Research Article
Survival of Female Northern Pintails Wintering in the
Playa Lakes Region of Northwestern Texas
JENA A. MOON,1,2 United States Fish and Wildlife Service, Department of Range, Wildlife, and Fisheries Management, Texas Tech University,
Lubbock, TX 79409, USA
DAVID A. HAUKOS, United States Fish and Wildlife Service, Department of Range, Wildlife, and Fisheries Management, Texas Tech University,
Lubbock, TX 79409, USA
Abstract
The continental population of northern pintails (Anas acuta; hereafter pintails) has declined since the late 1970s, possibly due to poor breeding
propensity, low nest success, and low survival rates in response to habitat loss. Survival estimates are unavailable for several winter and
migration areas including the Playa Lakes Region (PLR) of northwestern Texas, USA. We investigated winter survival rates, documented periods
of mortality, and identified possible causes of mortality for 159 and 168 radiotagged female pintails during 23 October 2002–18 February 2003
and 10 October 2003–18 February 2004, respectively. We located all radiotagged pintails at least once weekly to verify survival status and usedknown fate modeling in program MARK to test the influence of capture period, female age class, body mass, and capture location on survival
rates. Cumulative survival for the 119-day period in 2002–2003 was 0.925 (95% CI ¼ 86.0–96.3). During 2003–2004, for a 134-day period,
survival estimates declined to 0.694 (95% CI ¼ 57.1–79.5). The period of highest mortality occurred during the pintail hunting season with 88%
of deaths during 2002–2003 and 34% of deaths during 2003–2004 occurring during this period. Age class and capture period did not affect
survival rates either year. There was a positive linear correlation between body mass at time of capture and survival rates during winter for 2003–
2004. The lower survival during 2003–2004 was probably due to fewer wetlands being available in the PLR. Our results suggest that habitat
conditions and hunting disturbance impact survival of pintails in the PLR of Texas. To maintain or increase wintering pintail survival in the PLR,
management should expand wetland availability to wintering waterfowl, enhance food resources, provide refuging areas, and initiate a means
for perpetual conservation of playas. (JOURNAL OF WILDLIFE MANAGEMENT 70(3):777–783; 2006)
Key words
Anas acuta, northern pintails, Playa Lakes Region, radiotelemetry, survival.
The northern pintail (Anas acuta) population has been trending
downward since the late 1970s (Miller and Duncan 1999, U.S. Fish
and Wildlife Service 2004). The 2004 breeding population estimate
of 2.2 million in the traditional survey area was a slight improvement from the all-time low of 1.8 million birds in 2002 (U.S. Fish
and Wildlife Service 2004), but these estimates remain well below
the goal of 5.6 million birds established by the North American
Waterfowl Management Plan (U.S. Fish and Wildlife Service and
Canadian Wildlife Service 1998, Miller and Duncan 1999).
The Playa Lakes Region (PLR) of northwest Texas provides
important migrating and wintering habitat for 1 million
waterfowl each year and, following the Texas Gulf Coast, is
considered the second most important wintering area for waterfowl
in the Central Flyway (Bellrose 1980, Haukos 2003). Historically,
more than one-third of Central Flyway pintails wintered in the
PLR, occasionally numbering .300,000 (Bellrose 1980). The
number of pintails wintering in the PLR has declined an estimated
47% since 1977 (Haukos 2003). However, importance of the PLR
for wintering waterfowl in the Central Flyway may be increasing
with the rapid decline of coastal habitats.
Bergan and Smith (1993) outlined the importance of the PLR
for wintering waterfowl. They reported that mallards wintering in
the PLR survived at relatively high rates compared to other
wintering areas. They found that overall female mallard survival
was highest in years of average or greater precipitation in
combination with mild winters because natural forage was
1
E-mail: Jena_Moon@fws.gov
Present address: Lower Rio Grande Valley NWR, Alamo, TX
78516, USA
2
Moon and Haukos
Pintail Wintering Survival in Texas
available in playa wetlands. They identified hunting, mammalian
predation, avian predation, and disease as important mortality
factors. Smith and Sheeley (1993) identified the advantages and
importance of good winter habitat in the PLR of Texas for
pintails. Wet years produced more natural playa habitats resulting
in pintails pairing earlier, initiating field feeding later, and
improved body condition. However, their investigations did not
estimate pintail winter survival rates.
Recently, researchers collaborated to form a number of
hypotheses that may explain declining population levels of
pintails. These include low nest success, poor breeding propensity,
disease (avian cholera [Pasteurella multocida], avian botulism
[Clostridium botulinum], lead poisoning), low breeding-season
survival of adults, habitat change, and low survival during
migration and wintering periods (Sargeant et al. 1984, Rohwer
1992, Austin and Miller 1995, Pybus and Eslinger 1996, Miller
and Duncan 1999, Guyn and Clark 2000).
Data are not currently available to estimate winter survival rates
of pintails or identify mortality factors of pintails in the PLR.
Factors affecting winter survival and mortality factors of pintails
vary geographically. Fleskes et al. (2002) reported that pintail
survival in the Central Valley of California was influenced by age,
hunting, and body mass at capture. Survival rates in California
were lower for birds wintering in the San Joaquin than
Sacramento Valley. Adult female pintails survived at relatively
high rates in the Sacramento Valley of California, where mortality
was related to molt status and caused by hunting, predation, avian
cholera and botulism, and illegal shooting (Miller et al. 1992,
1995). Cox et al. (1998) determined that hunting season and age
777
Figure 1. The study area was the Playa Lakes Region (PLR) of Northwestern Tex., USA. This region is composed of 3 major ecological regions: the Southern
High Plains (SHP), the High Plains (HP), and western portions of the Rolling Plains. The SHP region is denoted by shaded areas, the HP are all counties north of
the SHP, and the Rolling Plains area all counties east of the PLR. Trap sites are symbolized by black circles and are numbered. Trap sites 1 and 2 were used
during 2002–2003 and trap sites 3–7 represent trap sites utilized during 2003–2004. Trap site 4 represents 2 separate playa wetlands that were located closely
together.
most influenced pintail survival in southwestern Louisiana, and
primary mortality factors included legal hunting and predation. In
Sinaloa, Mexico, hunting was the main cause of pintail mortalities, but overall survival was very high (up to 94.6%; Migoya and
Baldassarre 1995).
We used radiotelemetry to estimate survival and assess causespecific mortality factors for female pintails wintering in the PLR.
We hypothesized that weekly variation in survival would reflect
hunting season, dates of field feeding, age, body mass at time of
capture, and availability of playa wetlands during the wintering
period.
Study Area
We studied pintails in the PLR of northwest Texas, USA, which
included the High Plains (north of the Canadian River), the
Southern High Plains (SHP), and a portion of the eastern adjacent
Rolling Plains ecological region (Fig. 1; Haukos and Smith 1994).
We concentrated the study in the SHP, which encompassed
130,000 km2 and contained about 20,000 playa wetlands (Haukos
and Smith 1994). The SHP had a dry steppe climate with mild
winters (Blackstock 1979), an average growing season of 180–220
days, and an average annual precipitation of 33–45 cm (Gould
1975). Most precipitation occurred in the form of rainfall with 54–
778
72% occurring during intense, localized thunderstorms from May
to September (Bolen et al. 1989). Elevations in the SHP ranged
from 1,000 to 1,200 m (Haukos and Smith 1994), with nearly level
to gently undulating topography interrupted by numerous enclosed
depressions lined by an impermeable vertisol clay, holding playa
wetlands (Blackstock 1979).
In 2002, we captured pintails in Lubbock County, Texas, on 2
privately owned wetlands; in Randall County, southwest of
Canyon, Texas, centered around Buffalo Lake National Wildlife
Refuge (BLNWR), and on privately owned playas in Oldham
County near Vega, Texas (Fig. 1). During 2003, we used 6
separate capture areas all located on private lands; 3 were located
in Randall County, Texas, and 3 in Lamb County, Texas (Fig. 1).
Habitat conditions differed during the 2 winters of our study.
The percentage of wetlands containing water during the winter of
2002–2003 exceeded that of the previous 3 winters by a factor of 2
with about 22% of playas containing enough water to support
duck use during the Midwinter Waterfowl Inventory (1–5 Jan; B.
Johnson, Texas Parks and Wildlife Department, Austin, Tex.,
USA, personal communication). However, total rainfall for 2003
was the lowest on record since 1911 (http://www.srh.noaa.gov),
and in 2003–2004, ,1% of playa wetlands contained water
The Journal of Wildlife Management
70(3)
during the Midwinter Waterfowl Inventory (B. Johnson, Texas
Parks and Wildlife Department, personal communication).
The pintail hunting season was restricted to the last 39 days of
the general duck season in our study area (107 days for other
waterfowl), with a bag limit of 1 pintail (either-sex) per day during
2002–2003 and 2003–2004. Specific seasons were 12 December
2002 to 19 January 2003, and 18 December 2003 to 25 January
2004.
Methods
Trapping and handling procedures followed guidelines outlined in
permits granted by the Texas Tech University Animal Use and
Welfare Committee (02256–07), U.S. Fish and Wildlife Service,
and Texas Parks and Wildlife Department. We captured pintails
during the falls of 2002 and 2003 using swim-in traps and rocket
nets baited with corn and hen scratch. Previous observations from
banding data indicated that birds arriving in the SHP during the
early fall (Sep–Oct) may continue south to the Texas Gulf Coast
or Mexico (Bellrose 1980). Movements of pintails outfitted with
satellite transmitters in the PLR during 2001–2003 indicated that
pintails present during November and December would likely
remain in the PLR throughout winter (Miller et al. 2003).
Therefore, to ensure an adequate sample of radiotagged pintails
would remain in the PLR, we trapped pintails during early (10–31
Oct 2002 and 2003) and late (14–28 Nov 2002 and 1 Nov–2 Dec
2003) capture periods. Through landowner cooperation, wetlands
used as capture sites were not hunted during periods of capture.
We captured and marked pintails relative to their distribution in
the PLR. We aged captured female pintails (hatch-year [HY] and
after-hatch-year [AHY]) based on plumage characteristics (Duncan 1985, Carney 1992). We used digital calipers to measure
(nearest mm) culmen length, total tarsus, middle toe length, and
head length (Dzubin and Cooch 1992). We measured flattened
wing chord using a graduated ruler. We measured body mass (þ/–
5 g) using a Pesola scale. We estimated body condition (i.e., grams
of fat) of each pintail using equations derived by Smith et al.
(1992). We attached a U.S. Fish and Wildlife Service-numbered
aluminum leg band to each pintail.
To each candidate female pintail that we captured, we attached a
backpack harness-style, 21.5-g, Very High Frequency (VHF)
radiotransmitter (Dwyer 1972) tuned for a life expectancy of 185
days; these radiotransmitters had a mercury-switch mortality
sensor with an 8-hour delay. In 2002, we held pintails for ,12
hours in a temperature-regulated facility, provided them with food
and water as needed, and released them after sunset to reduce
potential predation by diurnal predators (M. R. Miller, U.S.
Geological Survey, personal communication). During 2003, we
processed captured birds at trapping sites and released them
within 3 hours of capture. During both years, we held all captured
males and released them with radiotagged females in an effort to
maintain any established pair bonds.
We relocated radiotagged pintails weekly in vehicles outfitted
with a 4-element Yagi antennae on 4.5-m retractable masts. We
conducted aerial tracking flights every 2–4 weeks to locate missing
birds (Gilmer et al. 1981). Once located, we confirmed a bird’s
status (live or dead) and recorded the location using a Global
Positioning System. We located and retrieved carcasses within 24
Moon and Haukos
Pintail Wintering Survival in Texas
hours, depending on landowner cooperation. We examined
mortality to ascertain the cause of death, the potential predator
community or other mortality sources, and surrounding habitat
characteristics.
Survival of female pintails declines within the first few days after
capture (Cox and Afton 1998), perhaps because of capture
myopathy (Dabbert and Powell 1993) and an increased likelihood
of predation (Cox and Afton 1998). Therefore, we began survival
estimation 72 hours after we released radiotagged birds. Thereafter, we determined the survival status and location 1 time each
week for each radiotagged bird in the PLR through 18 February
2003 and 1 March 2004, the date when at least 50% of the birds
that had stayed in the PLR for the entire winter left the region
(i.e., the start of spring migration).
We established the encounter interval for survival analyses as 1
week and the experimental unit for survival as each radiotagged
bird. We estimated cumulative weekly survival (Kaplan and Meier
1958), which allowed us to pinpoint periods of high or low
mortality and compare our survival estimates to previous studies.
We used known-fate modeling in program MARK to assess the
influence of potential mortality factors affecting pintail survival
(White and Burnham 1999). Our model set consisted of survival
models that included the following predictors: 1) time; 2) capture
period; 3) hunting and nonhunting periods; and 4) field feeding
and nonfield feeding periods, with individual covariates of 5) age,
6) grams of body fat at time of capture, and 7) mass at time of
capture. We used adjusted Akaike’s Information Criterion (AICc)
scores and Akaike weights to rank and assess models (Burnham
and Anderson 2003).
Wintering waterfowl in the PLR are known to engage in field
feeding activities when wetland food resources have been
exhausted (Sheeley and Smith 1989, Smith and Sheeley 1993).
Periods of field feeding are hypothesized to affect survival rates
because of increased energy expenditures and potential exposure to
predators that occur during these periods. We considered field
feeding to be the period 12 December 2002–18 February 2003 and
11 November 2003–1 March 2004; these estimates were made by
monitoring daily movements of female northern pintails (Moon
2004). We censored birds upon the last date of location or known
emigration from the study area. Transmittered birds with known
fates after leaving the study area were not included in analysis of
survival rates for the PLR.
Results
We captured 134 female pintails using swim-in traps and 22 using
rocket nets during 2002. We radiotagged 123 female pintails
during the early-capture period (n ¼ 69 AHY, 54 HY) and 33
during the late-capture period (n ¼ 18 AHY, 15 HY). Of the 156
radiotagged pintails, 80 (51%) stayed in the PLR for the entire
study period of 10 October 2002–18 February 2003, and 41
(26%) left the PLR for 1 month but later returned to the PLR.
In 2003, we captured and radiotagged 157 female pintails in
swim-in traps and 7 in rocket nets; 112 (n ¼ 77 AHY, 35 HY)
during the early-capture period and 52 (n ¼ 33 AHY, 19 HY)
during the late-capture period. Of these, 54 (33%) stayed in the
PLR for the entire study period (8 Oct–1 Mar) and 33 (20%) left
the PLR for a period of 1 month and later returned to the PLR.
779
Spring migration occurred later during 2003–2004; therefore, we
tracked birds in the PLR for an additional 2 weeks.
We verified the death of 8 (5%) pintails during 2002–2003,
with 7 occurring during the pintail hunting season. Hunters shot 2
pintails: 1 approximately 1.6 km south of New Deal, Texas, on 6
January 2003; and 1 near Pesquerias, Mexico, on 25 January 2003
(1,025 km from the study area). Of the 6 remaining known
mortalities, we attributed 3 to predation (2 mammalian, 1 avian
predator). We were unable to conclusively determine the cause of
3 female deaths.
During winter 2003–2004, we verified 26 (16%) mortalities.
But unlike 2002–2003, mortalities occurred throughout winter,
with 9 deaths occurring during the pintail hunting season and 19
deaths during the general waterfowl hunting season. We
attributed mortalities to hunting (2), mammalian predation (7),
avian predation (12), and unknown causes (5). The first hunting
mortality, an illegal kill during the general duck season, occurred
in the PLR prior to the pintail hunting season on 12 November
2003. The second hunting mortality occurred during the pintail
hunting season on 5 January 2004, near El Campo, Texas (750 km
from the study area).
Because habitat conditions, survival patterns, and levels of
mortality differed greatly between 2002–2003 and 2003–2004, we
considered overwinter survival to be dependent on year and
modeled years separately (G. White, Colorado State University,
Fort Collins, Colo., USA, personal communication). During
2002–2003, cumulative winter survival was 92.5% (95% CI ¼
86.7–100) using Kaplan-Meier, which was indistinguishable from
the estimate provided by the top model (program MARK) of
92.6% (95% CI ¼ 86.0–96.3). The most parsimonious model
from MARK contained only pintail hunting season. This model
compared periods of pintail hunting versus nonhunting periods
(Table 1). Pintail mass, fat content, and periods of field feeding
did not improve the survival model but were worth considering
(DAIC , 2.00). The top 4 models contained the variable pintail
season and had 94% of the cumulative weights of models
considered, indicating pintail hunting season was the primary
period influencing pintail survival in 2002–2003 (Table 1).
Models that did not contain pintail hunting season were not
supported by the data. Survival varied between pintail hunting
versus nonhunting periods (Fig. 2) for 2002–2003. Weekly
survival during nonhunting periods was 99.9% (95% CI ¼ 99.3
to 100) and 98.9% (95% CI ¼ 97.7 to 100; Fig. 2) during the
pintail hunting season.
During 2003–2004, the overall Kaplan-Meier survival estimate
was 73.6% (95% CI ¼ 58.2–81.3), but the best model generated by
program MARK estimated cumulative survival at 69.4% (95% CI
¼ 57.1–79.5). The additive time þ mass model was the top-ranked
model, and it contained almost half of the total cumulative model
weight (Table 2). The top 4 models included time, and combined
they made up 99% of the cumulative AIC weights of examined
models (Table 2). Survival rates for 2003–2004 varied weekly, with
week 20 (just prior to migration; 22 Feb–28 Feb) having the lowest
survival rate for the wintering period (87.5%, 95% CI ¼ 71.1 to
95.2; Fig. 3). Because body mass improved model support, we
examined this covariate further. Overwinter survival increased as
body mass at time of capture increased (Fig. 4).
780
Table 1. Number of parameters (K), Akaike’s Information Criterion (AICc
values), AICc weights of models, and DAICc values used to rank models
containing factors or individual covariates that were hypothesized to affect the
probability of survival of female northern pintails in the Playa Lakes Region of
Tex., USA, during winter of 2002–2003 (10 Oct–18 Feb).
Modela
K
AICc
AICc weight
DAICc
Pintail season
Pintail season þ field feeding
Pintail season þ mass
Pintail season þ fat
Field feeding
General duck season
Time constant
Prehunt, hunt, posthunt
Mass
Age
Capture date
Fat
Time
Time þ mass
Time þ age
Time þ fat
2
3
3
3
2
2
1
3
2
2
2
2
18
19
19
19
97.25
98.59
99.05
99.24
102.40
103.30
104.59
105.17
106.19
106.48
106.48
106.58
118.23
120.04
120.15
120.55
0.41
0.21
0.17
0.15
0.03
0.02
0.01
0.01
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
1.34
1.79
1.99
5.15
6.05
7.34
7.92
8.93
9.22
9.23
9.33
20.98
22.79
22.90
23.00
a
Pintail season consisted of the pintail hunt and nonhunting periods in
the High Plains Mallard Management Unit; the prefield feeding period was
from arrival to 11 Dec, and the period 12 Dec to emigration was the field
feeding period; mass was measured at the time of capture; fat was the
estimated body fat at time of capture; and capture date was the period of
early capture (11–31 Oct) and late capture (14–27 Nov).
Discussion
During our study, winter survival rates of female pintails were
related to habitat conditions and the pintail hunting season. The
presence and amount of available natural foods affect survival and
body condition of pintails in the SHP (Sheeley and Smith 1989).
Pintails wintering in the SHP forage on wetland seeds such as
barnyard grass (Echinochloa crusgalli), smartweed (Polygonum spp.),
curly dock (Rumex crispus), and aquatic invertebrates in playas
until these resources are exhausted, and they then switch to waste
grain feeding in agricultural fields (Sheeley and Smith 1989).
Above-average rainfall years in the PLR, during which wetland
foods increase in playas, produce higher survival rates and
improved body condition of mallards (Bergan and Smith 1993).
Figure 2. Weekly survival distribution of the best survival model calculated by
Program MARK for female northern pintails radio-tagged in the Playa Lakes
Region of Northwest Tex., USA, and monitored 10 October 2002–18 February
2003. Dashed lines indicate lower 95% confidence intervals. All upper
confidence intervals are at or approaching 1.00.
The Journal of Wildlife Management
70(3)
Table 2. Number of parameters (K), Akaike’s Information Criterion (AICc
values), AICc weights of models, and DAICc values used to rank models
containing factors or individual covariates that were hypothesized to affect the
probability of survival of female northern pintails in the Playa Lakes Region of
Tex., USA, during winter of 2003–2004 (8 Oct–1 Mar).
Modela
K
AICc
AICc weight
DAICc
Time þ mass
Time
Time þ age
Time þ fat
Mass
Pintail season þ mass
Capture date
Field feeding
Age
Time constant
Pintail season
Fat
Pintail season þ field feeding
Prehunt, hunt, posthunt
Pintail season þ fat
General duck season
21
20
21
21
1
3
2
2
2
1
2
2
3
3
3
2
265.60
267.12
267.40
268.43
278.44
279.03
279.28
279.78
279.97
280.97
280.76
281.41
281.60
281.79
282.05
282.08
0.47
0.22
0.19
0.11
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.0
1.5
1.8
2.8
12.8
13.4
13.7
14.1
14.4
14.5
15.1
15.8
16.0
16.2
16.4
16.5
a
Pintail season consisted of the pintail hunt and nonhunting periods in
the High Plains Mallard Management Unit (HPMMU); the prefield feeding
period was from arrival to 11 Dec, and the period 12 Dec to emigration was
the field feeding period; general duck season was the period of hunting
allowed in the HPMMU; prehunt, hunt, posthunt were those periods of
pintail hunting and nonhunting in the PLR; mass was measured at the time
of capture; fat was the estimated body fat at time of capture; and capture
date was the period of early capture (11–31 Oct) and late capture (14–27
Nov).
A relationship between body condition and survival rates has not
been shown for pintails in Louisiana (Cox et al. 1998) or Mexico
(Migoya and Baldassare 1995). Our models that included body fat
or mass did not affect survival during 2002–2003; however, during
2003–2004, mass at time of capture played a major role in survival
of female pintails in the PLR.
Birds arriving during the dry 2003–2004 year were an average of
52 grams lighter than birds arriving in wet 2002–2003 for the
PLR (Moon 2004). Pintails with higher body mass survived better
during the dry year in the PLR when compared to birds with
lower body mass. The relationship between body mass at time of
Figure 3. Weekly survival distribution of the best survival model calculated by
Program MARK for female northern pintails radio-tagged in the Playa Lakes
Region of Northwest Tex., USA, and monitored 8 October 2003–1 March
2004. Dashed lines indicate upper and lower 95% confidence intervals.
Moon and Haukos
Pintail Wintering Survival in Texas
Figure 4. Relationship between body mass and survival for female northern
pintails wintering in the Playa Lakes Region of northwestern Tex., USA, from 8
October 2003–1 March 2004.
capture and survival rates during the winter of 2003–2004 indicate
timing and amounts of precipitation resulting in increased playa
quality and quantity were important to wintering female pintails
in the PLR. Similar to our results, Fleskes et al. (2002) also
reported a relationship with body mass at time of capture and
survival rates, especially for HY pintails in California. They
reported that daily odds of pintail survival increased with higher
body-condition levels. These findings indicate that HY pintails
may be less capable of improving body condition levels upon
arrival in wintering areas (Fleskes et al. 2002). In general, ducks in
good condition during winter survive at higher rates, pair earlier,
and enjoy greater breeding success than birds in poor condition
(Heitmeyer and Fredrickson 1981, Delnicki and Reinecke 1986,
Hepp 1986, Raveling and Heitmeyer 1989). Therefore, body mass
at time of capture in the PLR appears to play a much larger role in
wintering survival during dry years than wet years. Fleskes et al.
(2002), also reported that drought conditions, both on nesting and
wintering grounds, intensified low body-condition levels in
pintails and therefore decreased the likelihood of survival.
Our cumulative survival estimate for the 130-day wintering
period during 2002–2003 in the PLR was higher (92.6%, 95%
CI ¼ 86.7–100) than similar studies in other regions. Survival
estimates for 2003–2004 for a 140-day period were lower (69.4%,
95% CI ¼ 57.1–79.5) than 2002–2003, but they were still
comparable to other wintering areas. Cox et al. (1998) estimated
female survival at 71.4% (SE ¼ 4.5) for AHY birds and 55.0%
(SE ¼ 6.8) for HY birds in southwestern Louisiana during winters
of 1991–1993 for a 147-day period each year. Similar survival
estimates of 75.6% (95% CI ¼ 63.8–81.7%) and 65.4% (95%
CI ¼ 56.7–73.1%) were found for AHY and HY female pintails,
respectively, during fall and winter of 1991–1993 for a 210-day
period each year in central California (Fleskes et al. 2002). For a
187-day period during winters of 1987–1990, overall survival was
estimated at 87.4% for adult female pintails (SE ¼ 0.031) in the
Sacramento Valley, California (Miller et al. 1995). Estimated
survival of pintails wintering in Sinaloa, Mexico, was 91.0%
(Migoya and Baldassare 1995). This estimate for the winters of
1990–1992 in Mexico was for a 105-day period and was similar to
our 2002–2003 estimates.
781
Mortality factors for mallards in the PLR as reported by Bergan
and Smith (1993) include hunting (12%), mammalian predators
(14%), avian predators (12%), and unknown causes (62%). Other
natural mortality factors in the PLR, mainly disease, likely played a
role in the unknown cause of death during their study. Similar to
Bergan and Smith (1993), we found natural (i.e., nonhunting)
mortality to be the main cause of mortality within the region
(2002–2003: 6 of 8; 2003–2004: 24 of 26). Fleskes (2003) found
that although harness-style transmitters did appear to impact body
mass of some individuals, they did not have an impact on survival
or movements of pintails wintering in California. Disease
apparently was not an important mortality factor and did not
cause any deaths during our study. Furthermore, there were not any
reported major epizootic outbreaks of avian cholera and avian
botulism in the PLR during 2002–2004 (L. Nymeyer, U.S. Fish
and Wildlife Service, Buffalo Lake, Tex., USA, personal communication).
During 2002–2003, the primary period of mortality for radiotagged birds occurred during the pintail hunting season. Direct
hunting mortality in the PLR is low (P. Padding, U.S. Fish and
Wildlife Service, Laurel, Md., USA, personal communication),
when compared to other regions of Texas, with only 4% and 13%,
respectively, of known deaths attributed to hunting during our
study. In 2002–2003, for the PLR, few pintails were estimated to
be harvested by the Harvest Information Program (HIP; P.
Padding, U.S. Fish and Wildlife Service, Laurel, Md., USA,
personal communication). But, in coastal habitats in Texas—a
relatively high harvest area—50–100 times more pintails were
estimated to have been harvested for the same period (P. Padding,
U.S. Fish and Wildlife Service, personal communication). Hunting
was a significant mortality factor for wintering female pintails in
some parts of Louisiana and California (Cox et al. 1998, Fleskes et
al. 2002). In California, hunting accounted for 83% of mortalities
in the San Joaquin Valley during 1991–1994 (Fleskes et al. 2002).
Cox et al. (1998) reported that 65% of mortalities in Louisiana
were from hunting. Although survival estimates in Mexico were
high, Migoya and Baldassarre (1995) also found that hunting
caused most mortalities with only 1 known death occurring from
natural causes in Mexico.
Although direct hunting pressure is low within the region, the
period of pintail hunting likely was a high-disturbance period.
The pintail hunting season overlaps not only with the general
duck, goose, and sandhill crane (Grus canadensis) hunting seasons,
but also with the ring-necked pheasant (Phasianus colchicus)
hunting season. Because all game-bird species rely on playa
wetlands for habitat in the PLR, this may have indirect impacts on
wintering pintails. Even though hunters may not be targeting
pintails during this period, they are targeting pintail habitats
within the region. Also, depending on fall weather patterns, crop
harvest times within the region may be closely related to the dates
of the pintail hunting season, thus creating another form of
disturbance. Even with a restricted pintail hunting season during
our study, distance of female pintail daily movements doubled at
the onset of the pintail hunting season (high disturbance period)
in 2002–2003 and increased 15% during 2003–2004 (Moon
2004). Daily movement distances due to disturbance may play a
significant role in pintail energetics and survival within the region.
This increase in movements may lower body mass, which would
decrease the likelihood of survival.
Management Implications
Management of wetlands used by pintails in the PLR could help
minimize the impacts of poor habitat conditions, because playa
wetlands managed for moist-soil foods can support higher
populations of waterfowl for longer periods. We recommend that
management practices on these wetlands focus on increasing the
availability of playa basins with usable water for ducks and on
enhancing natural food resources in those wetlands during dry
winters (Haukos and Smith 1993, Anderson and Smith 2000).
Therefore, we recommend increasing habitat acquisition and
preservation of playa wetlands within the PLR. Despite acknowledgment of the value of playas to waterfowl through the creation
of the Playa Lakes Joint Venture by the North American
Waterfowl Management Plan (U.S. Fish and Wildlife Service
and Canadian Wildlife Service 1998), past management recommendations to improve wintering habitats for waterfowl have not
been implemented across the region. This in turn may have
reduced the value of the PLR for wintering waterfowl and lowered
survival rates over time. There is an urgent need for conservation
of playa wetlands due to declines in quantity and quality of these
wetlands, especially in the SHP where most playas occur (Haukos
and Smith 2003, Smith 2003).
Acknowledgments
We thank Texas Tech University, U.S. Fish and Wildlife Service
Region 2 Migratory Bird Office, Northern Prairie Wildlife
Research Center, and the Playa Lakes Joint Venture for providing
funding for this project. R. Cox, B. Johnson, B. Davis, L.
Gustafson, D. Casida, J. Smith, J. Bredy, P. Thorpe, and F.
Roetker provided field assistance during this study. L. Nymeyer
provided field technicians, vehicles, and access to trapping sites.
We appreciate the technical support and guidance for survival
analyses provided by G. White. G. Filnor, J. Heath, J. Jones, B.
Jones, M. Been, M. Montene, C. Sargent, A. McNeil, and J.
Stevens provided access to private lands for trapping efforts. In
addition, we thank all PLR landowners who allowed access to
retrieve mortalities. We also thank M. Miller, R. Cox, and L.
Smith for thorough reviews of previous drafts of this manuscript.
This is paper T-9-1041 of the College of Agricultural Resources
and Natural Resources, Texas Tech University.
Literature Cited
Anderson, J. T., and L. M. Smith. 2000. Invertebrate response to moist-soil
management of playa wetlands. Ecological Applications 10:550–558.
Austin, J. E., and M.R. Miller. 1995. Northern pintail (Anas acuta). Number 163
in A. Poole and F. Gill, editors. The birds of North America. The Academy of
Natural Sciences, Philadelphia, Pennsylvania, USA, and The American
Ornithologists’ Union, Washington, D.C., USA.
782
Bellrose, F. C. 1980. Ducks, geese, and swans of North America. Third edition.
Stackpole, Harrisburg, Pennsylvania, USA.
Bergan, J. F., and L. M. Smith. 1993. Survival rates of female mallards wintering
in the Playa Lakes Region. Journal of Wildlife Management 57:570–577.
Blackstock, D. A. 1979. Lubbock county soil survey. U.S. Soil Conservation
Service, College Station, Texas, USA.
The Journal of Wildlife Management
70(3)
Bolen, E. G., L. M. Smith, and H. L. Schramm, Jr. 1989. Playa lakes: prairie
wetlands of the Southern High Plains. BioScience 39:615–623.
Burnham, K. D., and D. R. Anderson. 2003. Model selection and multimodel
inference: a practical information–theoretic approach. Second edition.
Springer-Verlag, New York, New York, USA.
Carney, S. M. 1992. Species, age, and sex identification of ducks using wing
plumage. U.S. Department of the Interior, Washington, D.C., USA.
Cox, R. R., Jr., and A. D. Afton. 1998. Effects of capture and handling on
survival of female northern pintails. Journal of Field Ornithology 69:276–287.
Cox, R. R., Jr., A. D. Afton, and R. M. Pace, III. 1998. Survival of female
northern pintails wintering in southwestern Louisiana. Journal of Wildlife
Management 62:1512–1521.
Dabbert, C. B., and K. C. Powell. 1993. Serum enzymes as indicators of
capture myopathy in mallards (Anas platyrhynchos). Journal of Wildlife
Diseases 29:304–309.
Delnicki, D., and K. J. Reinecke. 1986. Mid-winter food use and body weight
of mallards and wood ducks in Mississippi. Journal of Wildlife Management
50:43–51.
Duncan, D. C. 1985. Differentiating yearling from adult northern pintails by
wing–feather characteristics. Journal of Wildlife Management 49:576–579.
Dwyer, T. J. 1972. An adjustable radio-package for ducks. Bird-Banding 43:
282–284.
Dzubin, A., and E. G. Cooch. 1992. Measurements of geese: general field
methods. California Waterfowl Association, Sacramento, USA.
Fleskes, J. P. 2003. Effects of backpack radiotags on female northern pintails
wintering in California. Wildlife Society Bulletin 31:212–219.
Fleskes, J. P., R. L. Jarvis, and D. S. Gilmer. 2002. September–March survival
of female northern pintails radiotagged in San Joaquin Valley, California.
Journal of Wildlife Management 66:901–911.
Gilmer, D. S., L. M. Cowardin, R. L. Duval, L. M. Mechlin, J. W. Shaiffer, and V.
B. Kuechle. 1981. Procedures for the use of aircraft in wildlife biotelemetry
studies. U.S. Fish and Wildlife Service, Washington, D.C., USA.
Gould, F. W. 1975. Texas plants—a checklist and ecological summary. Texas
Agricultural Experiment Station, College Station, USA.
Guyn, K. L., and R. G. Clark. 2000. Nesting effort of northern pintails in Alberta.
Condor 102:619–628.
Haukos, D. A. 2003. Analyses of selected mid-winter waterfowl survey data
(1955–2003). U.S. Fish and Wildlife Service, Albuquerque, New Mexico,
USA.
Haukos, D. A., and L. M. Smith. 1993. Moist-soil management of playa lakes
for migrating and wintering waterfowl. Wildlife Society Bulletin 21:288–298.
Haukos, D. A., and L. M. Smith. 1994. The importance of playa wetlands to
biodiversity of the Southern High Plains. Landscape and Urban Planning 28:
83–98.
Heitmeyer, M. E., and L. H. Fredrickson. 1981. Do wetland conditions in the
Mississippi Delta hardwoods influence mallard recruitment? Transactions of
the North American Wildlife and Natural Resources Conference 46:44–57.
Hepp, G. R. 1986. Effects of body weight and age on time of pairing of
American black ducks. Auk 103:477–484.
Kaplan, E. L., and P. Meier. 1958. Nonparametric estimation from incomplete
observations. Journal of the American Statistical Association 53:457–481.
Moon and Haukos
Pintail Wintering Survival in Texas
Migoya, R., and G. A. Baldassarre. 1995. Winter survival of female northern
pintails in Sinola, Mexico. Journal of Wildlife Management 59:16–22.
Miller, M. R., and D. C. Duncan. 1999. The northern pintail in North America:
status and conservation needs of a struggling population. Wildlife Society
Bulletin 27:788–800.
Miller, M. R., J. P. Fleskes, D. L. Orthmeyer, and D. S. Gilmer. 1992. Survival
and other observations of adult female northern pintails molting in California.
Journal of Field Ornithology 63:138–144.
Miller, M. R., J. P. Fleskes, D. L. Orthmeyer, W. E. Newton, and D. S. Gilmer.
1995. Survival of adult female northern pintails in Sacramento Valley,
California. Journal of Wildlife Management 59:478–486.
Miller, M. R., J. Y. Takekawa, D. L. Orthmeyer, J. P. Fleskes, M. L. Casazza,
and W. M Perry. 2003. Tracking spring migration of northern pintails with
satellite telemetry. Final report. U.S. Geological Survey, Western Ecological
Research Center, Dixon and San Francisco Bay Field Stations, California,
USA.
Moon, J. A. 2004. Survival, movements, and habitat use of female northern
pintails wintering in the Playa Lakes Region. Thesis, Texas Tech University,
Lubbock, USA.
Pybus, M. J., and D. Eslinger. 1996. Waterfowl disease at Pakowki Lake,
1995. Alberta Fish and Wildlife, Edmonton, Canada.
Raveling, D. G., and M. E. Heitmeyer. 1989. Relationships of population size
and recruitment of pintails to habitat conditions and harvest. Journal of
Wildlife Management 53:1088–1103.
Rohwer, F. C. 1992. The evolution of reproductive patterns in waterfowl.
Pages 486–539 in B. D. J. Bat A. D. Afton, M. G. Anderson, C. D. Ankney, D.
H. Johnson, J. A. Kadlec, and G. L. Krapu, editors. Ecology and
management of breeding waterfowl. University of Minnesota Press,
Minneapolis, USA.
Sargeant, A. B., S. H. Allen, and R. T. Eberhardt. 1984. Red fox predation on
breeding ducks in mid-continent North America. Wildlife Monographs 89.
Sheeley, D. G., and L. M. Smith. 1989. Tests of diet and condition bias in
hunter-killed northern pintails. Journal of Wildlife Management 53:765–769.
Smith, L. M. 2003. Playas of the Great Plains. University of Texas Press,
Austin, USA.
Smith, L. M., and D. G. Sheeley. 1993. Factors affecting condition of northern
pintails wintering in the Southern High Plains. Journal of Wildlife Management 57:62–71.
Smith, L. M., D. G. Sheeley, and D. B. Wester. 1992. Condition models for
wintering northern pintails in the Southern High Plains. Great Basin Naturalist
52:226–231.
U.S. Fish and Wildlife Service. 2004. Trends in duck breeding populations,
1955–2003. Office of Migratory Bird Management, U.S. Department of the
Interior, Laurel, Maryland, USA.
U.S. Fish and Wildlife Service and Canadian Wildlife Service. 1998. North
American waterfowl management plan—a strategy for cooperation. U.S.
Department of the Interior, Washington D.C., USA.
White, G. C., and K. P. Burnham. 1999. Program Mark: survival estimation
from populations of marked animals. Bird Study 46 Supplement:120–138.
Associate Editor: Ransom.
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