Journal of Wildlife Management 74(4):778–787; 2010; DOI: 10.2193/2008-598
Management and Conservation Article
Continental Survival and Recovery
Rates of Northern Pintails Using BandRecovery Data
MINDY B. RICE, Department of Natural Resources Management, Texas Tech University, Box 42125, Lubbock, TX 79409, USA
DAVID A. HAUKOS,1 Department of Natural Resources Management, Texas Tech University, Box 42125, Lubbock, TX 79409, USA
JAMES A. DUBOVSKY, Division of Migratory Birds and State Programs, United States Fish and Wildlife Service, Denver, CO 80225, USA
MICHAEL C. RUNGE, United States Geological Survey, Patuxent Wildlife Research Center, 12100 Beech Forest Road, Laurel, MD 20708, USA
ABSTRACT Unlike other North American prairie-nesting dabbling ducks, northern pintail (Anas acuta) populations have not increased
since the early 1990s and remain well below the long-term average for traditional survey areas. Previously reported estimates of annual survival
and recovery rates for pintails did not investigate any spatial or temporal factors to explain annual variation of these rates. We used bandrecovery data from 1970 to 2003 to test the influence of temporal periods defined by differing harvest regulations and habitat conditions of
breeding grounds with spatially delineated regions on survival and recovery rates of northern pintails in North America. We separated regions
based on a multiresponse permutation procedure to identify banding blocks with dissimilar recovery distributions based on a cluster analysis.
We categorized time by grouping years into temporal periods based on bag limits, season lengths, or overflight versus nonoverflight years. We
used the Brownie approach in Program MARK to evaluate 46 a priori models estimating survival and recovery rates. The best approximating
model indicated that survival varied with age, sex, and region with additive time and interactive time-by-age and time-by-region effects.
Recovery rate was best represented by a fully interactive term comprised of age, sex, region, and year. There were no statistical differences
among average annual survival point estimates between age and sex classes within each region, and our estimates were similar to previous
unpublished studies. We found the eastern region had decreased survival and increased recovery rates compared to other regions. Trends in
pintail survival suggest that variation in annual survival was not the cause of the initial decrease in the northern pintail population and is unlikely
the dominant factor preventing the population from increasing. The influence of other population parameters, such as recruitment rate, should
be investigated to further evaluate other causes for the population status of northern pintails. Use of the top-ranked model to estimate annual
survival and recovery rates for northern pintails in North America, which indicated that annually varying estimates of survival rates were better
supported by the data than grouping years into temporal classes (i.e., based on bag limits, season lengths, and overflight yr) can be used by
managers and policy makers when considering annual harvest regulations and effects of conservation efforts. Managers should incorporate these
estimates into future demographic studies of pintails as well as consider using the top-ranked model for future analyses of band-recovery data.
KEY WORDS Anas acuta, banding, Brownie model, harvest, North America, northern pintail, recovery, survival.
Nearly all prairie-nesting dabbling duck species have
increased in abundance since the early 1990s except
northern pintail (Anas acuta), which decreased from an
estimated 9.6 million in 1955 to 2 million by 1988 and has
remained low since then (Hestbeck 1993a, b; Sheaffer
2003). By 2002, pintails were at a low of 1.8 million birds in
the traditional survey area despite restrictive bag limits (but
not season lengths) since 1998 (Runge and Boomer 2005,
Zimpfer et al. 2008). By 2007 the estimate of pintails in the
traditional survey area had increased to 3.3 million birds, but
it declined again to 2.6 million birds by 2008 (Zimpfer et al.
2008). Despite the increase since 2002, the 2008 population
estimate was 36% below the long-term average (1955–2007,
average no. 5 4.1 million) and 54% below the goal of 5.6
million stated in the North American Waterfowl Management Plan (U.S. Fish and Wildlife Service and Canadian
Wildlife Service 1986). Although the pintail remains the
most abundant duck in the Pacific Flyway, numbers are only
25% of levels recorded in the 1970s (Fleskes et al. 2002).
The continued low abundance of pintails has caused concern
among managers as evidenced by the United States Fish and
Wildlife Service (USFWS) declaring the northern pintail a
focal species targeted for increased management emphasis
1
E-mail: david.haukos@ttu.edu
778
and the development of a species-specific harvest management strategy (USFWS 2007).
To aid in reaching the population goal of the North
American Waterfowl Management Plan, a comprehensive
evaluation of available pintail data is necessary (Podruzny et
al. 2002). Previous studies investigating survival and
recovery rates for pintails focused on annual estimates using
simple interactive models, but other factors may be
influencing these rates (Sheaffer et al. 1999, Runge and
Boomer 2005). Additional predictor variables may better
explain patterns of annual survival and recovery rates for
northern pintails. For example, previous studies have found
substantial temporal and regional variation when estimating
short-term survival rates of pintails (e.g., Nicolai et al.
2005).
Long-term trends in the pintail breeding population vary
regionally, and studies on other waterfowl species support
the concept that spatial variation is an important factor in
survival analyses (e.g., Pollock and Raveling 1982, Sedinger
and Rexstad 1994; Miller and Duncan 1999). Recent studies
of pintail survival and recovery rates focused on specific
regions, but combining and comparing data across regions
may provide additional insight (Fleskes et al. 2002, 2007;
Podruzny et al. 2002; Nicolai et al. 2005). For example, the
number of pintails in Alaska, USA, has remained constant,
whereas numbers in the Prairie Pothole Region of Canada
The Journal of Wildlife Management N 74(4)
METHODS
We obtained banding and recovery data for normal, wild
pintails from the United States Geological Survey Bird
Rice et al. N Survival of Northern Pintail
Banding Laboratory (BBL) for 1970–2003. Banding data
were comprised of all pintails in North America and we
grouped records according to age and sex. For analyses, we
included only birds banded during July–September prior to
the general waterfowl hunting season (preseason). Adequate
postseason banding data were limited to wintering areas of
western United States principally from 1970 to 1979, and,
therefore, were unavailable for our continental analyses.
Recovery data were comprised of all pintails shot or found
dead during the hunting season in North America and
reported to the BBL.
To account for potential spatial variation in demographic
rates, we stratified recovery data from banding degree blocks
into geographical units and pooled data within these units in
subsequent analyses (Royle and Dubovsky 2001). We first
compared geographic distributions of all direct (i.e.,
recovered the hunting season following banding) and
indirect (i.e., recovered 1 hunting season after banding)
pintail recoveries (ages and sexes combined) reported to the
BBL from birds banded during 1970–2003 among all
banding degree blocks using a multiresponse permutation
procedure (MRPP; Zimmerman et al. 1985, Biondini et al.
1988). We entered MRPP test statistics from all possible
pair-wise comparisons of banding degree blocks into a
dissimilarity matrix and clustered banding degree blocks
using Ward’s method in Program CLUSTAR (Romesburg
and Marshall 1980). We then developed groups of blocks
with similar recovery distributions by identifying joining
points of branches of the dendrogram resulting from the
cluster analysis. The first abrupt increase in distance
between joining points in the dendrogram suggested 12
groupings of banding degree blocks. We achieved successive
groupings by joining clusters at subsequent abrupt changes
in the joining points of the dendrogram, which resulted in
additional groupings of banding degree blocks that corresponded to 6, 5, and 3 potential geographic regions for
pooling of data and subsequent analyses. However, bandrecovery data for the 12-, 6-, and 5-region groupings were
insufficient to fit survival models and test for differences
among regions. Thus, although heterogeneity in demographic rates may be present at finer scales (i.e., many
groupings), due to data limitations we used the 3-region
delineation for all subsequent analyses. We labeled these
regions as western, central, and eastern in assessments of
spatial heterogeneity in recovery and survival rates (Fig. 1).
We included annual survival models in our model set, but
we were also interested in how other temporal periods
influenced pintail survival. Therefore, we grouped years into
temporal periods based on bag limits, season lengths, and
overflight versus nonoverflight years. We used Federal
hunting frameworks (i.e., pintail bag limits and season
lengths) to group years into temporal periods; because
Federal framework patterns were similar among Flyways,
these relative groupings were relevant for all tested regions.
For each year, we classified bag limit and season length
frameworks into 1 of 3 classes based on relative liberal,
moderate, and restrictive regulations (Table 1). However,
note that these temporal classifications were not related to
L
continue to be below the long-term average (Nicolai et al.
2005). In addition, avian survival rates within geographic
strata have shown a small effect of location for mallards
(Anas platyrhynchos) and available survival and recovery rates
for pintail do not consider regional differences (Nichols and
Hines 1987, Sheaffer et al. 1999, Runge and Boomer 2005).
Temporal variation may also contribute to observed
patterns of annual estimates of survival and recovery rates.
Confidence intervals of available annual survival and
recovery estimates are large, making it difficult to evaluate
changes in annual survival over time (Runge and Boomer
2005). Previous work suggested little evidence of significant
differences in annual survival estimates but did find evidence
for long-term patterns (Hestbeck 1993a, b). Rogers et al.
(1979), using hunting regulations for mallards, classified
years into liberal and restrictive periods of harvest to
investigate long-term patterns in survival and recovery rates.
Determining the effect of periods of differential harvest
regulations on pintail populations depends on models that
describe the relationship between regulatory decisions (i.e.,
bag limits and season length) and population parameters of
interest (Conroy et al. 2005). Relationships between
hunting frameworks and annual survival are not clear for
pintails and should be assessed (Miller et al. 1995).
One consideration for identifying patterns of survival and
recovery rates is the apparent long-term northward shift of
the mean location for the northern pintail breeding
population by 2.4u latitude (Runge and Boomer 2005).
Furthermore, during dry periods as tracked by the May
Waterfowl Breeding Survey in the Prairie Pothole Region,
pintails settle farther north in response to declining
availability of suitable breeding habitat (Smith 1970, Runge
and Boomer 2005). These long- and short-term responses
to habitat conditions may have an effect on survival and
recovery estimates. Two studies found that average latitude
and breeding population size were important predictors of
future recruitment (Sheaffer et al. 1999, Runge and Boomer
2005). Runge and Boomer (2005) found that correcting for
average latitude of the pintail breeding population fit the
observed annual fluctuations of pintail numbers since the
mid-1970s. Classification of overflight and nonoverflight
years may provide another temporal influence to account for
differences in survival and recovery rates.
The population of the northern pintail has declined, but
the underlying reasons for this trend remain unclear.
Existing survival and recovery estimates for pintails do not
include regional or temporal differences that could better
explain variation in survival (Runge and Boomer 2005). Our
objectives were to investigate additional spatial and temporal
parameters that may influence variability of annual survival
and recovery rate estimates and evaluate precision of selected
models to improve the current information being used for
monitoring and conservation of the northern pintail in
North America.
779
Table 1. Annual classification based on bag limits, season length, and
overflight years based on regulations in the Central Flyway we used in
analysis of northern pintail band recoveries in North America, 1970–2003.
Overflightc
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
moderate
moderate
moderate
moderate
moderate
liberal
liberal
liberal
liberal
liberal
liberal
liberal
liberal
liberal
liberal
moderate
moderate
moderate
restrictive
restrictive
restrictive
restrictive
restrictive
restrictive
restrictive
restrictive
restrictive
moderate
restrictive
restrictive
restrictive
restrictive
restrictive
restrictive
moderate
moderate
moderate
moderate
moderate
moderate
moderate
moderate
moderate
moderate
moderate
moderate
moderate
moderate
moderate
moderate
moderate
moderate
restrictive
restrictive
restrictive
restrictive
restrictive
restrictive
restrictive
moderate
moderate
liberal
liberal
liberal
liberal
liberal
moderate
moderate
nonoverflight
nonoverflight
nonoverflight
nonoverflight
nonoverflight
nonoverflight
nonoverflight
overflight
nonoverflight
nonoverflight
overflight
overflight
nonoverflight
overflight
overflight
overflight
nonoverflight
overflight
overflight
overflight
overflight
overflight
overflight
overflight
nonoverflight
nonoverflight
nonoverflight
nonoverflight
overflight
nonoverflight
overflight
overflight
overflight
overflight
a
Liberal ( 10 bird bag), moderate (3–5 bird bag), and restrictive (1 bird
bag).
b
Liberal ( 74 days), moderate (50–60 days), and restrictive (39 days)
based on Federal frameworks.
c
Overflight (.54.93u) and nonoverflight (,54.93u) based on average
latitude of pintails during the May Waterfowl Population Survey.
survival estimates of 1970 and 2002 and recovery estimates
of 1970 due to unreliable estimates that are typically
produced at the beginning and end of banding periods
(e.g., survival estimates
1.0; Brownie et al. 1985).
Inclusion of these estimates could bias the resulting trends.
We developed the a priori candidate model set based on
the sources of variation of interest, which included age, sex,
temporal period (yr, season length, bag limit, and breeding
latitude), banding region, and band type based on pre- and
postinternet and phone reporting. We considered both
interactive and additive effects, which resulted in 46
potential models. We discriminated among models and
selected the best approximating model using adjusted
Akaike’s Information Criterion (AICc; Anderson et al.
1998). Use of AICc provided an estimate of the expected
relative distance between the fitted model and the unknown
processes that generated observed data (Burnham and
Anderson 2002). This generalized approach can be used
with both nested and nonnested models (Williams et al.
L
780
Season lengthsb
L
similar categorical distinctions as developed in the formal
Adaptive Harvest Management process used for setting
annual harvest frameworks (Johnson 2001). The periods for
bag limits we used were similar to those used by Sheaffer et
al. (1999). We divided the overflight category into 2
periods using average latitude of pintails during the May
Waterfowl Breeding Survey to divide periods following
Runge and Boomer (2005; Table 1). We included band
type to account for potential changes in band-reporting
rates on recovery rate estimates for the period before and
after implementation of the internet and toll-free telephone
number for reporting bands, which may provide insight
into whether the increased reporting rate and new
reporting methods influenced estimates of survival and
recovery rates (M. Knoff, United States Fish and Wildlife
Service, unpublished data).
We developed a number of models a priori based on
experience of previously tested models in pintail band
recovery analyses and hypothesized relationships between
survival and temporal and spatial variables. We used the
Brownie approach in Program MARK (White and Burnham 1999) to estimate survival and recovery rates. Survival
probability is the probability that a banded bird in year t
survives to the midpoint of the banding period in year t + 1.
Recovery probability is the probability that a banded bird
was shot, recovered, and reported during the hunting season
in year t. When reporting trends and averages, we removed
Bag limitsa
L
Figure 1. The 3-region groupings of preseason banding geographic areas
from the multiresponse permutation procedure analysis based on band
recovery locations of northern pintails in North America between 1970 and
2003. Different shades indicate different recovery distribution patterns
resulting in grouped banding reference areas forming the indicated regions.
Yr
The Journal of Wildlife Management N 74(4)
Table 2. Mean annual and total number of continental bandings and recoveries in the delineated central, eastern, and western banding regions for each age
and sex class of northern pintails in North America from 1970 to 2003.
Banded
Region
Recovered
Total
Age and sex class
Mean no./yr
Range
Mean no./yr
Range
Banded
Recovered
Ad F
Ad M
Immature F
Immature M
1,153
1,666
1,335
1,329
348–2,309
222–4,155
222–3,119
298–3,486
42
148
76
135
17–83
54–277
15–147
43–341
39,210
56,644
45,389
45,185
1,442
5,047
2,575
4,600
Ad F
Ad M
Immature F
Immature M
1,283
1,272
1,048
920
369–3,756
392–3,456
355–2,655
268–2,238
45
87
60
82
17–153
23–269
12–142
20–18
43,617
43,248
35,643
31,286
1,534
2,950
2,025
2,779
Ad F
Ad M
Immature F
Immature M
77
42
120
115
12–418
11–124
27–325
16–336
6
5
14
17
1–29
0–11
4–36
5–37
2,615
1,442
4,069
3,904
197
157
477
587
Western
Central
Eastern
2002). In addition, we tested for goodness-of-fit for our
universal model using the median c-hat and deviance plot
from Program MARK.
We used Program CONTRAST (Sauer and Williams
1989) to compare survival and recovery rates among age and
sex classes among any identified spatial or temporal groups
included in the top-ranked model using their associated
standard errors. We used survival and recovery estimates
from the top model and averaged them for each age and sex
class to compare groups. We also used Program CONTRAST to compare our survival estimates with those
reported by Runge and Boomer (2005) and Sheaffer et al.
(1999). Both of these analyses used an age 3 sex interaction
to estimate annual survival and recovery rates, so we
compared only age and sex classes.
RESULTS
We used 352,252 banding records and 24,370 recovery
records for our analyses. The 3 banding regions identified
from the MRPP analysis and used in our model generation
were largely consistent with the administrative Flyway
boundaries (Fig. 1). Essentially, the western region represented the Pacific Flyway, the eastern region corresponded
with the Atlantic Flyway, and the central region reflected
the combined Central and Mississippi Flyways. Of the total,
53% of birds were banded in the western region, 44% in the
central region, and 3% in the eastern region (Table 2).
Overall, the percentage of birds recovered and reported
across all age and sex classes from 1970 to 2003 was 6.9%.
The best approximating model indicated that survival
varied with age, sex, and region with additive time, plus
interactive time 3 age and time 3 region effects (Table 3).
The associated recovery rate was supported by the fully
interactive term of age, sex, region, and year. The best
approximating model had an AICc weight of 0.998,
indicating it was clearly the best supported model within
the model set (Table 3). The next highest ranked model,
with an AICc weight of 0.002 and a DAIC of 12.31 included
an age and sex interaction, additive region effect, and an
Rice et al. N Survival of Northern Pintail
interactive effect of overflight, bag limit, and season length
(Table 3). The 10 top models contained both interactive
and additive effects for estimation of survival rates, whereas
simpler models with fewer parameters were not supported
by the data. Recovery rates of all of the highest ranked
models were best represented by the fully interactive term of
age 3 sex by region 3 year. However, dominance of the
top-ranked model in the model set precluded further
consideration of any succeeding model. In addition, the
global model fit the data, because the deviance plot
indicated a lack of trend in the pattern of residuals and
the median c-hat was 1.1. Band type and other tested
classifications had no effect on variation in recovery rates.
To identify any patterns or trends from the top model, we
compared survival and recovery rates for each additive term.
In the age, sex, and region interaction, survival for immature
females was 28% lower than adult males across regions (x23
5 10.06, P 5 0.002). There were no differences in survival
among age and sex classes within each individual region
(central: x23 5 4.88, P 5 0.18; western: x23 5 5.91, P 5
0.12; eastern: x23 5 2.33, P 5 0.51). In addition, there were
no differences in estimated survival among regions for adult
females (x22 5 0.26, P 5 0.88), immature females (x22 5
0.29, P 5 0.87), adult males (x22 5 0.06, P 5 0.97), or
immature males (x22 5 1.03, P 5 0.60; Fig. 2). For each age
and sex class, the eastern region tended to have the lowest
survival-rate point estimates, on average 12% lower, whereas
estimates for the central and western regions were similar.
Therefore, to investigate the possible influence of the
eastern region driving the inclusion of the region variables in
our models, we tested the entire model set without the
eastern region. The resulting top-ranked model was no
different than when we included the eastern region and the
top model remained the same with the survival varying with
age, sex, and region with additive time plus interactive time
3 age and time 3 region effects. The top model including
the eastern region had an AIC value of 257,706.8 and a
deviance of 5,435.8, whereas the top model without the
eastern region included had an AIC value of 245,063.5 and
781
Table 3. Model set results of the 20 top-ranked models based on adjusted Akaike’s Information Criterion (AICc) from Program MARK we used to analyze
banding recoveries of northern pintail banded in North America, 1970–2003. We used variables of interest to estimate survival and recovery rates by age (a),
sex (s), region (r), band type (bt), year (t), and temporal classification of years based on bag limit (bl), season length (sl), and relative latitude of breeding
population (of).
Survival
s3r+t+a3t+r3t
s + r + bl 3 sl 3 of
s3r+t+a3t+s3t+r3t+a3r3t+a3r3t
s3r+t+a3t+s3t+r3t+a3s3t
s3r+t+a3t+s3t+r3t+s3r3t
s3r+t+a3t+s3t
s3r+a3t+s3t+r3t+a3s3t+s3r3t
s3r+a3t+s3t+r3t+a3s3t+a3r3t
s3r+a3t+s3t+r3t+a3s3t+a3r3t+s3r3t
s 3 r 3 of 3 bl 3 sl
s3r+t+a3t+s3t+r3t
s 3 r 3 of
s3t
s3r3t
s3r3t
s3r3t
s3r3t
s3r3t
s3r3t
s3r3t
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
a
D 5 change in AICc, wi 5 wt of model, and K5 no. of parameters.
a deviance of 4,405.2. Survival and recovery rate estimates
did not differ from the model using the eastern region and
there was not an increase in precision from excluding the
eastern region.
Recovery
AICc
Da
wia
Ka
a3s3r3t
a3s3r3t
a3s3r3t
a3s3r3t
a3s3r3t
a3s3r3t
a3s3r3t
a3s3r3t
a3s3r3t
a3s3r3t
a3s3r3t
a3s3r+t
a3s3r3t
a3s3r3t
a3s3r+t
a 3 s 3 bt 3 r + t
a 3 s 3 bt + r + t
a3s+r+t
a 3 s + bt + r + t
a 3 s + bt + t + r
257,706.80
257,719.11
257,748.01
257,758.25
257,806.02
257,807.37
257,812.98
257,846.61
257,869.95
257,874.68
257,875.94
257,894.80
257,908.39
257,926.70
258,025.72
258,030.73
258,049.01
258,139.12
258,196.05
258,218.46
0.00
12.31
41.21
51.45
99.22
100.57
106.18
139.81
163.15
167.88
169.14
188.00
201.59
219.90
318.92
323.93
342.21
432.32
489.25
511.66
0.998
0.002
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
548
438
707
612
644
516
676
676
740
665
580
81
540
804
441
453
438
435
436
469
The additive time effect indicated a slight increase in
survival over time when we combined all age and sex classes
(Fig. 3). The age 3 time interactive term indicated a longterm increase in adult survival but essentially no change in
Figure 2. Annual survival rate estimates for the central, western, and eastern regions for adult male, immature male, adult female, and immature female
northern pintails, based on band-recovery data from North America, 1970–2003.
782
The Journal of Wildlife Management N 74(4)
Figure 3. Annual survival estimates of northern pintails from 1971 to 2001 based on band-recovery data from North America.
M
DISCUSSION
Two of the 3 interactive terms in our top model were
influenced by region. Survival estimates in the eastern region
have increased slightly over time, whereas they have
remained unchanged in the other 2 regions. With only 3%
Rice et al. N Survival of Northern Pintail
of total banded birds originating from the eastern region,
the estimated 11.8% recovery rate in the eastern region was
high compared to 6% in the central region and 7.3% in the
western region. Considering there were ,20 recoveries
reported annually in each age and sex class for the eastern
40 recoveries in the other 2 regions, the
region, and
disparity of recoveries may have influenced the resulting
annual survival estimates. It does not appear that annual
survival and recovery rates or temporal patterns differed
between the central and western regions. Given the
considerable inter- and intra-annual movement of pintails
within and among these regions, the lack of differences
between the central and western regions was not unexpected
(Miller et al. 2005).
Although there were long-term temporal patterns for
annual survival rates in the top-ranked model, the resulting
trends appear to be insufficient to explain the current
population status. Other studies also found little temporal
variation in annual survival probabilities for waterfowl
(Gould and Nichols 1998, Franklin et al. 2002). Current
models in place for northern pintails use corrected breeding
population estimates to develop harvest and hunting
regulations (Runge and Boomer 2005, USFWS 2007).
Those data indicated that northern pintails were moving
farther north during dry years, but our models suggest that
this movement has no apparent overall effect on female
pintail survival. However, it is possible that annual
recruitment is reduced by the movement further north as
females delay or fail to initiate nesting, although this
L
immature survival (Fig. 4). The region and time interactive
effect indicated survival in the eastern region steadily
increased, whereas there was no change in survival for the
western and central regions (Fig. 5). Average annual survival
rate for adult males was 0.759 6 0.08, for immature males
was 0.653 6 0.08, for adult females was 0.65 6 0.10, and for
immature females was 0.536 6 0.08.
The top model, and succeeding 14 ranked models,
included an age, sex, region, and time interaction for
estimation of recovery rates. Recovery rates differed among
regions (x22 5 11.02, P 5 0.004) with greater rates in the
eastern region compared to both the central and western
regions (Fig. 6). Among age and sex classes, there were
differences in recovery rates in the central and western
regions but not in the eastern region (central: x23 5 18.26, P
5 0.004; western: x23 5 27.67, P
0.001; eastern: x23 5
3.55, P 5 0.31). This relationship seemed to be driven by
adult females, which had a lower recovery rate than the
other age and sex classes in both the central and western
regions. Recovery rates of the other sex and age classes were
similar within regions (Fig. 6). Recovery rates were greater
for all age and sex classes in the eastern region and generally
higher for males than females across regions (Fig. 6).
783
Figure 4. Age 3 time annual survival estimates of adult and immature northern pintails from 1971 to 2001 based on band-recovery data from
North America.
hypothesis requires additional investigation. Apparently, any
mortality resulting from increased energetic cost related to
overflights is offset by the lack of mortality typically related
to the stress of reproduction. In addition, standard errors
and confidence intervals of annual survival estimates may be
too large to detect any noticeable temporal trends due to
hunting regulations related to bag limits and season length.
Our analyses do not support inclusion of any temporal effect
based on years grouped into classes other than annual
variation when estimating survival and recovery for pintails
across North America.
Although temporal groupings of harvest regulations based
on bag limits and season lengths did not appear to affect
survival estimates, evaluation of the effect of harvest on
annual survival was beyond the scope of our investigation.
First, recovery rates may not be good surrogates for harvest
rates because of potential but unknown temporal and
geographic differences in band-reporting rates (e.g., Nichols
et al. 1995). Even if we were to make the simplifying
assumption that such differences do not exist, we also note
that pintail harvest regulations have become more restrictive
as pintail abundance declined, which confounds the ability
to draw strong inferences between harvest rates and survival
rates. Experiments such as those advocated by Anderson et
al. (1987) and Conroy and Eberhardt (1989) would be
necessary to adequately evaluate the impact of harvest
pressure on survival. Continued development of a harvest
strategy for northern pintails could include an approach that
784
does not allow harvest regulations to co-vary with pintail
abundance, which could potentially promote a better
assessment of the impacts of harvest on annual survival of
pintails.
We compared our estimates of survival for each age and
sex class to a recent study completed by Runge and Boomer
(2005). We found no differences in estimated survival rates
for adult males (x21 5 0.012, P 5 0.91), immature males
(x21 5 0.016, P 5 0.73), adult females (x21 5 0.001, P 5
0.97), or immature females (x21 5 0.61, P 5 0.44) between
studies. There were also no differences in recovery rates for
adult females (x21 5 0.79, P 5 0.37), immature males (x21
5 0.002, P 5 0.89), and immature females (x21 5 1.63, P 5
0.20) between studies. The recovery rate difference between
studies was marginal for adult males (x21 5 3.38, P 5 0.07).
We also compared our updated survival rates using bag
limits as the temporal classification to Sheaffer et al. (1999),
in which survival was broken into similar periods from 1979
to 1992 (Table 4). We found no differences between the 2
studies in survival rates for adult females (x21 5 3.99, P 5
0.55) or adult males (x21 5 0.88, P 5 0.77). However, we
did find that survival estimates differed between the 2
studies for the moderate period for immature females (x21 5
4.24, P 5 0.04) and were marginally different for immature
males (x21 5 2.65, P 5 0.10).
Another goal of our study was to increase precision of
survival and recovery rates by accounting for additional
potential sources of heterogeneity. We found no increase in
The Journal of Wildlife Management N 74(4)
Figure 5. Time 3 region annual survival estimates of northern pintail from 1971 to 2001 in the identified western, central, and eastern regions based on
band-recovery data from North America.
Figure 6. Estimates of annual band recovery rate for the central, western, and eastern regions for adult male, immature male, adult female, and immature
female northern pintails, based on band-recovery data from North America, 1970–2003.
Rice et al. N Survival of Northern Pintail
785
Table 4. Mean survival (S) rates and associated standard errors for adult and young northern pintails in North America during periods of liberal, moderate,
and restrictive harvest regulations. Comparisons were of survival rates from liberal (1979–1984), moderate (1985–1987), and restrictive (1988–1992) years.
Liberal
Sheaffer et al. 1999
Moderate
This study
Sheaffer et al. 1999
Restrictive
This study
Sheaffer et al. 1999
This study
Age and sex class
S
SE(S)
S
SE(S)
S
SE(S)
S
SE(S)
S
SE(S)
S
SE(S)
Ad M
Ad F
Immature M
Immature F
0.765
0.619
0.677
0.683
0.010
0.015
0.030
0.044
0.749
0.636
0.673
0.566
0.088
0.113
0.056
0.058
0.735
0.671
0.811
0.779
0.018
0.028
0.055
0.078
0.737
0.620
0.658
0.540
0.087
0.105
0.081
0.091
0.807
0.658
0.739
0.538
0.014
0.022
0.059
0.069
0.780
0.679
0.636
0.512
0.071
0.082
0.092
0.101
precision using our top model for most age and sex classes.
In fact, our standard errors for recovery rates increased for all
age and sex classes, whereas those for survival rates increased
for adults and decreased for juveniles compared to those
found by Runge and Boomer (2005). Traditional models
used for pintail management have typically been based on an
age and sex class interaction without addition of interactive
spatial or temporal effects. These simpler parameterized
models were .200 AIC units from the top-ranked model
but provided similar annual estimates of annual survival
(Sheaffer et al. 1999, Runge and Boomer 2005, Lake et al.
2006). Therefore, increasing the complexity of models did
not improve precision of survival and recovery estimates.
MANAGEMENT IMPLICATIONS
Our top-ranked model indicated that multiple factors could
influence estimates of annual survival rates for northern
pintails. Inclusion of the region effect seemed to be driven
by the eastern region, where precision of estimates was low,
survival rates may be increasing over time, and recovery rates
were greater than the other 2 regions. If this regional
variation is problematic for managers developing harvestmanagement strategies, one option is to exclude data from
the eastern region when estimating survival and recovery
rates. Another option would be to increase the number of
northern pintails banded in the eastern region to increase
precision of the estimates and better define differences
among regions. This option would be expensive both in
terms of money and personnel commitments, especially for a
region with a low abundance of northern pintails. However,
given that estimates of annual survival were similar between
models with and without inclusion of a region term due to
high standard errors associated with the estimates, similar
estimates of these rates are likely to result from lessparameterized models.
Our survival and recovery rate estimates provide a
comprehensive assessment of these demographic parameters
for the continental northern pintail population. The topranked model indicated that annually varying estimates of
survival rates were better supported by the data than
grouping years into temporal classes (i.e., based on bag
limits, season lengths, and overflight yr). Managers should
incorporate these estimates into future demographic studies
of pintails as well as consider using the top-ranked model for
future analyses of band-recovery data.
786
ACKNOWLEDGMENTS
This study was funded by the USFWS Migratory Bird
Management Office and Region 2 Migratory Bird Management Office. We thank R. Blohm, M. Koneff, J. Haskins,
and J. Cornely for coordinating and administering project
funding. We thank the Pintail Action Group for contributing suggestions for data analyses and interpretation. R.
Trost, J. Fleskes, M. Koneff, and G. Boomer reviewed and
provided comments that improved earlier versions of the
manuscript.
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