailed life histories of avian species, which includes period of incubation, rate of fooddelivery, types of food, length of nestling period and nest failure causes. There have been
no quantitative studies on aspects of parental care, such as feeding rates, brooding bouts,
46
Texas Tech University, Evonne Schroeder, May 2010
or nest sanitation for either Golden-fronted Woodpeckers or Ladder-backed
Woodpeckers (Husak and Maxwell 1998, Lowther 2001). Parental care tasks, such as
food provisioning and nest sanitation, are often reported among woodpeckers as the
males having the greater role in these tasks (Kendeigh 1952, Kilham 1983, Hawkins and
Ritchison 1996). Although sometimes the investment of parental care is more equally
divided between the pair (Kilham 1983, Lawrence 1966).
Published quantitative diet analyses of Ladder-backed and Golden-fronted
Woodpeckers have only been studied using stomach contents from birds of unreported
ages (Beal 1911). However, diets from stomach analysis can be biased due to
deterioration of samples before processing or from different digestion rates of food items
(Dillery 1965, Coleman 1974, Rosenberg and Cooper 1990). Other studies have
provided observations of the Golden-fronted Woodpecker food items which consist of a
variety of invertebrates (adult and larval forms), fruits, nuts and grains (Bent 1939, Leck
1969, Oberholser 1974, Martin and Kroll 1975, Short 1982, Kujawa 1984, Husak and
Maxwell 1998). In contrast, the bulk of Ladder-backed Woodpecker diet is composed of
larval arthropods (Simmons in Bent 1939, Short 1971). However, these qualitative data
provide little information as to the extent which food items are important in their
respective diets. Nestling diets in avian species are known to vary from adult diets
because of nutritional needs for developing chicks (Johnston 1993, Pechacek and Kristin
2004, Koenig et al. 2008). To address the lack of quantitative information on nestling
diets for Golden-fronted and Ladder-backed Woodpeckers, I conducted a study of
comparative food habits of sympatric Golden-fronted and Ladder-backed Woodpeckers
nesting in the coastal bend region of Texas.
47
Texas Tech University, Evonne Schroeder, May 2010
METHODS
The study site was on the Rob and Bessie Welder Wildlife Foundation Refuge
(3,156 ha) near Sinton, Texas along the northern edge of San Patricio County in the
coastal bend region of Texas. Average summer temperature is 30o C with average yearly
rainfall totals of 74.4 cm for San Patricio County (Guckian and Garcia 1979). Mesquitegrassland mosaic vegetation communities constitute the majority of the vegetation types
on the Welder Wildlife Refuge. This shrubland vegetation community was characterized
by honey mesquite (Prosopis glandulosa), agarita (Mahonia trifoliolata), lotebush
(Ziziphus obtusifolia), granjeno (Celtis pallida), silver bluestem (Bothriochloa
saccharoides), little bluestem (Schizachyrium scoparium) and lime pricklyash
(Zanthoxylum fagara) (Drawe et al. 1978).
This study was conducted during woodpecker breeding seasons from 14 May to 5
July in 2007, 2008 and 2009. Nests were found opportunistically while traveling along
refuge roads and trails, or reported by other researchers and refuge staff. Because of the
lengthy nestling stage for woodpeckers (Yom-Tov and Ar 1993), most nests were found
during this stage.
Contents of accessible cavities were examined with a mirror and flashlight to
determine clutch size and nestling age (Ligon 1970, Jackson 1976, Nilsson 1984) and for
proper analyzation of feeding rates (Lawrence 1966). To prevent a decrease in nest
success caused by flushing adults off the nest, I attempted to examine cavity contents
only when the adults were away from the nest. Statuses of inaccessible cavities were
determined by behavioral cues of adults (Lawrence 1966, Jackson 1976).
48
Texas Tech University, Evonne Schroeder, May 2010
A combination of direct observations and video recordings were used to assess
food deliveries by adult woodpeckers to nestlings at nest cavities. To minimize
disturbance of nesting behavior, direct observations were made with binoculars and
spotting scopes ≥ 10 m from nests but at a distance from which male and female
woodpeckers could be distinguished and the cavity could be viewed without obstruction.
Color video cameras (Model OC-225, Clover Electronics®, Los Alamitos, CA U.S.A.)
were installed adjacent (< 0.5 m) to cavity entrance when monitored cavities reached the
nestling stage. Camera images were recorded using time-lapse VHS recorders (Model
SL820, Security Labs®, Noblesville, IN U.S.A.) programmed to record in 48Hr timelapse mode daily from before sunrise (06:00) to after sunset (20:45). Tapes were
subsequently reviewed for delivery of food items to the cavity.
I grouped food items into the following categories: animal matter (adult
invertebrates and invertebrate larvae), vegetable matter (berries), other items (snail shells
and rocks) and unknown items. Delivered food items were identified to highest possible
degree. Invertebrate adults were identified by the presence of wings or legs but were not
identified to order if key features were not recognizable. I used Morisita’s measure of
overlap to quantify diet similarity between Golden-fronted and Ladder-backed
Woodpeckers calculated with the formula (from Krebs 1998)
C = 2∑ Pij Pik / {∑ Pij [(nij – 1)/(Nj – 1) + ∑ Pik [(nik – 1)/(Nk – 1)]}
where: Pij = proportion resources i is of the total resources used by species j; Pik =
proportion resources i is of the total resources used by species k; Nij = number of
individuals of species j that use resources i; Nik = number of individuals of species k that
use resource category i; Nj, Nk = total number of individuals of each species in sample.
49
Texas Tech University, Evonne Schroeder, May 2010
Morisita’s measure of overlap is considered the most unbiased overlap estimator (Smith
and Zaret 1982). I used t-tests to compare delivery rates by adults and per nestling
provisioning rates between the species.
RESULTS
Observations were made at Ladder-backed Woodpecker cavities (n = 4) for 328
hrs ( x = 89.4 ± 36.5 SE) and at Golden-fronted Woodpecker cavities (n = 4) for 230 hrs (
x = 57.4 ± 19.1 SE) during summers of 2007, 2008 and 2009 (Table 4.1). Prey items (n
= 1902) were identified through direct observations and video observations (Table 4.2).
Overall 76.7% and 53.1% of food items delivered were identifiable for Ladder-backed
and Golden-fronted Woodpeckers, respectively (Table 4.3 and 4.4). Identification of
some prey items was not possible due to adults blocking view of item, backlit or foggy
conditions, or the adults manipulating prey items beyond recognition before bringing
items to the cavity entrance. Of identifiable food items, Ladder-backed Woodpecker
nestling diets consisted of 100% animal matter, comprised of invertebrate larvae (99.5%)
and invertebrate adults (0.5%). Diets of Golden-fronted Woodpecker nestlings were also
high in animal matter (77.5%), with more invertebrate adults (56.3%) and fewer
invertebrate larvae (21.2%), but also included vegetable matter (20.1%). Morisita’s
measure of overlap suggested a 31% overlap in diet of the two sympatric woodpeckers.
There were no sex-specific differences in delivery rates among Golden-fronted
Woodpeckers (t = 3.182, df = 3, P = 0.629) or Ladder-backed Woodpecker (t = 3.182, df
= 3, P = 0.734). Although the overall prey delivery rate for Ladder-backed Woodpeckers
( 3.6 ± 0.4/hr SE) was significantly lower (t = 2.13, df = 7, P < 0.001) than that of
50
Texas Tech University, Evonne Schroeder, May 2010
Golden-fronted Woodpeckers (10.4 ±1.3/hr SE), per nestling provisioning rates were not
significantly different between the species (t = 3.182, df = 3, P = 0.201) (Table 4.2).
DISCUSSION
These results support previous observations on diets of Ladder-backed and
Golden-fronted Woodpeckers. Ladder-backed Woodpeckers generally consume larval
forms of arthropods while Golden-fronted Woodpeckers are more diverse in their diet.
Berries constituted 20.1% of identified Golden-fronted Woodpecker food in my study.
This is low compared to that reported by Beal (1911) for Golden-fronted Woodpecker
(45.3%) and other melanerpine woodpeckers (e.g., Red-bellied Woodpecker (Melanerpes
carolinus) 69.0% and Gila Woodpecker (Melanerpes uropygialis) 60.0%). Although
there were no berries in the Ladder-backed Woodpecker diet in this study, Beal (1911)
reported vegetable matter constituted 7.9% of the species diet based on stomach contents
of 14 individuals. Diets of other closely related woodpeckers of the genus Picoides, such
as the Red-cockaded (P. borealis) and Nuttall’s (P. nuttalli) Woodpeckers, include
approximately 20% vegetable food (Beal 1911).
I also observed Golden-fronted Woodpecker adults provided small rocks and snail
shells as a portion of nestling diets (0.024). Calcium is an important mineral for growing
nestlings (Tilgar et al. 2004, Dawson and Bidwell 2005) and snail shells can provide a
high source of calcium for nestlings (Bures et al. 2000). Adults feeding nestlings grit or
snail shells have not been previously reported for Golden-fronted Woodpeckers, although
it has been observed among other woodpeckers (Williams and Batzli 1979, Koenig et al.
1995, Hanula et al. 2000).
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Texas Tech University, Evonne Schroeder, May 2010
Few studies have examined foraging methods used by Golden-fronted and
Ladder-backed Woodpeckers. Kujawa (1984) states “gleaning, pecking, probing, and
ground foraging” are the main foraging methods for Golden-fronted Woodpeckers.
Although I did not record data on foraging events, in addition to the main foraging
methods noted by Kujawa (1984), I also observed Golden-fronted Woodpeckers flycatching. These foraging techniques are reflected in the diversity of arthropods and fruits
reported in their diet. Foraging methods of Ladder-backed Woodpeckers also are
reflective of their diet, as their main techniques are probing, pecking and prying (Short
1971) which provides access to prey under bark, such as invertebrate larvae.
Morisita’s measure of diet overlap was 31% for this study. Percent of diet
overlap would likely change if unknown items for Golden-fronted and Ladder-backed
Woodpeckers (n = 854 and 284, respectively) could have been identified. In direct
observations, adult Golden-fronted Woodpeckers were observed to manipulate adult
invertebrates prior to arriving at cavity. Manipulated prey items were often fed to
nestlings by the adults making several trips to cavity with portions of large adult
invertebrates. Thus the large number of unknowns may be an artifact of multiple
deliveries of manipulated, and therefore unidentifiable, adult invertebrates and would
thereby increase the number of adult invertebrates in the nestling diet of Golden-fronted
Woodpeckers. Adult invertebrates, although well represented in nestling diets of Goldenfronted Woodpeckers, were lacking in the Ladder-backed Woodpecker observations in
this study. In addition to invertebrate larvae, Beal (1911) reports the stomach contents of
Ladder-backed Woodpeckers contained ants (Hymenoptera: Formicidae) which would be
hard to detect via direct or video observations due to their small size. Unknown items for
52
Texas Tech University, Evonne Schroeder, May 2010
Ladder-backed Woodpeckers tended to be small and held in the bill in a way that
prevented identification. Of adult invertebrates (n = 4) observed for Ladder-backed
Woodpeckers in this study, half (n = 2) were captured by the male while in the cavity.
The results of this study are likely biased to larger or more visible prey items (e.g.
invertebrate larvae), especially for the Ladder-backed Woodpecker. Bill size differences
between Golden-fronted (27.9-35.7mm) and Ladder-backed Woodpeckers (17.522.1mm) (Pyle 1997) may reduce dietary overlap of invertebrates due to the ability of the
two species to capture and manipulate different sized prey items. A more in depth study
with regards to size of prey items or with finer scale classification of prey items to genus
or species level would elucidate more details on dietary overlap.
Although, interspecific competition for food is likely low as suggested by
Morisita’s measure of overlap, competition may exist between these two sympatric
woodpeckers and other secondary-cavity nesting species for cavity locations. Nest sites
did not appear to be limiting in this study as all nests monitored were located in wooden
gate and fence posts or utility poles which were plentiful across the landscape. Although
not quantified in this study, woodpeckers may prefer these poles to other hardwoods
present in area, such as live oak (Quercus virginiana) or mesquite, as poles may be of a
softer wood and therefore easier to excavate cavities. Golden-fronted Woodpeckers
reused nest cavities for multiple broods within the breeding season and the following
years, while Ladder-backed Woodpeckers were not observed to reuse nest cavities the
following breeding season and were single-brooded. The presence of these posts across
the landscape possibly allows the Golden-fronted Woodpecker to be more abundant and
successful in areas without large trees (Husak and Maxwell 2000), though overall
53
Texas Tech University, Evonne Schroeder, May 2010
woodpecker density may decrease as ranchers change from aging wooden posts to
modern metal fences.
The presence of excavator species is essential to the reproductive efforts of
secondary cavity users. In Texas, 44% of surveyed cavity-nesting species show a
declining trend from 1966 to 2007 (Sauer et al. 2007). Several secondary cavity nesting
species, which included Eastern Bluebirds (Sialia sialis), European Starlings (Sturnus
vulgaris), and Brown-crested Flycatchers (Myiarchus tyrannulus), were observed
utilizing previous year or older woodpecker cavities and nest boxes. European Starlings
were the only species observed to impact woodpecker nesting attempts by
commandeering cavities from Golden-fronted Woodpeckers. Aggressive takeover of
woodpecker cavities by European Starlings have been widely reported for Golden-fronted
Woodpeckers (Husak and Maxwell 1998) and other picid species (Shelley 1935; Howell
1943; Ingold 1989; Kerpez and Smith 1990; Ingold 1994, 1996, 1998; Vierling 1998).
Nest boxes could be installed in areas in which wooden fence posts have been removed to
provide additional nesting and roosting locations and ease competition for cavities.
Although Golden-fronted and Ladder-backed Woodpeckers were not observed to have
utilized nest boxes in the area, McComb and Noble (1981) reported that Red-bellied,
Red-headed (Melanerpes erythrocephalus), and Hairy Woodpeckers (Dendrocopus
villosus) will utilize nest boxes in addition to natural cavities.
Monitoring nest boxes through participation in citizen science projects such as
NestWatch can provide educational benefits for school and community groups by
increasing public knowledge and interest about breeding biology of local avifauna. The
standardized protocol for NestWatch provides a structural basis of data collection which
54
Texas Tech University, Evonne Schroeder, May 2010
allows locally collected data to be added to the larger, continent-wide database of nest
survival and success (Philips et al. 2007). Declines in excavator species may impact
populations of secondary cavity-nesting species (Short 1979). Therefore, continual
monitoring of excavator and secondary cavity-nesting species are essential for knowledge
about population fluctuations.
MANAGEMENT IMPLICATIONS
Populations of excavator species, such as Golden-fronted and Ladder-backed
woodpeckers, and secondary cavity-nesters, such as Eastern Bluebirds and Myiarchus
flycatchers require cavities in which to raise their young. Wide use of fence posts and
utility poles by cavity-nesting species shows the influence anthropogenic items placed
across the landscape has on avian populations. As aged fencing will eventually need to
be replaced to meet the needs of landowners, nest boxes placed along fence lines could
diminish the effects of post removal and their associated cavities. Thereby, maintaining
nesting locations for populations of cavity-nesting species.
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Agriculture Biological Survey Bulletin, Number 37:1−64.
Bender, S., S. Shelton, K. C. Bender, and A. Kalmbach. 2005. Texas Comprehensive
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Bent, A. C. 1939. Life histories of North American woodpeckers. United States National
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Howell, A. B. 1943. Starlings and woodpeckers. Auk 60:90−91.
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Husak, M. S., and T. C. Maxwell. 1998. Golden-fronted Woodpecker (Melanerpes
aurifrons). The Birds of North America, Number 373.
Husak, M. S., and T.C. Maxwell. 2000. A review of 20th century range expansion and
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and Red-bellied Woodpeckers and European Starlings. Auk 106:209−217.
Ingold, D. J. 1994. Influence of nest-site competition between European Starlings and
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Kerpez, T. A. and N. S. Smith. 1990. Competition between European Starlings and native
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Koenig, W. D., P. B. Stacey, M. T. Stanback, and R. L. Mumme. 1995. Acorn
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TABLE 4.1. Observation start and end dates and total hours for Golden-fronted
(GFWO) and Ladder-backed (LBWO) Woodpecker cavities during the summers of 2007,
2008 and 2009.
Observation Dates
Year
Cavity #
Species
Start
End
Total Hours
2007
702
GFWO
23-May
24-May
7.0
2007
702B
GFWO
28-Jun
5-Jul
99.8
2007
704B
GFWO
21-Jun
1-Jul
64.9
2007
720
LBWO
20-Jun
28-Jun
120.6
2008
842
LBWO
14-May
9-Jun
56.7
2008
845
GFWO
13-Jun
17-Jun
57.9
2009
960
LBWO
9-Jun
26-Jun
173.7
2009
961
LBWO
2-Jun
3-Jun
6.6
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Texas Tech University, Evonne Schroeder, May 2010
TABLE 4.2. Summary of observed prey deliveries by male and female Ladder-backed and Golden-fronted Woodpeckers
to cavity nests at the Welder Wildlife Refuge, Texas, 2007-2009.
Ladder-backed Woodpecker
Golden-fronted Woodpecker
Male
Female
Both
Male
Female
Both
Invertebrate Larvae
519
414
993
67
137
205
Adult Invertebrate
2
2
4
300
24
543
Vegetable Matter
0
0
0
112
82
194
Other Items
0
0
0
11
12
23
Unknown Items
129
154
284
412
423
854
Prey Deliveries
650
570
1221
902
878
1819
1.94(0.46)
1.70(0.24)
3.63(0.36)
5.03(0.54)
5.19(0.80)
10.37(1.29)
Deliveries Per Hour (SE)
Per Nestling Per Hour
1.08(0.15)
62
3.11(1.15)
Texas Tech University, Evonne Schroeder, May 2010
TABLE 4.3. Total number and percent of prey categories in diets of nestling Ladder-backed Woodpeckers in the Texas coastal
bend. Data collected using video surveillance at 1 cavity in 2007, 1 cavity in 2008, and 2 cavities in 2009.
Invertebrate
Larvae
Adult
Invertebrates
Vegetable
Matter
N
%
N
%
N
%
N
%
N
%
Subtotal
Cavity 720
280
73.11
4
1.04
0
0.00
0
0.00
99
25.85
383
Cavity 842
153
60.24
0
0.00
0
0.00
0
0.00
101
39.76
254
Cavity 960
475
85.13
0
0.00
0
0.00
0
0.00
83
14.87
558
Cavity 961
25
96.15
0
0.00
0
0.00
0
0.00
1
3.85
26
Other
Unknown
Total
Subtotal
933
76.41
4
0.33
0
0.00
63
0
0.00
284
23.26
1221
Texas Tech University, Evonne Schroeder, May 2010
TABLE 4.4. Total number and percent of prey categories in diets of nestling Golden-fronted Woodpeckers in the Texas coastal
bend. Data collected via direct observations at 1 cavity in 2007 and video surveillance at 2 cavities in 2007 and 1 cavity in 2008.
Invertebrate
Larvae
Adult
Invertebrates
Vegetable
Matter
N
%
N
%
N
%
N
%
N
%
Subtotal
Cavity 702B
97
20.46
132
27.85
2
0.42
1
0.21
242
51.05
474
Cavity 704B
70
11.84
187
31.64
70
11.84
10
1.69
254
42.98
591
Cavity 702
18
20.22
28
31.46
21
23.60
0
0.00
22
24.72
89
Cavity 845
20
3.01
196
29.47
101
15.19
12
1.80
336
50.53
665
Other
Unknown
Total
Subtotal
205
11.27
543
29.85
194
10.67
64
23
1.26
854
46.95
1819