AN ABSTRACT OF THE THESIS OF
Eric V. Rickerson for the degree of Master of Science in Wildlife Science presented
on July 23, 2001. Title: Nesting Ecology of Mallards in the Willamette Valley of
Oregon.
Redacted for Privacy
Abstract approved:
Although widely studied in many portions of North America, little is known
about the specific habitat requirements of mallard ducks (Anasplatyrhynchos) during
the breeding season in western Oregon. I radio-marked 72 female mallards in the
Willamette Valley of Oregon in March-April 1995-96 to document wetland habitat
selection during pre-nesting and nesting phases, nesting cover selection, nesting and
female success rates, nesting chronology, and survival of females during the pre-
nesting and nesting periods. Wetland habitat selection was higher for seasonal
riverine and permanent lacustrine habitats during the pre-nesting and nesting periods.
Uncultivated upland and wetland habitat nesting sites with a strong cover component
had a higher selection ranking compared to agricultural cropland and ash-cottonwood
riparian. The reproductive period was 107 days beginning in early-March and
concluding in late-June with the peak of nest attempts occurring around May 9.
Nesting effort was low with 38.4% of females failing to attempts at least one nest.
Nest survival probabilities ranged from 0.106 in 1995 to 0.216 in 1996 with a pooled
estimate of 0.186 (95% C.I.=0.122-0.298). Mammalian predation accounted for 84%
of nest failures. Overall female success was 40.5% and differed between first year
(SY) and second year and older females (ASY). Female survival probabilities ranged
from 0.5 11 in 1995 to 0.733 in 1996, with a pooled estimate of 0.668 (95%
C.I.=0.5370.842).
©Copyright by Eric V. Rickerson
July 23, 2001
All Rights Reserved
Nesting Ecology of Mallards in the Willamette Valley of Oregon
by
Eric V. Rickerson
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Master of Science
Presented July 23, 2001
Commencement June 2002
Master of Science thesis of Eric V. Rickerson presented on July 23, 2001
APPROVED:
Redacted for Privacy
Maj or Professoi, representing
ii. lif-4 ience
Redacted for Privacy
Head of the Department of Fisheries an& Wildlife
Redacted for Privacy
Dean of Graduate Scjd
I understand that my thesis will become part of the permanent collection of Oregon
State University libraries. My signature below authorizes release of my thesis to any
reader upon request.
Redacted for Privacy
Eric V. Rickerson, Author
ACKNOWLEDGMENTS
This project would not have been possible without the assistance and support
of many individuals. It was truly a joint effort, and my deepest thanks go to those who
gave much time and effort to bring this research project to completion. First, I wish to
thank my advisor Dr. Robert L. Jarvis whose guidance and incredible patience proved
invaluable through this research. I really enjoyed the many times I spent picking his
brain concerning his understanding of the mallard, and where we need to go from
here. I would also like to thank graduate committee members Boone Kauffman and
Cliff Pereira for their assistance throughout the project. I am grateful to Derek
Mynear, Kyle Green, and Jeff Gruber who helped me collect field data.
Funding for this project was provided by the Oregon Department of Fish and
Wildlife (ODFW), Oregon Duck Hunters Association, Safari Club International
Portland Chapter, and the California Department of Fish and Game. In particular, I
wish to thank ODFW Migratory Game Bird Biologist Brad Bales who was
instrumental in getting the project off the ground. Many thanks to Dave Budeau and
the staff at E.E. Wilson Wildlife Area for the use of equipment and their willingness to
assist me whenever possible. I would also like to thank all the participating
landowners who provided access to their properties and insight into the habits of
mallards in their backyards.
To Jeff, Robyn, James, and Janelle Rice, my second family. I would like to
express my deepest gratitude and love to you for all your support before, during, and
after the project. Without your incredible generosity, I would not have been able to
undertake this project. I am truly blessed to be a part of your family.
I express my gratitude to my mother, brothers, and sister for their love,
support, and influence that enabled me to succeed throughout my life.
To Jake, because of your unconditional love and presence in my life, especially
during the early years of this project, you helped me overcome adversity and allowed
me to see that the little things are what matters. I love you very much.
Finally, I am indebted my to wife Kayla. Words miserably fail to express my
gratitude to her for her endless support. I simply would not have completed this
project without her. Any good thing that has come of this work must be largely to her
credit. The greatest satisfaction I have is in joyfully sharing my love and life with her.
TABLE OF CONTENTS
Page
INTRODUCTION
1
STUDY AREA
4
METHODS
7
STUDY DESIGN
7
CAPTURE, MARKING AND MONITORING
7
HABITAT SAMPLING
9
REPRODUCTIVE BIOLOGY
11
DATA ANALYSIS
13
RESULTS
15
CAPTURE, MARKING AND MONITORING
Habitat Use and Selection
Home Range Sizes
Wetland Selection
Nesting Habitat Selection
Nest Site Characteristics
REPRODUCTIVE BIOLOGY
Nesting Effort
Nesting Chronology
Nest Survival
Female Success
Female Survival
NEST SUCCESS-HABITAT RELATIONSHIPS
DISCUSSION
HABITAT SELECTION
15
16
16
17
19
21
21
21
22
24
28
28
32
36
36
TABLE OF CONTENTS (Continued)
Page
Home Range Sizes
Wetland Selection
Nesting Habitat Selection
Nest Site Characteristics
REPRODUCTIVE BIOLOGY
Nesting Effort
Nesting Chronology
Nest Survival
Female Success
Female Survival
NEST SUCCESS-HABITAT RELATIONSHIPS
36
38
41
43
46
46
47
50
52
54
56
MANAGEMENT AND RESEARCH IMPLICATIONS
57
LITERATURE CITED
62
APPENDICES
73
APPENDIX A. Habitat community type description in the
Willamette Valley of Oregon (from Kagan
and Caicco 1992)
APPENDIX B. Plant species recorded within 1 meter radius
of mallard nests in the Willamette Valley
of Oregon, 1995-96
74
79
LIST OF FIGURES
Page
Figure
Study area, trapping and nest site locations of mallard
nesting ecology research in the Willamette Valley of
Oregon, 1995-1996
6
Nest initiation and hatching chronology of radio-marked female
mallard nests (n=85) in the Willamette Valley of Oregon, 1995-96
23
Number of successful and unsuccessful mallard nests (n=85)
by plant community type (Kagan and Caicco 1992) in the
Willamette Valley of Oregon, 1995-96
27
Predicted probability and observed nest success by mallards in the
Willamette Valley of Oregon, 1995-96, as a function of horizontal
cover values (0-4). Hosmer and Lemeshow Goodness-of-Fit
Statistic = 9.446 with 6 d.f.; p = 0.149
35
LIST OF TABLES
Page
Table
Habitat characteristics recorded at mallard nests in
the Willamette Valley of Oregon, 1995-96
10
Home range size of radio-marked pre-nesting female mallards
in the Willamette Valley of Oregon, 1995-1996
16
Mean difference among ranks and selection rank of
wetland classes used within home ranges of sixty-two
female mallards during pre-nesting and nesting periods in the
Willamette Valley of Oregon, 1995-1996
18
Mean wetland habitat available and use within home ranges
of sixty-two female mallards during pre-nesting and nesting
periods in the Willamette Valley of Oregon, 1995-96
18
Mean difference among ranks and selection rank of nesting habitats
within thirty-nine female mallard home ranges in the Willamette
Valley of Oregon, 1995-96
20
Mean nesting habitat available and use within home ranges of
thirty-nine female mallards in the Willamette Valley
of Oregon, 1995-96
20
Nesting effort of radio-marked female mallards in the Willamette
Valley of Oregon, 1995-96
22
Fate of 86 mallard nests in the Willamette Valley of
Oregon, 1995-96
25
Mayfield survival rates of radio-marked and incidental mallard
nests in the Willamette Valley of Oregon, 1995-96
26
Percent of radio-marked female mallards with a successful nest in
one of their attempts in the Willamette Valley of Oregon, 1995-96
28
Daily and breeding season (March-June) survival rates of radiomarked female mallards in the Willamette Valley of Oregon,
1995-96
30
LIST OF TABLES (Continued)
Table
Page
Drop-in deviance F-test for vegetation and physical habitat
characteristics of successful mallard nests in the Willamette
Valley of Oregon, 1995-96
33
Final logistic regression model for vegetation and physical
habitat characteristics of successful mallard nests in the
Wiflamette Valley of Oregon, 1995-96. Hosmer and Lemeshow
Goodness-of-Fit Statistic 9.466 with 6 d.f. (p=O.l49)
34
Nesting Ecology of Mallards in the Willamette Valley of Oregon
INTRODUCTION
Impacts to mallard population recruitment may occur at any number of points.
However, limitations usually occur as: 1) deficiencies in pre-nesting and nesting
habitat, 2) low nest success, or 3) low duckling survival (Cowardin et al. 1985).
During the pre-nesting period breeding pairs disperse to small shallow wetlands. In
addition to utilization of all available habitat, dispersal provides females the isolation
needed to acquire nutrients necessary for egg production and energy reserves needed
for attentive incubation (Krapu et al. 1983). Small, shallow, farmed/tilled wetlands
produce abundant aquatic macro-invertebrates. These foods are high in protein, easily
digested and are sought by pre-nesting female mallards (Swanson et al. 1985). The
small size of these ponds makes them easily defended by the male which allows the
female to forage unmolested. Abundance and distribution of these small wetlands
among suitable upland nesting cover and other types of more permanent wetlands are
important factors determining potential productivity of breeding mallard populations.
Nest success is a major component of annual mallard productivity. In the
Prairie Pothole Region, Greenwood et al. (1987) estimated only 15% nest success was
needed to perpetuate the population, yet they rarely found nest success that high in the
predator rich prairies. Many predators consume duck eggs and predation is usually the
greatest cause of nest failure (Cowardin and Johnson 1979). Alteration of native
landscapes in North America has generally favored small to medium sized predators
2
and scavengers with broad habitat and food requirements that commonly consume
duck eggs (Johnson and Sargeant 1977, Sargeant et al. 1984).
Western Oregon supports a large and varied community of predators and
scavengers creating a high potential for nest failures. However, re-nesting
opportunities could be extended in the mild weather of western Oregon, which could
compensate for low nest success rates. Additionally, many investigators have
demonstrated that nest success is directly related to extent and density of upland
nesting cover (Kirsch et al. 1978, Livezey 1981, Cowardin et al. 1985, Sugden and
Beyersbergen 1986, 1987). Compared to semi-arid western marshes of the Great
Basin and the Prairie Pothole Region, vegetative cover in western Oregon is extensive
and dense. Dense potential nesting cover may ameliorate effects of a large
community of predators and scavengers. However, the linear arrangement of much of
the dense nesting cover in western Oregon may not provide much protection for duck
nests.
Rapid drying of shallow wetlands in late spring and early summer could
jeopardize survival of ducklings. However, little is known about nesting chronology
in western Oregon to speculate about annual wetland cycles as limitations on mallard
production.
The Willamette Valley is intensely utilized for a variety of resources, of which
agriculture is predominant. Such uses have altered the valley environment, and
agricultural practices may have important consequences for mallards. For instance,
breeding mallards are sensitive to disturbance (Higgins 1977). Regulation of land use
3
activities to minimize disturbance during the nesting season may be beneficial to
mallards. Unfortunately, very little is known about how mallards use wetland and
nesting habitat resources in the Willamette Valley.
This project was designed to investigate and provide information on nesting
ecology and habitat use of breeding mallard females in the Willamette Valley of
Oregon. Primary objectives of this study were: 1) determine wetland habitat selection
during pre-nesting and nesting phases of the mallard reproductive cycle in western
Oregon; 2) determine nest site characteristics and nesting cover selection by mallards;
3) determine nesting and female success rates; 4) determine nesting chronology, and;
5) determine survival of females during the pre-nesting and nesting periods.
4
STUDY AREA
The study was conducted in a 1544 km2 area of the southcentral Willamette
Valley of Oregon (44° 25' 44° 57' N, 123° 14' - 123° 22' W) (Fig. 1). The
Willamette Valley is situated between the Coast Range mountains to the west and the
Cascade Range mountains to the east with interspersed groups of low hills (Franklin
and Dryness 1988). The valley floor is approximately 6,400 km2 and is bisected north
to south by the Willamette River.
The climate of the valley is a modified, maritime temperate regime
characterized by cool, wet winters and warm, dry summers. Annual rainfall averages
100 cm, with approximately 10 % occurring between May and September (Franklin
and Dryness 1988). Annual temperatures range from 4.0 to 18.9° C, with an average
annual temperature of 11.3° C. Elevations in the study area range from 50 to 250
meters above sea level.
The study area was located in the Pinus-Quercus-Pseudotsuga zone extending
approximately 380 km from Portland south to Cottage Grove (Franklin and Dryness
1988). The vegetational mosaic includes oak woodlands, coniferous forests,
grasslands, and sclerophyllus shrubs classified into 15 community types (Kagan and
Caicco 1992).
The Willamette Valley was settled during the middle of the l9 century and
has been subjected to extensive human influences. Cities, farmlands and other
developments dominate the landscape and the area holds
70% of the state's human
5
population (2.14 million in 1995). The valley has approximately 1.3 million acres of
agricultural land, primarily in annual and perennial grass production. Two urban
centers (Corvallis and Albany) with populations> 50,000 people, one state managed
wildlife area (EE Wilson - 1,693 acres) and portions of two federal national wildlife
refuges (Baskett Slough - 2,492 acres and W. L. Finley - 5,325 acres) were within the
study area.
6
Baskett Slough NWR\\
+
onmouth
A
+
Luckiamute River
+
A
BA
A
A
EFA
Wilson
idlife Areaf
V-
'p
A
+
A
0 Alban
+
+
A
Trapping sites
Corva
Hwy 34
S
1995 Nest Site
AEB
A 1996 Nest Site
A?A
Aâf
A4EBA
+
0
LW.
Finley NWR
5
10
Kilometers
Figure 1. Study area, trapping and nest site locations of mallard nesting ecology
research in the Willamette Valley of Oregon, 1995-1996.
7
METHODS
STUDY DESIGN
Radio telemetry was used to gather information (via repeated observations on
marked individuals) on the movements, nest site locations, wetland and nesting habitat
use, and breeding chronology of mallards. From March through mid-June the
emphasis was to capture females and document wetland and nesting habitat use in
relation to availability, and locate nests. Nests were examined for success or failure,
and nest site characteristics were measured.
CAPTURE, MARKING AND MONITORING
The study area was surveyed during late-February and early-March 1995 and
1996 to locate mallard pairs using farmed/tilled and seasonal wetlands. Pairs were
observed for
days to determine if the pair was a resident breeding pair or a
transient (migrant) pair. A resident breeding pair was defined as a mallard pair
exhibiting territorial behavior (aggression toward conspecifics) at a specific location
for> 3 days. When a resident breeding pair was located, a live mallard female-decoy
trap (Sharp and Lokemoen 1987) was placed at the location where the breeding pair
was observed. Decoy trapping for pre-laying female mallards was conducted from
mid-March through mid-April at 21 trapping locations distributed across the study
8
area. Trapping sites were non-randomly distributed according to landowner
cooperation and trap-site accessibility.
All captured mallards were fitted with U.S. Fish and Wildlife Service leg
bands. Females were aged as 1 year (SY) or
years old (ASY) using the appearance
of the number 2 secondary covert feather (Krapu et al. 1979). Radio-transmitters,
weighing approximately 7.0 grams, with a 120 day life expectancy, and operating in
the 151 MHz range (Advanced Telemetry Systems Inc., Isanti, MN) were surgically
attached to captured female mallards using techniques developed by Mauser and Jarvis
(1991). Decoy traps were removed after capture to prevent further disturbance of the
pair.
Monitoring of radio-marked females began 1-2 days following capture.
Mallard females were relocated using truck mounted non-directional whip antennas.
A hand held Yagi antenna was used to approach birds on foot for visual observation to
ascertain status of individual females (i.e. feeding, loafing, and nesting). Monitoring
schedules were randomly assigned for all radio-marked females, and attempts were
made to locate each bird at least 3 times a week between 0700 and 1900 hrs.
Monitoring of individual females was discontinued when the female died, successfully
hatched a nest or left the study area and was not detected for> 14 days (Lokemoen et
al. 1990). Aerial surveys supplemented ground surveys and were conducted at
approximately 2-3 week intervals to relocate females undetected by ground surveys
(Gilmer et al. 1981).
9
Locations of individual females were recorded using Universal Transverse
Mercator (UTM) grid coordinates and plotted on USGS topographic maps and aerial
photographs. In assessing movements of females that either died or lost their
transmitters, I assumed the female transported the transmitter to the recovery location.
HABITAT SAMPLING
Habitat characteristics were measured at sites where radio-equipped and
incidental mallard nests were found (Table 1). Incidental mallard nests were
discovered when unmarked females were flushed from nests during monitoring of
radio-marked females. UTM grid coordinates of all nests were recorded and plotted
on USGS topographic maps and aerial photographs. Wetland types used by females
were plotted on National Wetlands Inventory maps and were classified according to
Cowardin et al. (1979). Nesting cover was classified into 1 of 15 community types
(Kagan and Caicco 1992) (Appendix A).
Upon nest discovery, nest cover characteristics were measured within a 1 m radius
of the nest bowl center (microhabitat) (Table 1). Microhabitat features for each nest
included; 1) the four most dominant plants identified to by species (Hitchcock and
Conquist 1973, Pojar and MacKinnon 1994); 2) percent composition of trees, shrubs,
grasses, forbs and rushes/sedges; 3) cover height estimated by placing a 5 cm diameter
rod, marked at 1 -dm intervals along the edge of the nest bowl; 4) horizontal nest cover
was rated from 0 to 4 (in 0.25 increments) when viewed from a height of 0.3 m, at a
distance of 1 m in the four cardinal compass directions (Hines and Mitchell 1983). A
10
concealment value of 0 was assigned when the nest was plainly visible (i.e. when no
sides of the nest were concealed by vegetation). A concealment value of 4 was
assigned when all sides were hidden from view; 5) Canopy closure was determined by
placing a 25 cm diameter disk on top of the nest bowl and recording the percentage of
the disk obscured by vegetation from a height of 1.5 meters.
Several other site characteristics were quantified, including distance from the
center of the nest bowl to community edge, and nearest water, building, road and trail.
All measurements were recorded using a 100 m tape.
Table 1. Habitat characteristics recorded at mallard nests in the Willamette Valley of
Oregon, 1995-96.
Characteristics
Within 1 Meter of Nest Bowl
Four Dominant Plant Species
Tree Cover
Shrub Cover
Grass Cover
Forb Cover
RushlSedge Cover
Cover Height
Horizontal Cover
Canopy Closure
Vegetative Community
Greater Than 1 Meter from Nest Bowl
Distance to Community Edge
Distance to Nearest Water
Distance to Nearest Trail
Distance to Nearest Road
Distance to Nearest Building
Units
Category
(%)
(%)
(%)
(%)
(%)
(dm)
Numerical
(%)
Category
(m)
(m)
(m)
(m)
(m)
11
REPRODUCTIVE BIOLOGY
Upon discovery of nests, clutch sizes were recorded and eggs were candled
(Weller 1956) to estimate stage of incubation and predict hatching dates. To avoid
unnecessary disturbance, nests were visited only twice; the first time when the nest
was found and the second time when the telemetry data indicated termination of the
nest.
When nest failure was confirmed, the date of failure was estimated as 40% of
the interval (nest-days) since the last observation (Miller and Johnson 1978, Pollock et
al. 1989) if failure date was unknown. I defined a nest as any depression containing 1
or more eggs (Miller and Johnson 1978) and a hatched nest as having hatched
egg
(Klett et al. 1986). Successful nests were distinguished from depredated nests by the
presence of detached shell membranes (Girard 1939, Klett et al. 1986). Eggshells
from depredated nests were collected for later analyses to determine the identity of the
predator species (Rearden 1951, Einarsen 1956).
Nest survival rates were estimated with the Mayfield estimator (Mayfield
1975, Miller and Johnson 1978) using the computer program MICROMORT (Heisey
and Fuller 1985). To identify portions of the nesting period with homogeneous
survival rates, the nesting interval was partitioned into six, 1 week long periods based
on the longest recorded mallard egg-laying and incubation time span (13 eggs with a
26 day incubation period). Nest survival probabilities were tested using likelihood
ratio tests (LRT) for a reduced model where combined weekly intervals provided
adequate fit to the data. Where no difference was detected (p> 0.05) adjacent
12
intervals were combined and a survival estimate for the combined interval was
calculated. The LRT was repeated until all adjacent homogeneous intervals were
combined.
If a female failed to return to a nest after the initial visit, as determined by
telemetry, the abandonment was classed as observer caused and the nest was not used
in the nest survival calculation (Cowardin et al. 1985).
Female survival during the breeding season was estimated using
MICROMORT (Heisey and Fuller 1985, Pollock et al. 1989). Survival was estimated
for each of 17 one-week long intervals based on the period between capture of first
female and departure from study area of last unsuccessful female. For females that
moved out of the study area, lost their transmitters and/or their transmitter failed, their
remaining days of the breeding season were censored from analyses.
Analysis of nest initiation, incubation and hatching time periods was
descriptive in nature and summary statistics were produced for each respective time
period. Female success was determined by dividing the number of successful females
by the number of females attempting at least one nest. Nesting effort was defined as
the number of nests per female.
13
DATA ANALYSIS
Convex polygon (Mohr 1947, Odum and Kuenzler 1955) breeding season
home range sizes were estimated using CALHOME (refer to Larkin and Halkin 1994).
Correlation analyses comparing number of locations (per bird) to polygon size were
used to ascertain effects of sample size on area estimates. Breeding range sizes were
then tested for differences between years using a Wilcoxon Rank-Sums Test (Steel
and Torrie 1980).
Wetland and cover type availability within individual home ranges was
estimated using the grid dot method. Wetland types used by females were classified
according to Cowardin et al. (1979) and vegetative community types were classified
according to Kagan and Caicco (1992). Habitat selection rankings were determined
with the computer program PREFER (Johnson 1980). This method utilizes the
difference between the ranks of usage and ranks of availability as a measure of
selection and is less sensitive to inclusion of habitat components that may not be truly
available to the female.
Vegetative and physical habitat data collected at nest sites was analyzed using
logistic regression (PROC LOGISTIC; SAS Institute Inc. 1987). The response
variable was treated as a binary random variable equal to 1 when a mallard nest
successfully hatched or 0 when a nest failed. The primary goal of this analysis was
addressed retrospectively by looking at: 1) how the probability of predicting nest fate
was dependent upon vegetative and physical habitat characteristics, and 2) how the
probability of predicting nest fate was affected by changes in explanatory variables.
14
The analysis was performed using drop in deviance F-tests to determine variable
combinations that sufficiently answered the questions of interest.
Vegetative and physical characteristics were compared to null models with no
explanatory variables. Each habitat variable that resulted in the largest significant
drop in deviance was included in the final model. The drop in deviance and drop in
degrees of freedom were compared to a chi-square distribution to determine
significance. The additive model was then compared to each remaining variable,
sequentially adding those variables that resulted in a further significant drop in
deviance. A significant drop in deviance (p <0.05) was used as criteria for inclusion
of variables into the final logistic regression models. Whenever a variable was
marginally significant (p 0.05), the Wald Type III test was referenced to determine if
the variable should be included in the final models. The goodness-of-fit of the final
models was assessed with the Hosmer-Lemeshow test (Hosmer and Lemeshow 1989).
15
RESULTS
CAPTURE, MARKING and MONITORING
In the spring of 1995 and 1996, 72 female mallards were captured and
equipped with radio transmitters. I obtained 1,161 telemetry locations upon which the
following analyses are based. Sample size varied among years because of success in
capturing females.
Beginning in mid-March 1995, 32 female and 60 male mallards were captured
and banded at 10 trapping sites. The 32 females fitted with radio transmitters
consisted of 18 second-year (SY) females and 14 after-second-year (ASY) females.
Two females were probably migrants and left the study area within 2 weeks after
capture and 1 radio failed reducing the sample size to 29 marked females.
Beginning in early March 1996, 40 female and 68 male mallards were captured
and banded at 15 trapping sites. Five of the females were previously captured and
monitored in 1995. The 40 females fitted with radio transmitters consisted of 19 SY
females and 21 ASY females. Three females were probably migrants and left the
study area within 1 week after capture reducing the sample size to 37 marked females.
Four additional females had initiated nests prior to capture and were not included in
home range calculations and wetland and nesting habitat preference analyses.
16
Habitat Use and Selection
Analysis of use/availability data by year yielded similar orders of selection for
wetland and nesting habitats, therefore, data for these variables were pooled among
years for analysis.
Home Range Sizes
Sixty-two female mallard breeding home ranges were calculated from sample
sizes ranging from 7 to 38 locations/bird. No relationship was detected between
number of locations/bird and breeding home range area (r = -0.06, p
Breeding home range did not differ for females between years (z
0.64).
-.353, p = 0.72)
and averaged 744 ha (SD=774) (Table 2).
Five females were monitored during both 1995 and 1996 breeding seasons.
All of these females exhibited breeding home range fidelity by returning to locations
within 300 m of locations occupied during the previous breeding season.
Table 2. Home range size of radio-marked pre-nesting female mallards in the
Willamette Valley of Oregon, 1995-1996.
Minimum convex polygon (ha)
Maximum
Minimum
SD
918
7
3494
Year
N
Mean
1995
29
772
1996
33
720
636
Pooled
62
744
774
15
2646
17
Wetland Selection
The hypothesis that wetland habitats were selected in proportion to their
availability within home ranges was rejected for the pre-nesting period (F= 8.00, 7, 55
df, p <0.005) and nesting period (F = 7.20, 7, 32 df, p <0.005).
Eight different wetland types were available within pre-nesting home ranges.
The wetland habitat type most selected by pre-nesting mallard females was permanent
lacustrine, followed by seasonal riverine (Table 3).
The least selected wetland type
was farmed/tilled, followed by temporary palustrine.
During the nesting time period, female mallards used eight wetland types. The
most selected wetland types during the nesting period were seasonal riverine, followed
by permanent lacustrine, permanent riverine and semi-permanent palustrine (Table 3).
The least selected wetland type was farmed/tilled, followed by temporary palustrine.
The most abundant wetland available (57.9 %) in home ranges of females were
seasonal palustrine wetlands, and these wetlands were most frequently used during
both the pre-nesting (73.7 %) and nesting (66.8 %) periods (Table 4). In contrast, the
least available and least used were permanent lacustrine and seasonal riverine, both of
which had high selection ratings (1 & 2, respectively).
18
Table 3. Mean difference among ranks and selection rank of wetland classes used
within home ranges of sixty-two female mallards during pre-nesting and nesting
periods in the Willamette Valley of Oregon, 1995-1996.
Wetland type
Permanent lacustrine
Mean difference among ranks
Pre-nesting
Nesting
-0.62 1
-0.474
Selection rank
Pre-nesting Nesting
Seasonal riverine
-0.476
-0.82 1
2AB
2A
1A
Permanent palustrine
-0.234
-0.192
3BC
5BC
Seasonal palustrine
-0.153
0.256
4C
6C
Semi-perm. palustrine
-0.008
-0.2 18
5CD
Permanent riverine
0.113
-0.4 10
6CD
4ABC
3AB
Temporary palustrine
0.371
0.64 1
7DE
1A
Farmed/tilled
0.992
1.218
8E
a
Habitats with different letter symbols are significantly different (P < 0.05)
b
1 = most selected, 8 = least selected
Table 4. Mean wetland habitat available and use within home ranges of
sixty-two female mallards during pre-nesting and nesting periods in the
Willamette Valley of Oregon, 1995-1996.
Wetland type
Permanent lacustrine
Mean
habitat (%)
Mean use (%)
Pre-nesting Nesting
0.3
1.1
0.1
Seasonal riverine
0.4
0.1
4.3
Permanent palustrine
2.5
3.9
2.4
Seasonal palustrine
57.9
73.7
66.8
Semi-perm. palustrine
4.4
2.7
5.6
Permanent riverine
1.8
1.0
3.7
Temporary palustrine
14.3
10.9
12.0
Farmed/tilled
18.4
6.6
5.1
7CD
8D
19
Nesting Habitat Selection
The hypothesis that community types utilized by nesting females were in
proportion to their availability in home ranges was rejected (F = 8.32, 7, 32 df, p<
0.005).
Eight community types were selected by nesting female mallards. The nesting
habitat most selected by female mallards was urbanlindustrial, followed by
bulrushlcattail marsh, open water, black hawthorn riparian, reed canary wetland and
oak/fir forest (Table 5). The least selected nesting habitats were ash - cottonwood
riparian and agricultural cropland and pasture. These latter two habitats were the most
abundant in home ranges (x=73.6%) and contained 5 8.1% of the nests (Table 6).
Within the eight community types chosen for nesting, forty-one different plant
species were recorded within a one-meter radius around mallard nests (Appendix B).
20
Table 5. Mean difference among ranks and selection rank of nesting habitats
within thirty-nine female mallard home ranges in the Willamette Valley of
Oregon, 1995-96.
Habitat at nest
Mean difference
among ranks
Selection
rank"
Urban/industrial
-0.654
1A
Bulrushlcattail marsh
-0.564
2A
Openwater
-0.527
3A
Black hawthorn riparian
-0.372
4A
Reed canary wetland
-0.295
5A
Oak/ Douglas fir forest
-0.167
6A
Agricultural cropland
1.256
7B
Ash/cottonwood riparian
1.321
8B
a
b
Habitats with different letter symbols are significantly different (P < 0.05)
1 = most selected, 8 = least selected
Table 6. Mean nesting habitat available and use within home ranges of thirty-nine
female mallards in the Willamette Valley of Oregon, 1995-1996.
Mean available
habitat (%)
Mean use (%)
1.1
1.0
Bulrush/cattail marsh
3.4
2.6
Open water
2.5
5.1
Black hawthorn riparian
12.0
17.9
Reed canary wetland
4.8
11.5
Oak/ Douglas fir forest
2.6
3.8
Agricultural cropland
58.2
41.4
Ash/cottonwood riparian
15.4
16.7
Wetland type
Urban/industrial
21
Nest Site Characteristics
Percent tree (x = 6.2%, range 0 - 100%), shrub (x = 12.6%, range 0 - 90%),
grass (x = 67.1%, range 0 100%), forb (x = 10.2%, range 0 100%) and rushlsedge
(x = 3.8%, range 0 - 92%) cover at nests was highly variable. Vegetation height at
nests averaged 10.1 dm, but varied greatly (range 2.2 - 22.5 dm). Mean horizontal
cover value was 3.1 (range 0.5 4) and canopy closure averaged 58.4% (range 0 100%).
Distance to community edge averaged 40.3 m but was highly variable (range
0.3 - 722 m). Distance to nearest water, trail, road and building were all highly
variable and averaged 58.1 m (range 0.1 384.8 m), 38.9 m (range 0.3 252.2 m),
159.6 m (range 2.6-720.1 m) and 350 m (range 25.9-3,025 m), respectively.
REPRODUCTIVE BIOLOGY
Nesting Effort
A total of 60 nests were initiated by 43 radio-marked female mallards during
spring 1995 and 1996. I was unable to locate nests for 23 radio-marked females. In
1995, 16 radio-marked females initiated 0 nests, 12 females initiated 1 nest each, and 1
female initiated 2 nests (x = 0.48 nests/female, SD = 0.57); (Table 7). In 1996, 7
radio-marked females initiated 0 nests, 18 females initiated 1 nest each, 8 females
initiated 2 nests each, and 4 females initiated 3 nests each (x = 1.24 nests/female, SD =
22
0.89). In addition, 26 nests of unmarked females were incidentally located and
monitored; 13 nests each in 1995 and 1996.
Table 7. Nesting effort of radio-marked female mallards in the Willamette Valley
of Oregon, 1995-96.
Number of nests initiated
Nests!
female
Years
0
1
2
3
Total
nests
1995
16
12
1
0
14
0.48
SD
0.57
1996
7
18
8
4
46
1.24
0.89
Pooled
23
30
9
4
60
0.91
0.85
Nesting Chronology
The observed reproductive period for mallards was approximately 3.5 months
(mid-March - late-June) (Fig. 2). The earliest observed nest was initiated on 12
March, and mean nest initiation date was 5 May and 6 May for 1995 and 1996,
respectively. The last recorded nest initiation occurred 25 June. Re-nesting attempts
were initiated from mid-April through the end of June, with the peak occurring around
mid-May (Fig. 2). Hatching of nests occurred from early April through the end of
June, with the peak occurring around the second week of May (Fig. 2). The central
span of nesting (10% to 90% of initiations) as defined by Hammond and Johnson
(1984) was 54 days.
23
20
1St nest 02nd nest 0 3rd nest 0 Hatching
15
10
0
Mar. 16-31
Apr. I-IS
Apr. 16 3(
May 1-15
May 16-3 I
JI.n. I-IS
Jun 16-30
Initiation and Hatching Date
Figure 2. Nest initiation and hatching chronology of radio-marked female mallard
nests (n=85) in the Willamette Valley of Oregon, 1995-96.
24
Nest Survival
In 1995 and 1996, 23 of the 86 nesting attempts successfully hatched young
(determined by presence of hatched eggs in nests and/or observations of young). One
nest was abandoned due to observer presence and was deleted from analyses (Table
One hundred forty nine ducklings were hatched in 17 nests of marked females, and
59 ducklings were hatched from 6 nests of unmarked females. Average size of broods
at hatching was 9.0 young. Destruction of nests by predators accounted for 84% of
nest failures, with abandonment and other mortality sources (i.e. weather and
agricultural equipment) each accounting for 8% of nest failures.
Overall nest survival was best represented when the 6-week nesting cycle was
divided into two periods. Based on the Likelihood Ratio Test (LRT), the early period
had an interval length of 14 days, approximately the length of the laying period (Table
Daily nest survival rate during the laying and incubation periods was 0.977 (SE =
0.005) and 0.954 (SE = 0.007), respectively. Overall nesting cycle survival
probabilities varied from 0.106 in 1995 to 0.216 in 1996, with a pooled nest survival
rate of 0.186 (SE = 0.043).
Lowest success occurred in reed canary wetlands (14.3%, n
21) and the
highest occurred in bulrush-cattail marsh (33.3%, n = 3) and open/over water (33.3%,
n = 3); (Fig. 3). The single nest in oak-fir forest failed while the single nest in
urban/industrial succeeded.
25
Table 8. Fate of 86 mallard nests in the Willamette Valley of Oregon, 1995-96.
Year
All Years
Total
% of Total
23
26.7
1995
6
1996
Mammalian predator
16
35
51
59.3
Agr. equip. abandoned
2
2
4
4.7
Flooding
0
3
3
3.5
Avian predator
1
1
2
2.3
Agr. equip. destruction
0
2
2
2.3
Observer abandoned
1
0
1
1.2
Unsuccessful total
20
43
63
73.3
Grand total
26
60
86
100
Successful total
17
Unsuccessful categories
Table 9. Mayfield survival rates of radio-marked and incidental mallard nests in the Willamette Valley of Oregon, 1995-96.
Daily survival
Period 1
Year
1995a
1996b
Pooleda
a
N
26
Exposure
days
327
59
85
Period 2
A
0.979
SE
0.008
Exposure
days
208
738
0.976
0.006
1065
0.977
0.005
S
Nesting cycle
A
0.938
SE
0.017
Survival
probability
0.106
594
0.96
0.008
0.216
0.056
0.137-0.364
802
0.954
0.007
0.186
0.043
0. 122-0.298
S
Period 1 (weeks 1-2 combined); Period 2 (weeks 3-6 combined)
bpid
1 (weeks 1-3 combined); Period 2 (weeks 4-6 combined)
95%
SE Confidence limits
0.062
0.044-0.332
27
30 -
25 -
20 -
15 -
10 -
5-
0
0
0
o
oo
0(n
Community Type
0 successful
J unsuccessful
Figure 3. Number of successful and unsuccessful mallard nests (n85) by plant
community type (Kagan and Caicco 1992) in the Willamette Valley of Oregon, 199596.
28
Female Success
Sufficient information was available for 43 nesting female mallards to
calculate female success (13 in 1995 and 30 in 1996) (Table 10). Overall female
success was 39.5% with 52.1% of ASY females successful and 25.0% of SY females
successful for both years combined. In 1995, overall female success was 23.1%, and
was 0% and 50.0% for SY and ASY females, respectively. In 1996, overall female
success was 46.7%, and was 3 8.5% and 52.9% for SY and ASY females, respectively.
Table 10. Percent of radio-marked female mallards with a successful nest in one of
their attempts in the Willamette Valley of Oregon, 1995-96.
n % success
All years
1996
1995
n
% success
% success
25.0
Secondyear(SY)
7
0.0
13
38.5
n
20
After second year (ASY)
6
50.0
17
52.9
23
52.1
All ages
13
23.1
30
46.7
43
39.5
Age of female
Female Survival
Seventy-two radio-marked mallard females were used to calculate breeding
season (March-June) survival estimates. In 1995 and 1996, female survival data were
represented most parsimoniously when divided into two periods, weeks 1-4 and 5-11,
and weeks 1-6 and 7-17, respectively. Based on the LRT, female survival data for
both years were pooled across all survival periods (pre-laying, laying and incubating)
29
into a single 17-week interval (p> 0.05). Adult survival probability for combined
breeding seasons of 1995 and 1996 was 0.668 (SE = 0.078) (Table 11).
Table 11. Daily and breeding season (March-June) survival rates of radio-marked female mallards in the Willamette
Valley of Oregon, 1995-96.
Period 1
A
Year
# Female
days
1995a
1262
199&'
2308
Pooledc
3570
a
Daily survival
Period 2
A
S
Survival
Probability
Nesting season survival
95%
SE
Confidence limits
0.106
0.325-0.855
0.996
SE
<0.001
0.989
SE
<0.001
0.999
<0.001
0.996
<0.001
0.733
0.093
0.544-1.000
0.997
<0.001
0.997
<0.001
Period 1 (weeks 1-4 combined); Period 2 (weeks 5-1 icombined)
0.668
0.078
0.537-0.842
S
bPeiod 1 (weeks 1-6 combined); Period 2 (weeks 7-l7combined)
cNo separate periods (all weeks combined)
0.511
31
There were 12 confirmed female mortalities (8 in 1995, 4 in 1996), of which 4
were killed on nests (2 in both 1995 and 1996). At mortality sites, remains of females
ranged from a transmitter and a few wing feathers to completely intact remains
(farming related mortality). In most cases, I was unable to positively ascertain cause
of death. Therefore, mortalities were classified as either mammalian predator, avian
predator, farming related, or unknown predator. The species responsible for predation
on females was difficult to determine from the characteristics and thus was somewhat
subjective. In several instances predators were flushed from recently killed radiomarked females or predator tracks were present at the site.
In 1995 and 1996, the breakdown of predation on radio-marked females was
unknown predator 42% (n=5), mammalian predator 33% (n=4), avian predator 17%
(n=2), and farming related 8% (n=1).
32
NEST SUCCESS-HABITAT RELATIONSHIPS
Only one of the fifteen vegetation and physical habitat characteristics were
found to differ (p < 0.05 from drop-in-deviance F-test) between successful and
unsuccessful mallard nests (Table 12). Logistic regression indicated that horizontal
cover was a significant predictor of nest fate (W = 3.86, p = 0.049). Log odds ratios
showed mallard nests were 1.95 times more likely to succeed with every one-unit
increase in horizontal cover. Fit of predicted probability of nest success was adequate
(p
0.149 from Hosmer and Lemeshow Goodness-of-Fit test) using nest success as
the response variable and horizontal cover as an explanatory variable (Table 13).
33
Table 12. Drop-in deviance F-test for vegetation and physical habitat
characteristics of successful mallard nests in the Willamette Valley of Oregon,
1995-96.
Model
Null model
Degrees of Freedom
Full
Drop-in
Drop-in Reduced
model
df
Deviance deviance model
99.25
84
P>F
Horizontal cover
94.50
4.75
84
83
1
0.044
Grass cover (%)
91.88
2.62
83
82
1
0.130
Canopy closure (%)
91.92
2.59
83
82
1
0.132
Forb cover (%)
92.23
2.27
83
82
1
0.159
Vegetation height
92.61
1.90
83
82
1
0.198
Distance to nearest road
92.69
1.18
83
82
1
0.310
Age of female
91.86
2.64
83
81
2
0.317
Nest initiation date
93.44
1.07
83
82
1
0.335
Rush/sedge cover (%)
93.71
0.79
83
82
1
0.408
Distance to nearest building
93.97
0.54
83
82
1
0.494
Distancetonearestwater
94.31
0.19
83
82
1
0.686
Treecover(%)
94.35
0.15
83
82
1
0.719
Distance to community edge
94.48
0.02
83
82
1
0.896
Distance to nearest trail
94.48
0.02
83
82
1
0.896
Shrubcover(%)
94.50
0.01
83
82
1
0.925
34
Table 13. Final logistic regression model for vegetation and physical habitat
characteristics of successful mallard nests in the Willamette Valley of Oregon,
1995-96. Hosmer and Lemeshow Goodness-of-Fit Statistic = 9.466 with 6 d.f.
(p=O. 149).
Model
Parameter
Intercept
Horizontal cover
Change in
coefficient SE odds ratio
-3.156
1.171
0.670
0.341
1.954
95%
P>F
Confidence limits
0.044
1.064-4.126
35
Logit (Y) = -3.156 + 0.670 (horizontal value)
0.4
Predicted Success
- -. -
Observed Success
0.3
00
r)
\r'
vr7
()
Horizontal Cover Value
Figure 4. Predicted probability and observed nest success by mallards in the
Willamette Valley of Oregon, 1995-96, as a function of horizontal cover values (0 - 4).
Hosmer and Lemeshow Goodness-of-Fit Statistic = 9.446 with 6 d.f.; p = 0.149.
36
DISCUSSION
HABITAT SELECTION
Home Range Sizes
Average home range size of breeding female mallards monitored
during this study (743 ha) was larger than those reported for other mallards. Female
mallard home range size averaged 203 - 468 ha in the PPR (Dzubin 1955, Titman
1973, Dwyer et al. 1979) and 210 (Gilmer et al. 1975) and 540 ha in forested north
central Minnesota (Kirby et al. 1985). In Maine, Ringelman et al. (1982) reported
home range size for closely related black ducks (Anas rubripes) averaged 119 ha.
stablished home range sizes for other dabbling ducks have been reported from about
500 ha for northern pintails (Anas acuta); (Derrickson 1975) to under 100 ha for bluewinged teal (Anas discors); (Drewein and Springer 1969), gadwall (Anas strepera);
(Gates 1962) and northern shoveler (Anas clypeata); (Poston 1974).
Differences in home range size among waterfowl species have been attributed
primarily to variations in either density of breeding pairs or quality and distribution of
habitat components (McKinney 1973).
High pair densities lead to increased aggression among pairs (Dzubin 1955)
and is believed to result in reduction of home range size (Gates 1962). In the
Willamette Valley, breeding pair density of mallards is low (2 pairs/km2) compared to
other study areas (5-15 pairs/km2). Although aggression between breeding pairs was
37
observed, the level of this interaction was not quantified and the impact that it may
have on home range size remains unknown.
In the Willamette Valley, the instability of water levels in highly abundant
farmed/tilled, temporary and seasonal ponds and the linear arrangements of many
semi-permanent and permanent wetlands may be the primary factors influencing the
size of mallard home ranges. Home ranges of breeding black ducks (Ringelman et al.
1982) and mallards (Gilmer et al.
1975,
Dwyer et al.
1979)
have shown to be linear.
The linear shape of waterfowl home ranges may reflect use of wetland complexes
linked by streams or within a common drainage (Ringelman et al. 1982).
Although the Willamette Valley receives ample rainfall during winter and
early-spring, most of the farmed/tilled and temporary wetlands on the study area
remained ponded only for a very short period of time (<
1-2
weeks) and most
remained dry from late-April through the end of the nesting season. The rapid drying
of these wetland types was also facilitated by the use of drainage structures (i.e.
drainage tiles) installed in many agricultural fields during the last several decades
throughout the Willamette Valley. During these periods of rapid drying of
farmed/tilled and temporary wetlands, use of seasonal, semi-permanent and permanent
emergent wetlands greatly increased.
A wider range of home range sizes than previously documented suggests a
continuum in response of mallards to the set of wetland habitat conditions available of
varying quality and distribution (Nudds and Ankeny
1982).
Mallard females in the
Willamette Valley used larger home ranges than their counterparts in the prairies.
38
These larger home ranges may have been a result of wetland availability on the study
area. The rapid drying of farmed/tilled, temporary and seasonal wetlands may have
forced some females to utilize a diversity of wetland types to meet the nutritional
requirements needed for nesting. Dwyer et al. (1979) suggested a large home range
containing a diversity of wetland types increases potential options for waterfowl to
meet breeding requirements, and thus would be beneficial under conditions of rapidly
changing and highly unpredictable water conditions typical of prairie wetlands.
Wetland Selection
Results from this study indicate that wetland habitat selection occurred at the
third order (within home ranges); (Johnson 1980). Females were selecting home
ranges that contained a high proportion of seasonal riverine or lacustrine wetland
habitats.
During pre-nesting, permanent lacustrine and seasonal riverine habitats were
selected over palustrine and farmed/tilled wetland habitats. This finding is contrary to
previous studies where female mallards selected seasonal palustrine wetland habitats
over more permanent wetlands (Swanson et al 1985). Seasonally flooded habitats are
known to support higher populations of aquatic invertebrates than more permanently
flooded habitats (Swanson and Meyer 1973) and have been shown to be an important
food source for females and broods (Chura 1961, McNight 1969, Sugden 1973, Talent
et al. 1982, Swanson et al. 1985).
39
Although permanent lacustrine and seasonal riverine wetland habitats had a
higher selection ranking, these two wetland habitats only accounted for 1.1% of the
total wetland use during the pre-nesting period by mallard females. The three top
wetlands according to percentage of use were seasonal palustrine (73.7%), temporary
palustrine (10.2%) and farmed/tilled (6.2%). However, due to their abundance, these
three wetlands ranked 4th, 7th and 8th respectively, in terms of relative selection.
Because a higher selection ranking is usually indicated for items (i.e. wetland habitats)
that are not very abundant, very abundant items will generally have low selection
rankings (Noyes and Jarvis 1985). Therefore, seasonal and temporary palustrine
habitats were highly utilized by female mallards in the Willamette Valley, however,
their abundance within the home ranges of females affected their selection status.
During the nesting period, seasonal riverine, permanent lacustrine, permanent
riverine and semi-permanent palustrine habitats were selected over temporary and
seasonal palustrine and farmed/tilled wetland habitats. However, the four most
selected wetland types accounted for only 14.1% of total wetland use. The three top
wetlands according to use were seasonal palustrine (71 .1%), temporary palustrine
(7.4%) and permanent palustrine (5.6%). These wetlands ranked 6th 7th and 4'
respectively, in terms of relative selection. As was observed during the pre-nesting
period, seasonal palustrine habitats were highly utilized. However, due to their
abundance their selection ranking was low in relation to more permanent wetland
habitats.
40
As previously mentioned, farmed/tilled and temporary wetlands remained
ponded for only a very short period of time. Determination of wetland types available
to females was made shortly after tracking of females was completed. National
wetland inventory maps and aerial photographs were used to identify wetlands within
individual home ranges, however, the time different wetland classes were available to
breeding females was not estimated. As a result, I may have overestimated the
availability of farmed/tilled, temporary, and seasonal wetland types. If overestimated,
this would cause an underestimate of selection of farmed/tilled, temporary, and
seasonal wetlands.
To better assess wetland use and selection by breeding females, the duration of
wetland types available to breeding female mallards needs to be determined. In the
Willamette Valley, temporary and seasonal wetlands remained ponded for short
periods of time, therefore, they are not available throughout the entire breeding season
in comparison to semi-permanent and permanent wetlands. Determining the average
duration of wetland types and how precipitation affects duration is important to better
understanding how these wetlands affect mallard nesting ecology in the Willamette
Valley.
Additional factors that may account for the selection of more permanent
wetland habitats is the isolation these habitats may provide to pairs and their location
in relation to suitable nesting cover. As previously noted, rapid drying of farmed/tilled
and temporary wetlands may have caused radio-marked female mallards to interact
more with other mallard pairs on remaining wetland habitats on the study area. This
41
interaction may have forced some radio-marked females to utilize wetland habitats
that otherwise may have not been selected. These wetlands may be less than ideal for
mallards seeking high quality foods, but they may offer a feeding and loafing place
where they are not pursued by conspecifics (Dzubin 1969). This relationship was
demonstrated by Evans and Black (1956) where they concluded the desire for isolation
by breeding pairs in Waubay, South Dakota led to dispersal of the population and to
intensive use of parts of habitat which would not otherwise have been used. The
relationship of wetland selection to adjacent nesting cover was not analyzed during
this study. However, Drewien and Springer (1969) and Kirsch (1969) have shown
conditions of upland habitat can affect the density of breeding duck pairs in adjacent
wetlands (Fleskes and Klaas 1991).
Nesting Habitat Selection
Results from this study indicate that nesting habitat selection occurred at the
third order (Johnson 1980). Females were selecting home ranges containing high
proportions of urbanlindustrial, bulrushlcattail wetland, open-water, black hawthorn,
reed-canary wetland and fir/oak forest nesting habitats. However, these nesting
habitats accounted for only 29.7% of nesting habitat use. The two top nesting habitats
according to use were agricultural cropland (53.5%) and ash - cottonwood riparian
(16.8%)
In general, uncultivated upland and wetland habitats with a strong cover
component were selected over agricultural cropland and ash-cottonwood riparian
42
habitats. This finding agrees with other studies where undisturbed uncultivated upland
and wetland habitats were selected over croplands (Cowardin et al. 1985, Greenwood
et al. 1995). In central North Dakota, Duebbert et al. (1986) reported that 42% of
mallard nests were in upland habitats dominated by western snowberry
(Symphoricarpos occidentalis) yet this habitat type comprised only 2% of the
available cover. In southeastern Alberta, mallards selected wetlands dominated by
rush communities (Juncus spp.) for nesting cover. Likewise, 66% of the mallards
nesting in the Missouri Coteau of southcentral North Dakota selected wetland sites in
stands of dense emergent vegetation (Krapu et al. 1979).
In contrast, some studies have reported that in agricultural areas, hayfields are
often selected by nesting mallards (Labisky 1957, Milonski 1958, Sayler 1962, Moyle
et al. 1964, Gates 1965, Duebbert 1969, Belirose 1976). However, in many cases
residual cover in hayfields was the only nesting habitat available to early nesting
mallards on the prairies. Later nesting and re-nesting mallards switched to upland
habitats as the vegetative component of these areas increased during the spring.
Unlike most agricultural crop lands throughout the breeding range of the
mallard, the residual cover available to mallards nesting in the Willamette Valley is
sparse. The vast majority of the agricultural cropland is comprised of grass seed
varieties (Lolium sp. and Festuca sp.) that provide little residual cover for early
nesting females. Measurements taken in both annual and perennial grass fields
indicated residual cover of <2 dm in height from early-March through mid-April
when a majority of nests were initiated. As the nesting season progressed, late-nesting
43
and re-nesting mallard females began to utilize agricultural grass fields to a greater
degree. It is likely that this greater use was a result of increased vegetative cover.
Although these croplands provided large, dense blocks of nesting cover later in the
nesting season, most grass seed fields on the study area were disturbed by agricultural
operations. Herbicide spraying (ground and aerial), fertilizing and harvest activities
were observed on most agricultural croplands during the latter half of the nesting
season and were directly responsible for the destruction of 6 nests (4 were abandoned
and 2 were crushed) and the mortality of one radio-marked female.
Uncultivated upland and wetland habitats in the Willamette Valley provided
the bulk of nesting habitat available to early nesting mallards. These habitats are
relatively undisturbed from human activities (except for the urban and industrial
habitat type) and provided the necessary cover needed by early nesting mallards.
Agricultural croplands although large in size, provided nesting cover only during the
latter half of the nesting season and were subject to a high level of disturbance. The
level of disturbance varied from one area to the next and was highly dependent on
crop type and level of inputs (i.e. herbicides and fertilizers) an individual farmer
deemed appropriate.
Nest Site Characteristics
Mallards are widely considered habitat generalists, nesting in a variety of
habitat conditions including forest interiors, grasslands and wetlands, to urban areas.
On the prairies, grasslands (Smith and Stoudt 1968), western snowberry (Cowardin et
44
al. 1985), Juncus communities (Keith 1961) and Whitetop (Cardaria spp.) have been
documented as preferred nesting cover types. In agricultural areas, hayfields are often
preferred in North Dakota (Sayler 1962), Mirmesota (Moyle et al. 1964), Wisconsin
(Labisky 1957, Gates 1965), and Manitoba (Milonski 1958). In the Intermountain
marshes of the west, hardstem bulrushes (Scirpus lacustris) were preferred over other
wetland plants (Wingfield 1951, Hunt and Naylor 1955, Bellrose 1976) and in
Vermont, mallards nested among fallen logs, in hollow tree trunks, and tree crotches
(Coulter and Miller 1968). Mallards also readily accept artificial nest structures of
various forms. In this study, mallard females selected a diversity of nesting habitats
which was evident from the variety of vegetative species found around mallard nests.
Grasses were the predominant (67%) vegetative class found at nest sites, followed by
shrubs (12.6%) and forbs (10.2%), accounted for 90% of the vegetative classes at
mallard nests in the Willamette Valley.
Cover height, canopy closure, horizontal cover and distance to water and
disturbance factors (i.e. buildings, roads and trails) have varied greatly with different
nesting mallards. Livezey (1981) reported an average vegetation height at nests of 46
cm and Bellrose (1976) concluded that a primary requirement of mallard nesting sites
appears to be dense vegetation about 60 cm in height. In this study, mallards selected
sites with an average vegetation height of approximately 100 cm. Canopy closure at
mallard nest sites in the Willamette Valley was highly variable and was partly
influenced by date of nest initiation. Early nests (prior to the May 5 peak initiation
45
date) tended to have less overhead cover than late nests which was likely a result of
increased plant growth during spring.
Mean distance to water was shorter in this study (58.1 m) than reported for
Horicon NWR in Wisconsin by Livezey (1981) and in North Dakota by Cowardin et
al. (1985), and may be a reflection of breeding density of mallards in the Willamette
Valley. Dzubin and Gollop (1972) reported that the more dense the breeding
population, the greater the distance that mallards nested from prairie ponds.
Mean distance to roads, trails and buildings has been documented in few
mallard nesting ecology studies. In North Dakota, Cowardin et al. (1985) reported a
mean distance to travel lanes (roads and trails) of approximately 60 m and a mean
distance to buildings of approximately 1,026 m for both unsuccessful and successful
nests. The mean distance to roads, trails and buildings in this study was 39 m, 159 m
and 350 m, respectively. This large difference is likely a result of different land use
patterns between the PPR and the Willamette Valley. The Willamette Valley is home
to over 2 million people scattered throughout many portions of the valley. This
settlement pattern, unlike the prairies of north central U.S. creates a mosaic of
agricultural lands interspersed with industrial areas, homes, and farm buildings. Large
continuous tracts of nesting habitat (outside of refuges and wildlife areas) are
uncommon and proximity of duck nests near man-made structures (buildings and
roads) is greater in the Willamette Valley.
46
REPRODUCTIVE BIOLOGY
Nesting Effort
In this study a high proportion (3 4.8%) of radio-marked females did not initiate
nests. However, nesting propensity may have been underestimated. Failure to detect
nesting by females mallards has been previously documented and may occur because
of 1) the difficulty of locating nests of some females during the laying period because
they spend a short time at the nest, 2) these nests may have been destroyed before
being discovered (Cowardin et al. 1985), 3) some females are killed prior to initiating
nests, 4) they are highly mobile, traveling beyond the study area, and 5) some mallards
probably do not nest in their first year (Johnson et al. 1992).
The probability of finding nests that fail during egg laying is low (Cowardin et
al. 1985). During the laying period, females spend little time (< 1 hour) at the nest site
and it is during this period in which investigators can fail to document nest attempts.
Nesting attempts near the margins of wetlands could have been mistaken as feeding or
loafing activities by observers. Every attempt was made to acquire a visual
observation of all females without undue harassment. However, the location of some
females was determined by triangulation of radio signals and not direct observations.
Some females during this study (3 SY and 9 ASY) were killed during the peak
month of breeding (April), further reducing our potential to verify all nesting attempts.
Lokemoen et al. (1990) found proportionately fewer nests of SY females (36%)
compared with older females (63%) and suspected that a segment of the population
47
contained nonbreeding females. Caverley and Boag (1977) examined the reproductive
tracts of mallards (ages pooled) and reported non-breeding rates of 5% in Alberta and
17% in Northwest Territories. Nevertheless, the percentage of non-breeding females
in a population is difficult to estimate considering that non-breeding females
sometimes are physiologically capable of breeding (Johnson et al. 1992). Factors that
could cause a significant reduction in nesting rates include climatic conditions or
availability of food resources (Krapu et al. 1983). In 1996, localized flooding caused
abandonment of three mallard nests and may have delayed nest initiation in other
females. In addition, resource competition among mallard pairs during drawdown
periods of wetlands may have caused some females to forgo nesting due to the lack of
acquisition of necessary food resources critical to egg development and egg viability.
Nesting Chronology
Mallards exhibit a long and varied breeding season in relation to other duck
species. They nest early and are persistent re-nesters (Klett et al. 1988). Mallard
breeding seasons range from 30 days in the Northwest Territories, 75 days in central
Washington (Bellrose 1976) and New York (Losito et al. 1995), to 104 days in west
central Saskatchewan (Gollop and Fyfe 1956). The mallard begins nesting between
April 10 and April 30 over vast reaches of its breeding range, with the peak of nest
initiation occurring between May 5 and May 20 (Bellrose 1976).
During this study, the breeding season persisted for 3.5 months, starting in
late-March and continuing through late-June, with the peak of nesting occurring
48
around May 5. The 107 day period between the first and last nest initiations is one of
the longest to be documented for wild mallards. The central span of nesting (10% to
90% of initiations) was 54 days and compares to a span of 48 days reported by LosiLto
et al. (1995) in New York and 47 days reported by Hammond and Johnson (1984) in
North Dakota.
Vaisanen (1974) suggested that laying dates are partly fixed by heredity and
are modified by environmental conditions and age of the bird. The correlation
between heredity and laying date has been supported by Perrins (1970), Spurr and
Milne (1976) and Batt and Prince (1979) and the importance of age of nesting females
on initiation of egg laying has been suggested by Coulter and Miller (1968) and Krapu
and Doty (1979). In this study I found no significant relationship between age of
female and nest initiation date, however, ASY females initiated 5 of the 6 earliest
nests and SY females initiated 5 of the 6 latest nests.
Environmental conditions including photoperiod (Marshall 1961, Raveling
1978), access to nesting and feeding sites (Marshall 1961, Perrins 1970, Krapu and
Doty 1979), and weather, may have direct effects on birds and indirect effects through
changes in nesting habitat and food resources (Marshall 1961, Vaisanen 1974,
Raveling 1978, Krapu and Doty 1979, Hammond and Johnson 1984). Water
conditions are known to influence mallard nesting activity through their effect on
abundance of food resources sought by females preparing to nest. Seasonal wetlands
in the PPR are a major foraging habitat of mallards (Dwyer et al. 1979) and
availability of food declines sharply during periods of drought or drawdown. Food
49
quality and abundance influence both egg production and egg viability (Krapu 1979).
When high quality food is abundant, females are capable of producing several
clutches. Under conditions of low food availability, however, the incidence of renesting decreases (Krapu et al. 1983).
Duration of nesting activity is strongly influenced by water conditions because
re-nesting females need abundant food sources. As habitat deteriorates because of
drought or drawdown, aggression intensifies, forcing an increasing number of pairs
into sub-optimal habitat or emigration and the probable abandonment of nesting for
the year. In this study, aggression between mallard pairs was observed throughout the
nesting season. Although not quantified, this interaction may have forced some
females into sub-optimal habitats where the level of food resources may have been
inadequate to initiate nests. To compensate for inadequate food resources females
may have been forced to either forgo nesting for the year, try to compete with other
females at more optimal feeding sites, or delay nesting until more optimal sites
became available.
The level of interaction among pairs can be expected to vary widely among
years, primarily because of the instability of water conditions and, ultimately, the food
supply (Krapu et al. 1983). In South Dakota, Evans and Black (1956) considered that
a rapid drop in water levels retarded late season nesting and that a long nesting season
occurred only when water conditions were favorable.
The date when nest initiation begins and duration of nesting effort are
important for waterfowl because female success is a function of nest success and re-
50
nesting rate (Cowardin et al. 1985). Reasons for a long breeding season in the
Willamette Valley are not fully understood. Climate of the Willamette Valley seems
to provide relatively abundant wetland resources from year to year, thus giving
mallards a consistently timed and long breeding season. However, overall level of
nesting effort by females was lower than other studies, indicating a potential problem
may exist in the acquisition of resources for pre-laying females. Further comparison
of environmental conditions (i.e. wetland availability and food abundance) in relation
to nesting effort may provide additional insight into mallard nesting requirements in
the Willamette Valley.
Nest Survival
The average nest survival estimate of 19% (95% C.I. = 0.122 - 0.298) in the
Wiliamette Valley was higher than estimates of 8-11% in North Dakota (Cowardin et
al. 1985, Lokemoen et al. 1990), 9% in north-central Iowa (Fleskes and Klaas 1991),
and was comparable to the 18% reported for the St. Lawrence River Valley, New
York (Losito et al. 1995) and central South Dakota (Klett et al. 1988).
Like most studies of nesting ducks (Greenwood et al. 1987, Johnson et al.
1987, Klett et al. 1988), predation was the primary cause of nest loss in this study
accounting for 84% of all nest losses. Although no formal predator surveys were
conducted in this study, observations of predator activities were noted and anecdotal
information concerning predator occurrence were provided by landowners.
51
Variation in nest success results from variation in predator communities whose
numbers, species composition, and food preferences vary in space and time (Cowardin
et al. 1985). The higher nest survival rate (this study) than reported from the prairies
may be due to differences in composition and abundance of predators. Predators of
prairie duck nests which are also found in the Willamette Valley include red fox
(Vulpes vulpes), raccoon (Procyon lotor), striped skunk (Mephitis mephitis), opossum
(Dideiphis virginiana), coyote (Canis latrans) and American crow (Corvus
brachyrhynchos). The effect that each species has on the survival rate of ducks nests
varies between studies. However, in most cases the red fox was identified as the
principal predator of duck nests (Johnson et al. 1988)
Although red fox are considered an important predator of duck nests in the
prairies none were observed on the study area, however, coyotes were occasionally
observed. Johnson et al. (1989) detected a strong negative relation between red fox
and coyote activity indices, consistent with the spatial avoidance and antagonistic
behavior between these two species. A similar avoidance distribution may have also
influenced the distribution of coyotes and raccoons (Johnson et al. 1989) and redtailed hawks and American crows (Sargeant et al. 1993) on my study area.
Red fox tend to occupy smaller home ranges, have higher reproductive rates
and breed during their first year, unlike the coyote (Johnson and Sargeant 1977).
Each fox must draw its food from within its territory (Sargeant 1978) and is able to
scent and locate nesting duck females at distances as great as 30 m (Fleskes and Klaas
1991). Sovada et al. (1995) found in areas of similar habitat, nest success of dabbling
52
ducks averaged 15% higher in areas occupied by coyotes than in areas occupied by red
foxes.
The red fox is a highly skilled predator of duck nests in the prairies and has
been identified by a number of studies as the primary predator of dabbling duck nests.
On my study area, the red fox was largely replaced by the coyote, which tend to be
much less effective at discovering duck nests. Although the extent to which individual
predator species impact duck nests in the Willamette Valley is unknown, further
analysis is warranted. Predator control programs to increase duck production have
been shown to be effective in the prairies. However, a nest survival rate of 19% is
above the 15% identified as needed to sustain a local mallard population. Therefore, a
predator control program may be urmecessary unless mallard nest survival rates drop
below 15%.
Female Success
Female success rates for mallards have been documented from 9% in
Sakatchewan (Devries et al. Unpubl data) to 57% in Manitoba (Dzubin and Gollop
1972). A higher female success rate of 88% was reported by Cowardin and Johnson
(1979) in North Dakota, however, this high rate was a result of an extensive predator
control effort on one study area. Female success rates for two other study areas were
29% and 39%, respectively (Cowardin and Johnson 1979). In this study, overall
success of females who attempted at least one nest was 40.5% and is comparable to
53
the 40 - 49% success rate reported for mallards in other portions of their range (Keith
1961, Smith 1971, Stoudt 1971, Gollop 1972).
In 1995, female success was highly variable (0% for SY females and 60% for
ASY females), however, we were only able to document nesting attempts by 13
females which makes comparison of female success rate among years difficult. Lack
of success by SY females was also documented by Cowardin et al. (1985) during one
year of a four year study in North Dakota. In 1996, we were able to calculate success
rate based on 30 females and a significant increase in the SY female success rate was
observed. The dramatic difference between years is likely a result of increased sample
size of SY females and to a lesser degree, increased vigilance among field observers to
document daily female activities (i.e. nesting attempts). During 1995 and 1996, ASY
female success rates were 60% and 53%, respectively. This higher success rate for
ASY females versus SY females has been documented by others (Cowardin et al.
1985, Losito et al. 1995) and is likely a result of either increased nesting effort, more
ASY females attempting nests, or nesting experience by ASY females.
Female success is probably the most important measure for evaluating
recruitment because it is a function of both nest success and re-nesting rate (Cowardin
et al. 1985). In the Willamette Valley, female success for mallards is higher than
reported for much of the Prairie Pothole Region. I suggest this is largely a result of a
greater nest success rate combined with a lower nesting effort rate. In the Willamette
Valley, nest success by mallard females during this study was 19%, higher than the
8% - 11% reported for the prairies. With a higher nest survival rate, females in the
54
Willamette Valley have to attempt fewer nests in order to be successful, thus,
achieving a higher female success rate.
Female Survival
I assumed transmitters on females would have little effect on behavior or
survival probabilities. Evidence collected concerning female survival indicated little
or no impact and unusual female behavior (i.e. excessive preening around transmitter
or erratic flight) was not observed. This is in agreement with other studies concluding
that suture mounted transmitters had a negligible impact on mallard females (Houston
and Greenwood 1993, Rotella et al. 1993). In addition, marking of females during the
pre-nesting period allowed some females up to 3 weeks acclimation to transmitters
prior to nest initiation and incubation of clutches.
Overall breeding season survival rate obtained in this study in 1995 (0.668)
and 1996 (0.734) is comparable to the 0.600 - 0.800 survival rates reported for the
prairies (Sargeant and Raveling 1992). A higher survival rate of 0.789 during the
incubation period was reported by Kirby and Cowardin (1986) in north central
Minnesota and Mauser and Jarvis (1994) reported a high survival rate (0.830) among
radio-marked females in northern California.
In most studies, mammalian predators appear to kill more female mallards than
do any other source during the breeding season (Keith 1960, Stout and Cornwell 1976,
Johnson and Sargeant 1977, Cowardin et al. 1985), although avian predators may have
considerable impact in certain areas. Species implicated in significant predation on
55
adult ducks on the prairies include red fox, mink (Mustela vison), and long-tailed
weasel (Mustelafrenata) (Kalmbach 1937, Keith 1961, Sargeant 1972, Eberhardt and
Sargeant 1977, Johnson and Sargeant 1977).
On my study area red fox were uncommon, likely a result of the abundant
coyote population. Coyotes, unlike red fox are not considered an efficient predator of
adult ducks (Sargeant et al. 1993). Long-tailed weasels were not observed on the
study area and are considered uncommon on the valley floor (Larry Cooper personal
comm.) and mink are common, although none were observed during this study.
The Willamette Valley is home to a suite of predators capable of taking nesting
ducks. Impacts individual predator species have on nesting ducks in the Willamette
Valley is largely unknown and research into predator-nesting duck dynamics would be
beneficial to better understand mallard breeding season survival rates.
Cowardin et al. (1985) concluded that females have a greater risk of predation
while on the nest than off the nest. However, in this study, no significant difference in
survival rates were detected between prelaying, laying and incubating females. The
breeding season survival estimate from this study (0.668, 95% CI = 0.537 - 0.842)
indicates that the breeding season (March - June) is a period of high adult mortality
and is likely a maj or factor affecting mallard recruitment in the Willamette Valley.
56
NEST SUCCESS - HABITAT RELATIONSHIPS
Microhabitat evaluations of nest site concealment, canopy coverage and related
physical attributes have fostered conflicting views on the importance of structural
features of vegetation to duck nesting success (Gilbert at al. 1996). I found nesting
success improved with increasing horizontal cover provided by vegetation near nest
sites. This contrasts with results of many earlier studies that did not show much
difference in vegetation at successful and unsuccessful nests (Kalmbach 1937, 1938,
Furniss 1938, Hammond 1940, Glover 1956, Steele et al. 1956, Milonski 1958,
Dwernychuk and Boag 1972, Byers 1974). But it is in agreement with other
investigations (Odin 1957, Choate 1967, Chesness et al. 1968, Enright 1971, Bengston
1972, Schrank 1972, Livezey 1981, Hines and Mitchell 1983, Krasowski and Nudds
1986, Crabtree et al. 1989). These discrepancies may be caused by site-specific
differences and the role of vegetation in discouraging movements of nest predators or
inhibiting visual or olfactory detection of prey (Gilbert et al. 1996). Cowardin et al
(1985) concluded that foraging efficiency of duck nest predators is further reduced by
more dispersed nests in combination with vegetation offering good concealment
characteristics.
Clark and Nudds (1991) suggested that the amount of concealment of nests
was important to duck nest survival in the prairies only when predation was
predominantly by birds. However, findings from this study do not agree with their
suggestion because destruction of mallard nests by avian predators was only observed
in two cases.
57
MANAGEMENT AND RESEARCH IMPLICATIONS
As continental waterfowl populations decline because of loss and degradation
of wetland habitat in major breeding areas of Canada, production in secondary, local
breeding areas has become increasingly important (Bartonek et al. 1984). Secondary
breeding areas (western states and provinces) support low to modest densities of ducks
over large areas and in total may make substantial contributions to annual, continental
production. This scenario maybe particularly true for mallards primarily breeding in
the Prairie Pothole Region (PPR) of northcentral U.S. and southcentral Canada.
Wetlands in the PPR have been, and continue to be, lost to agricultural activities.
Combined with prolonged drought conditions, continental mallard populations
declined about 45% between 1970 and 1990 (Caithamer and Dubovsky 1997).
Although populations have recovered significantly during the mid-1990's, continued
loss of wetlands and periodic drought cycles across the PPR will likely depress many
duck populations again. Therefore it is important that secondary populations be
identified and studied to better understand the contribution these areas make to the
continental population. Once identified, these areas can be protected, restored, and
enhanced if necessary.
Mallard production in secondary breeding areas has also been
impacted by agriculture and by other human uses of the land. In the Willamette
Valley, nearly all suitable breeding areas for mallards have been altered from their
58
pre-settlement condition, yet mallard populations persist at a low to moderate level
(ODFW unpubl. data).
In this study, it was determined that ephemeral, temporary and seasonal
wetlands are important to breeding females for acquisition of needed food resources
necessary for egg production. However, due their scattered distribution and limited
availability, these wetlands types may be a limiting factor for breeding mallards.
Therefore, activities affecting these types of wetlands, including installation of
drainage structures into agricultural fields should be discouraged whenever possible.
Semi-permanent and permanent wetlands are also important as feeding, loafing and
roosting sites away from potential predators. Creation or restoration and enhancement
of existing semi-permanent and permanent wetlands would also provide vital brood
rearing habitats necessary for successful recruitment into the fall population. Wetland
preservation or restoration programs should be expanded to ensure an adequate
wetland base for future mallard and other wetland dependent species populations in
the Willamette Valley. Programs providing landowner incentives such as the Wetland
Reserve Program should be expanded whenever possible.
The low nesting success and high female mortality during the nesting season
exhibited by upland nesting mallards indicates that high quality upland cover is
limiting and is needed to protect nests and females from mammalian predators. Such
cover should feature vigorous stands of dense upright herbaceous or shrubby
vegetation and should be in patches large enough to retard the movement of predators.
Efforts should be made to increase the amount of uncultivated upland habitats and/or
59
convert adjacent cropland into uncultivated habitats to enlarge the area of available
nesting cover. However, as nest densities increase, predation rates may also increase
unless the habitat is capable of supporting an alternate prey base. Any gain in nest
success or female survival rates may be short lived unless the total area of habitat is
large enough to achieve and sustain a reasonable balance in predator and prey
populations. The annual loss of untilled upland nesting cover is a major factor that
suppresses duck production regardless of existing water conditions. Unlike water, this
has not been a fluctuating factor among the waterfowl production requirements but has
declined continuously. In addition, sizable units of untilled habitats could be
established and maintained in agricultural areas where an adequate wetland base is
already protected or where wetland restoration or enhancement programs are being
implemented. Unnecessary cultivation or disturbance of public lands, including road
right-of-ways, should be discontinued where possible. The intensity of land use
practices on unfilled habitats should be planned to provide good quality vegetation for
ground nesting birds.
Future research should address the relationship among predator community
composition and abundance, habitat type and size and nest success. Management
efforts to increase duck production need to consider habitat and predator effects
simultaneously. Management applied at the landscape level will likely be most
effective in increasing mallard production when conducted in areas where nest success
is highest. Predator populations in the Willamette Valley should be assessed to
provide current information for management decisions. Changes from a predator
60
community dominated by coyotes to one dominated by red fox can result in marked
changes in productivity of ducks and other ground nesting birds. Management
applications e.g., restoration of wetlands, planting upland nesting cover, erection of
predator barriers and intensive predator management may be appropriate. Exclusion
of mammalian predators by barrier fences around dense nesting cover has been
effective in increasing nesting success when coupled with continual removal of
predators within the fence (Lokemoen et al.
1982,
Fleskes and Klaas
1992).
However,
predator removal programs are often viewed as socially unacceptable alternatives.
Therefore, wildlife managers should implement lethal methods only as a last resort.
Sargeant et al.
(1984)
demonstrated that predation not only lowers nest survival rates
but has a major impact on survival through loss of nesting hens. My data on loss of
females corroborate his findings.
Another key unknown in mallard nesting ecology in the Willamette Valley
which warrants further study is the recruitment of young into the fall population.
Nesting success rates in the Willamette Valley are above the 15% threshold needed to
maintain a stable breeding population, based on nest survival rates alone. However,
the survival of ducklings and subsequent recruitment into the fall population is
unknown. Estimates in duckling survival rates are needed to determine recruitment
rates and more accurately predict effects of management applications on mallard
populations. Cowardin et al.
(1985)
suggested that recruitment of females into the
breeding population may be the most important factor affecting population size.
61
Because of the mobility exhibited and the sizes of home ranges used by
mallards in the Willamette Valley, design and implementation of habitat management
plans may face some difficulty due to land ownership. Proper management will
require not only the provision of suitable nesting cover, but an adequate temporal and
spatial distribution of wetland resources. Even though mallards appear to be adaptable
to habitat disturbance and/or alteration, a regional, landscape-based approach will be
needed to assure that an adequate network of suitable habitats are maintained.
Remaining tracts of uncultivated upland habitats in the valley should be protected
from cultivation and other manipulation that would reduce their value to mallards and
other ground nesting birds. The general assumption is often made that if the quality of
upland nesting cover is improved, nest success rates of ground nesting waterfowl will
increase. This assumption has been explicitly incorporated into habitat management
protection strategies of the North American Waterfowl Management Plan (U.S. Fish
and Wildlife Service 1986).
Because of the fertility of the Willamette Valley and the demand for
agricultural products (e.g., grass seed, nursery stock, Christmas trees, and vineyards)
intensive use of the valley for agriculture will likely continue. In addition, urban
growth and encroachment into farmlands continues at a rapid pace. Without
implementation of wetland and upland habitat management plans, waterfowl managers
will be faced with the problem of maintaining populations for both consumptive and
non-consumptive uses despite a habitat base that is declining in quantity and quality.
62
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APPENDICES
74
Appendix A. Habitat community type description in the Willamette Valley of Oregon
(from Kagan and Caicco 1992).
Cover type
Abbrev. Description
Agricultural cropland and
Pasture
AGRI
Low stature annual and perennial cropland and intensively grazed pasturelands.
Includes fruit tree orchards and vineyards.
Primary plants include cultivated ryegrass
(Lolium sp.), cultivated fescue
(Festuca sp.), and timothy grass
(Phleum pratense).
Urban and
industrial
URIN
A mosaic of urbanlindustrial areas and
exotic deciduous forests.
Open water
OPWA All rivers, streams and wetlands not
included in other cover type categories.
Black hawthorn riparian and
bottomlands
BLHA
Cottonwood riparian woodland CORI
Tall shrubland or short, riparian woodland
(3-6 meters tall), including partially closed
canopy to very open canopy areas with
Grasslands, sedge wetlands interspersed,
and low shrubs in the understory of the
closed canopy areas. Primary plant
species include black hawthorn
(Crataegus douglasii), snowberry
(Symphoricarpus albus), bluegrass
(Poa pratensis).
Tall, closed to partially open canopy
forest, in narrow to wide bands along
rivers and streams, with dense shrubs.
Flooding and scouring required for
Establishment. Primary plant species
include black cottonwood (Populus
trichocarpa), blue wildrye (Elymus
glaucus), and nootka (Rosa nutkana)
75
Appendix A. (continued)
Cover type
Abbrev. Description
Willow species floodplain
riparian
WIRI
Tall shrub communities with dense cover
of willows, occasionally interspersed with
wetlands, sedge meadows or moist, forb
rich, grasslands. Occurs on broad valley
floors as well as narrow riparian canyons,
along rivers and streams. Primary plants
include Willows (Salix sp.), Currants (Ribes
sp.) and bluegrass species (Poa spp.)
Reed canary grass wetland
RECA
Uniform, dense tall grassland in seasonally
flooded areas, usually lake margins.
Occurs in disturbed areas, usually margins
of shallow, man-made lakes. Primary
plant is reed canary grass
(Phalaris arundinaceae)
Hardstem bulrush-cattail marsh BUCA
Open to dense, nearly monotypic, of tall
(2 m) bulrush species. Usually found in
standing water through much of the
growing season. Occurs in marshes and
wetlands in closed basins, in a mosaic
with open water, often by lake shores.
Primary plants include Scirpus species,
cattail (Typha latifola), Carex species
and eleocharis and juncus species.
Tufted hairgrass valley prairie
Open bunchgrass prairie, with widely
spaced, tufted tall grasses and diverse
forbs between, usually seasonally flooded
from November to May. Occurs in areas
invaded by Fraxinus latfolia with fire
exclusion. Primary plants include tufted
hairgrass (Deschampsia caespitosa), and
Roerner' s fescue (Festuca romeri),
TUI-IA
76
Appendix A. (continued)
Cover type
Abbrev. Description
Oregon ash bottomland pasture ASCO
mosaic
A mosaic of bottomland alluvial riparian
forest and developed farmland and
Pasturelands. Tall, closed canopy,
Deciduous woodlands with significant
conifer invasion and a dense shrub and
forb understory interspersed with farms
and pasturelands. Primary plants include
Oregon ash (Fraxinus latifolia), red
alder (Alnus rubra), Himalayan blackberry (Rubus discolor), and Rosa sp.
Oak-Doug. fir-ponderosa pine!
pasture-urban mosaic
OAFI
Open woodland to closed canopied
forests in which Oregon white oak
Dominates, although either Douglas fir or
Ponderosa pine may be common locally.
Occurs along the periphery of the
Willamette Valley. Primary plants include
Oregon white oak (Quercus garryana),
poison oak (Rhus diversiloba), Rosa
species, Bromus species, and Saskatoon
serviceberry (Amelanichier alnfolia).
Douglas fir-Oregon white oak
forests
FIOA
Mixed forests and woodlands in which
Douglas fir and Oregon white oak are the
usual dominants and vary in proportion.
Occurs around the periphery of the
Willamette Valley. Primary plants include
Douglas fir (Pseudotsuga meziesii),
Oregon white oak (Querqus garryana),
vine maple (Acer circinatum), rip-gut
brome (Bromus rigidus) and Fragaria sp.
77
Appendix A. (continued)
Cover type
Abbrev. Description
Oak-Pacific madrone forest
OAMA Open woodland to closed canopied
forest in which either Oregon white oak
and Pacific madrone are the canopy
Dominants. Conifers are generally
restricted to ravines and small patches on
north-facing slopes. Primary plants
include Oregon white oak (Querqus
garryana), Pacific madrone (Arbutus
menziesii), sword fern (Polystichum
munitum), Bromus species, dwarf rose
(Rosa gymnocarpa), St. John's wort
(Hypericum perforatum) and Idaho
bentgrass (Agrostis idahoensis).
Mixed evergreen and broadleaf MIEV
Deciduous forest
Closed canopied lowland and montane
forest where big-leaf maple dominate.
These are primarily second-growth forests
resulting from prior timber harvest or,
Especially in the Coast Range, historic
Wildfires within the Douglas fir-western
Hemlock type. Douglas fir is nearly
Always present and may be accompanied
by several other needle-leaf conifers. The
Conifers may form a sub-canopy which is
obscured by the deciduous overstory in
aerial photographs and remote sensing
imagery. Primary plants include Festuca
species, Salal (Gaultheria shallon), Bigleaf maple (Acer macrophyllum), red
alder (Alnus rubra), Douglas-fir
(Pseudotsuga menziesii), lady fern
(Athyrium fihix-femina), Rubus species,
Vaccinium species and Rhododendron sp.
78
Appendix A. (continued)
Cover type
Abbrev. Description
Douglas fir-western hemlockwestern red cedar forest
FIHE
Closed canopied lowland and lower
montane forest in which Douglas fir is
usually the dominant tree species, although
numerous other evergreen conifers and
Deciduous trees may be abundant. These
forests generally have a well developed
shrub layer, and a rich assemblage of
ferns, forbs, mosses, and lichens. Primary
plants include Douglas fir (Pseudotsuga
menziesii), western red cedar (Thuja
plicata), western hemlock (Tsuga hetero
phylla), Oregon grape (Berberis nervosa), Pacific dogwood (Cornus nuttalii),
Salal (Gaultheria shallon), Maidenhair
fern (Adiantum pedatum), Vanilla leaf
(Achlys triphylla), Pacific bleeding heart
(Dicentraformosa) and Spiny wood
fern (Dryopteris austriaca).
79
Appendix B. Plant species recorded within 1 meter radius of mallard nests in the
Willamette Valley of Oregon, 1995-96.
Scientific name
Rubus discolor
Rhus diversiloba
Fraxinus latfolia
Juncus effusus
Dipsacus sylvestris
Veronica beccabunga
Polystichum munitum
Festuca sp.
Phalaris arundinacea
Hypericum perforatum
Conium maculatum
Lolium sp.
Ribes lacustre
Cirsium arvense
Festuca occidentalis
Phleum pratense
Vicia cracca
Anthoxanthum adoratum
Rosa gymnocarpa
Scirpus lacustris
Carex obnupta
Pseudotsuga menziesii
Festuca romeri
Dactylis glomerata
Cytisus scoparius
Cirsium edule
Scirpus microcarpus
A thyrium filix-femina
Equisteum hyemale
Symphoricarpus albus
Gaultheria shallon
Carex stipata
Rubus ursinus
Cornus nuttalli
Madia sativa
Equisetum arvense
Mentha arvensis
Boisduvalia densflora
Common name
Himalayan blackberry
poison oak
Oregon ash
common rush
teasle
American brooklime
sword fern
cultivated fescue
reed-canary grass
St. John's Wort
poison hemlock
cultivated ryegrass
black gooseberry
Canada thistle
western fescue
timothy grass
purple vetch
sweet vernal grass
dwarf rose
hard-stemmed bulrush
slough sedge
Douglas fir
Roemer's fescue
orchard grass
scotch broom
edible thistle
small-flowered bulrush
lady fern
scouring rush
common snowberry
salal
sawbeak sedge
trailing blackberry
Pacific dogwood
Chilean tarweed
common horsetail
field mint
dense-spiked primrose