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Adult pronghorn (Antilocapra americana) survival and cause-specific mortality in Custer State Park, S.D.

INTRODUCTION

Accurate estimates of sex- and age- specific vital rates are essential to understand the mechanisms driving the population dynamics of ungulates and to model the effects of management actions on population growth. The majority of literature concerning pronghorn (Antilocapra americana) vital rates focuses on neonatal survival (Canon, 1993; Avsharian and Byers, 2001; Gregg et al., 2001; Sievers, 2004; Berger and Conner, 2008) since that parameter is often most variable within ungulate populations (Galliard et al., 1998; Avsharian and Byers, 2001). However, survival of adult females is widely recognized as the most influential vital rate affecting ungulate population growth (Heppell et al., 2000; Brown et al., 2006), and when adult female survival is variable and low it may lead to population extinction regardless of neonatal survival (Gaillard et al., 2000). Natural mortality of adult males is also an important yet under-reported component of ungulate population dynamics. Low male survival can cause delayed breeding of females and thus delayed, less synchronous calvingleading to higher neonatal predation rates and lowered population growth (Mysterud et al., 2002).There is evidence that adult male survival is typically lower and more variable than adult female survival for a variety of ungulate species (Loison et al., 1999; Toigo and Galliard, 2003). Further, adult males are highly-valued by the general public for viewing and hunting (Mysterud, 2011) and data on natural mortality rates of males is important to avoid overharvest (Bender et al., 2004).

It is also necessary to identify the factors affecting survival so management actions can target underlying causes of mortality. Sources of mortality for adult pronghorn include predation (Cannon, 1995; Sievers, 2004; Jacques and Jenks, 2008; Barnowe-Meyer et al., 2009), hunter, harvest (Grogan and Lindzey, 2007; Jacques et al., 2007; Kolar et al., 2012), malnutrition, weather-related starvation (West, 1970; Barrett, 1982; Brown et al., 2006), disease (Wobeser et al., 1975; Thorne et al., 1988), fence entanglement (Harrington and Conover, 2006; Kolar et al., 2012), vehicle collisions (Gavin and Komers, 2006;Jacques et al., 2007), and parturitional complications (Jacques et al., 2007), among others. Coyotes (Canis latrans) generally account for most pronghorn predation (O'Gara, 2004a) although mountain lion (Puma concolor) predation may play a significant role in adult survival if the populations are in rugged terrain or near forested areas (Okenfels, 1994). Other predators of adult pronghorn include wolves (Canis lupus), grizzly bear (Ursus arctos horriblis), black bear (Ursus americanus), bobcats (Felis rufus), and golden eagles (Aquila chrysaetos; O'Gara and Shaw, 2004; Jacques and Jenks, 2008).

Pronghorn in Custer State Park (CSP), South Dakota, are near the northeastern edge of pronghorn range, at the ecotone between the southern Black Hills and the Great Plains. This ecotone is characterized by undulating foothills composed of mixed-grass prairie that gradually transition to steeper forested terrain. There are no published estimates of adult male survival in unharvested populations for this region, and data on natural mortality of adult females is limited to a sample size of eight radio-collared female pronghorn in Wind Cave National Park (Jacques et al., 2007). Unlike many pronghorn populations, pronghorn in CSP are not harvested, experience high levels of human disturbance, and are nonmigratory (Gary Brundige, CSP, personal communication).

Our objectives were to estimate annual survival rates and cause-specific mortality of male and female adult pronghorn in CSP and evaluate the relative importance of factors including age, sex, season, and year on survival rates using an information-theoretic approach.

METHODS

STUDY AREA

This study occurred in Custer State Park (Universal Transverse Mercator Easting 626909 Northing 4843442, Zone 13 North (43[degrees]44'45"N 103[degrees]25'5"W )), which is located in the Black Hills region of South Dakota. Custer State Park encompasses 286 [km.sup.2] and is composed primarily of forest and rangeland. Elevations range from 1146-2042 m (CSP 1995). The mixed-grass prairie and upland shrubland ecosystem, where pronghorn are typically observed, make up approximately 21% (61.05 [km.sup.2]) of CSP (CSP 1995; Fig. 1). Grasslands are dominated by Kentucky bluegrass (Poa pratensis), big bluestem (Andropogen gerardi), little bluestem (Schizachyrium scoparium), western wheatgrass (Pascopyrum smithii), blue grama (Bouteloua gracilis), sideoats grama (Bouteloua curtipendula), and sedges (Carex spp.; CSP 1995). Dominant shrub species include leadplant (Amorpha canscens), western snowberry (Symphoricarpus occidentalis), wild raspberry (Rubus idaeus), and wild rose (Rosa spp.). Pronghorn use the ponderosa pine (Pinus ponderosa) forests adjacent to grassland and fire-killed forest to a lesser extent (Fig. 1). The central forested portion of CSP is dominated by ponderosa pine which shifts to a mixture of ponderosa pine and white spruce (Picea glauca) on northern slopes and high elevations (Fig. 1). Almost 30% of CSP is burned-over forest, the results of the Galena fire of 1988, the Cicero Peak fire of 1990, and the Four-mile fire of 2008. Fire-damaged forest consists of 10,979 ha, 60% of which is fire-killed where the canopy remains primarily open (CSP 1995; Fig. 1).

A 1.54 m woven-wire fence surrounded the majority of CSP except for a portion of the northwest boundary. This fence prevents movement of bison but allows for movement of all other ungulate species into or out of CSP; pronghorn have been observed to cross the fence (B. Keller, unpublished data). There are three other internally fenced areas in CSP, which create three distinct pastures and are used to manage the distribution of bison during the roundup and to manage grazing of bison throughout the year (Fig. 1). These internal fences have a 0.4 m gap above the ground to allow pronghorn movement and pronghorn do regularly move between pastures (Barbara Keller, University of Missouri, unpublished data).

During our study period, 2005-2008, the average annual precipitation was 439.9 mm, and ranged from 78.2% to 106.2% of the 25 y mean. Approximately 82% of precipitation in CSP fell from Apr. to Sep. (Gary Brundige, Custer State Park, unpublished data). Winter in the southern Black Hills is considerably milder than elsewhere in the region and a persistent snowpack was not typically present during the study period. Average snowfall for the southern Black Hills is 114.3 cm; Mar. is the snowiest month with an average snowfall of 31.0 cm (Soil Conservation Service, 1990). Temperatures in CSP are more moderate than the surrounding plains; the average annual, summer (May-Oct.) and winter (Nov.-Apr.) temperature in CSP is 6.6 C, 13.9 C, and 0.1 C, respectively (National Oceanic and Atmospheric Administration 2001).

Approximately 800-1000 adult bison (Bison bison), 408-718 elk (Cervus elaphus), 163-279 pronghorn, 867 white-tailed deer (Odocoileus virginianus), 285 mule deer (Odocoileus hemionus), and 38-48 bighorn sheep (Ovis canadensis) occupied CSP during our study period (C. Lehman, Custer State Park, personal communication). Bison were culled annually during the fall bison roundup, as well as during several hunts during the fall. Coyotes, mountain lions, and bobcats were the major predators in CSP. Predator control in CSP during our study was limited. Coyote hunting was permitted in CSP during an 18 d season in Dec. 2005 (six coyote harvested) and 2006 (seven coyotes harvested) but due to lack of interest the season was closed in 2007 (Chad Lehman, Custer State Park, personal communication). Coyotes are not controlled in adjacent lands managed by the National Park Service and U.S. Forest Service. In South Dakota, a mountain lion harvest season occurred during our study period (Jan. 1-Mar. 31) but was limited to a harvest of 35 lions consisting of no more than 15 females in the entire state. Hunting of mountain lions was not permitted within most of CSP but was open in the small unfenced northern region of CSP. The population size of mountain lions in the Black Hills was estimated to be 250 individuals (SDGFP, 2005) during our study period.

Aerial surveys conducted on an annual basis since 2001 showed an increasing pronghorn population trend in CSP with density estimates during our study period of approximately 3.5-4.7 pronghorn/[km.sup.2] (unpublished data, Chad Lehman, Custer State Park). The CSP pronghorn population was estimated at 215 (SE = 24) individuals for 2005-2008, buck:doe ratios during the study period ranged from 0.40 to 0.64 (unpublished data, Chad Lehman, Custer State Park). The last hunting season for CSP pronghorn was in Oct. 1984 (nine day season), with a harvest of ten males and females. Pronghorn rarely leave or immigrate into CSP, although some individuals have been known to leave the park by passing under gates.

Field Methods.--We used a modified 0.308 caliber netgun (Coda Enterprises Incorporated, Mesa, AZ, U.S.A.) to capture pronghorn from a vehicle along roads throughout the prairie region of CSP (Fig. 1) between Nov. 2005 and May 2008. Pronghorn typically reside in open grasslands which allowed us to locate groups of pronghorn from a distance. We were able to approach to within 10 m of pronghorn on roads in CSP because this population was accustomed to a high level of vehicular disturbance. We also traveled off-road in the vehicle to capture pronghorn, although the paved, gravel and two-track roads covered much of pronghorn territory (Fig. 1). We determined the age of captured individuals from incisor eruption (Dow and Wright, 1962) and fitted pronghorn with radiotransmitters equipped with mortality switches (Advanced Telemetry Systems, Ishanti, MN, U.S.A.). We attempted to maintain an equal distribution of collars among both sexes.

We monitored pronghorn for mortalities approximately 3-5 times per week, between Jan. 2006 and Aug. 2008 once weekly between Nov. 2005 and Jan. 2006, and between Sep. 2008 and Nov. 2008. We determined cause of death by evaluation of the carcass. Puncture wounds on the skull are indicative of felid predation, whereas wounds on the hindquarters and throat indicate coyote predation (Halbritter et al., 2008). Caching behavior was also indicative of mountain lion predation, which was considered when the carcass was partially or completely buried (i.e., sticks, leaves, pine needles, grass, rocks, raked over carcass) or draglines were visible from kill site to cache site (Rominger et al., 2004). We also examined tracks, scat, and hair at the mortality site to determine species of predator responsible for predation events (O'Gara, 1978; Halbritter et al., 2008). If we encountered a mortality that was not fresh (no flesh left on bones, desiccated appearance) we classified the cause of death as "unknown."

Analytical Methods.--To test if our sample was biased to pronghorn that used areas close to roads, we used a Mann-Whitney test of median distance to roads between all pronghorn locations and randomly located points within the prairie habitat ([alpha] = 0.05).

We used Program MARK (White and Burnham, 1999) to estimate survival rates of pronghorn. We used the known-fate model, with a logit link function, for three seasonal intervals defined as 'small-group -parturition phase' (Mar. 16-Jul. 31), 'breeding' (Aug. 1-Oct. 31) and 'winter-grouping phase' (Nov. 1-Mar. 15). These seasons are demarcated by changes in the seasonal biology of the pronghorn based on daily observations of group sizes of pronghorn when locating marked individuals. During winter, pronghorn abandon individual territories and form large bands of males and females (O'Gara, 2004b). In CSP these bands begin to disband in Mar. as males wander alone or in small groups seeking out territories and preparing for the rut, while females give birth to fawns (mid-May to mid-Jun.; Lehman et al., 2009) and form small groups. The breeding season begins in Aug. when males defend distinct territories consisting of small harems of females (O'Gara, 2004b).

We left-censored individuals until the season they were radio-collared and we right-censored data if the transmitter failed or if an animal disappeared from the study area and was never relocated. We included animals captured within a season interval in the estimate for that season. Although this approach might bias estimates of survival upward (Pac and White, 2007), we believe this is a worthwhile tradeoff to maximize sample size.

We developed eight models in Program MARK to assess the relative importance of several factors in explaining pronghorn survival rates. We modeled survival as a function of sex and age (<4 y old and >4 y old), year (2006, 2007, and 2008), season (small group--parturition phase, breeding, and winter-grouping phase) and time from the start of the study (t). We binned ages into <4 y and >4 y old given sample size constraints and because pronghorn males typically do not acquire territories before 4 y of age (O'Gara, 2004b). We fitted reduced main-effects models for each of our biological effects, the biologically relevant time scales (year and season), a constant model and models that included an interaction term between sex, and year and between sex and season. Our saturated model included an interaction term between time (year and season), sex, and age (Table 1).

We used Akaike's Information Criterion for small sample sizes ([AIC.sub.c]; Burnham and Anderson, 2002) to assess the relative support among candidate models. We used the delta method to estimate confidence intervals for annual survival rates (Powell, 2007).

RESULTS

The capture technique we used resulted in high capture success, low mortality, and was unbiased. We captured 17 adult pronghorn in 2005 (nine males (M), eight females (F)), 20 in 2006 (eight M, 12 F), eight in 2007 (five M, three F), and five in 2008 (four M, one F), for a total of 50 radio-collared pronghorn (26 M, 24 F). Mean age at capture was 3.1 y (range = 1.5 to 7.5 y). We recorded a capture-related death rate of 4%; two pronghorn were killed during captures. Both of these animals were euthanized due to injuries sustained when the weights attached to nets hit the animal as the net was deployed. No deaths occurred <14 d after capture, and the death nearest to the capture date occurred 31 dpost-capture. We compared 8259 pronghorn locations to 8259 random locations within the prairie habitat in CSP. Random points were significantly farther from roads than pronghorn locations (U = 682,236,91, P < 0.0001). However, pronghorn were located a mean of 30-42 m closer to roads than the random points, which is not likely a biologically significant value. Therefore, our sample likely is representative of the CSP pronghorn population.

Predation was the predominant cause of death of adult pronghorn in CSP. We documented 23 deaths (10 females, 13 males) from Nov. 2005-Nov. 2008. Seven of those 23 deaths were attributed to coyote predation, nine were attributed to predation by mountain lions, and the remaining seven were unknown (Table 2). The majority of the deaths (74%) occurred during the small group -parturition season (Table 2). Mean age at death was 4.3 y (n = 23, range = 1.5 to 8.5 y). We estimated an annual survival probability of 0.801 (95% CI 0.690-0.911) for adult females and 0.760 (95% CI 0.647-0.873) for adult males. Although there was variability in survival estimates across years the 95% confidence intervals of the male and female survival estimates overlapped each year (Table 3).

The season model received the greatest support but there also was strong support for the season X sex model (Table 1). This model was driven by lower survival for the small group parturition season for both males and females compared to both the breeding season and the winter-grouping season (Table 4). The only season when confidence intervals for survival did not overlap between sexes was during the winter-grouping season, because no radio-collared females died during this season and thus adult female survival was 1.0 (Tables 2 and 4).

DISCUSSION

We observed low survival rates of adult pronghorn in CSP relative not only to the region, but to populations throughout pronghorn range. Our estimates of annual adult survival were lower than reported for harvested populations in western South Dakota (0.86; Jacques et al., 2007), for a population in southwestern Wyoming with harvest factors removed for 2003-2005 (0.82-0.85; Grogan and Lindzey 2007), and an unharvested population in Wind Cave National Park (0.87; Jacques et al. 2007). Outside of the Northern Plains region, survival of CSP pronghorn was comparable to long-term average survival for Sonoran pronghorn in the desert southwest (0.72; Bright and Hevert, 2005) although survival for Sonoran pronghorn can vary to a high of 0.92 during wet periods (deVos and Miller, 2005) to a low of 0.17 during drought conditions (Bright and Hevert, 2005), and lower than reported for northwestern Wyoming (0.91; Sawyer and Lindzey, 2000) and the Trans-Pecos region of Texas (0.85; Canon and Bryant, 2006). The lower survival of CSP pronghorn may be attributed to a high density of predators, including a geographically-isolated mountain lion population, and habitat features which facilitate predation. Our results emphasize the importance of measuring adult survival, as assumptions of high and stable adult survival of unharvested ungulate populations are not always met.

Predation rates in the CSP pronghorn population by both coyotes and mountain lions appear to be higher than elsewhere in the Northern Great Plains but similar to mortality rates observed in the Rocky Mountains and the rugged Southwest. Kolar et al. (2012) documented predation to account for 2.9% of all adult pronghorn mortalities in western North Dakota. Jacques et al. (2007) reported predation to account for 14% of all mortality for adult female pronghorn in Wind Cave National Park (WCNP), all of which was attributed to coyote predation. However, Barnowe-Meyer et al. (2009) reported that predation accounted for 59% of all adult mortalities of pronghorn in Yellowstone National Park, similar to our study. Barnowe-Meyer et al. (2009) reported similar levels of coyote predation (38% of all mortalities) and slightly lower levels of mountain lion predation (14% of all mortalities). Pronghorn rely on a predator avoidance strategy based on detecting predators in open terrain and use endurance and speed to escape them, and they are thus more susceptible to predation in areas of heavy forested cover and rugged topographical features (Byers, 1997). The Black Hills are typically

referred to as an island of rugged and forested terrain in a sea of broad open prairie. Thus mortality rates in CSP are more similar to populations in the Rocky Mountains although geographically the population is in the Northern Great Plains region. Although pronghorn can cross the boundary fence in many places in CSP, the fence limits dispersal, potentially constraining pronghorn to suboptimal habitats closer to forested and rugged features as the population increases. We were thus surprised that natural mortality of pronghorn in WCNP, which is also fenced and is adjacent to CSP, was reported to be much lower than what we observed in CSP. However, WCNP is composed of a higher proportion of prairie (83%) than CSP (21%). Thus, pronghorn may be more able to evade predators in this habitat and there may be less mountain lions using the area.

Although the amount of predation we recorded was similar to Barnowe-Meyer et al. (2009), the amount of predation we attributed to mountain lions (39% of all mortalities) was relatively high compared to most western pronghorn populations and serves as the first documentation of mountain lion predation of pronghorn in South Dakota. Mountain lion predation may be higher in CSP compared to Yellowstone National Park (Barnowe-Meyer et al., 2009) because the mountain lion population in the Black Hills is restricted to a relatively small island of forested habitat, the, predators do not compete with other apex predators such as wolves or grizzly bear, and there is a diverse prey assemblage consisting of white-tailed deer, mule deer, elk, bighorn sheep, mountain goat (Oreamnos americanus), and pronghorn as well as smaller prey including porcupine (Hystricomorph hystricidae) and wild turkey (Meleagris gallopavo) available to predators. These factors likely contributed to a mountain lion population which was dense and near saturation (Thompson, 2009) leading to higher predation rates in our study area relative to other areas in the Rocky Mountain West. During our study period, mountain lion survival was higher than elsewhere in the Black Hills (Jensen, 2011) presumably because they were not hunted in the majority of the park, and CSP may have been high quality habitat for mountain lions. However, our observations were also similar to recorded mountain lion predation in a rugged region of Arizona (38%; Ockenfels, 1994) but higher than documented in the Sonoran desert of Arizona (9%; Bright and Hevert, 2005), and the Trans-Pecos region of Texas (3%; Canon, 1995). Predation of pronghorn by mountain lions in South Dakota is likely limited to the Black Hills region as mountain lions rarely inhabit open prairie. However, mountain lions are dispersing out of the Black Hills (Thompson and Jenks, 2005; Thompson et al., 2009) and may come in contact with pronghorn populations in the prairies surrounding the region as they disperse to other areas.

There are several factors that may explain the higher mortality rates we observed during the small group -parturition season. In spring and early summer, females seek areas away from groups and with higher cover to give birth to fawns, which may make them more susceptible to predation. Higher predation of adult females in conjunction with parturition season was also observed in Barnowe-Meyer et al. (2009) and Sievers (2004) although adult female survival remained above 90% during parturition season in North Dakota (Kolar et al., 2012). In our study adult males also exhibited higher mortality during the small group-parturition season. Main and Coblentz, (1990) suggest that the prerut is a dangerous time period for males because in order to maximize body condition (and thus mating success) before the rut they may forage in habitats which provide more nutritious forage but have a higher risk of predation. Furthermore, the tendency for pronghorn to congregate in large groups during winter months increases their ability to detect and defend themselves from predators (Lipetz and Bekoff, 1982; Byers, 1997), while during the small group-parturition season pronghorn are more susceptible to predation.

We did not find that adult male survival was significantly lower than adult female survival, except during the winter-grouping season, which has important implications for harvest management. Differences in survival of adult males and females can be markedly variable among different populations of the same ungulate species (Toigo and Galliard, 2003). In general, adult male survival in ungulates is similar to adult female survival when food is not a limiting factor because males are more susceptible to starvation (Loison et al., 1999). Thus, because starvation was not a factor in adult pronghorn survival in CSP, it is logical that male and female survival should be similar. Further, if we assume that the CSP pronghorn population is not food limited, any harvest of either male or female adult pronghorn in likely to be additive. Although this population was not hunted during our study period, a harvest was re- instated beginning in 2009. CSP is classified as a unique management unit by South Dakota Game, Fish and Parks and harvest rates can thus be set for this population separate from other pronghorn populations in western South Dakota. Managers should consider that any increase in harvest of adult pronghorn in CSP may not be followed by a decrease in natural mortality.

If managers aim to increase the abundance of the CSP pronghorn population, management actions should not only be aimed at increasing neonatal survival but adult survival as well. We recommend management activities that may minimize predation on adult pronghorn during the small group-parturition season. Specifically, managing for visibility and decreasing predator hiding cover by preventing the encroachment of ponderosa pine into open areas may be beneficial. Encroachment by ponderosa pine is a management concern in CSP (CSP, 1995), and regenerating ponderosa pine can form dense thickets of "doghair" pine (Covington et al., 1997) which may serve as excellent predator cover. The mountain lion is an ambush predator, stalking prey through brush and trees or other habitats which allow mountain lions close proximity to prey for predation attempts (Hornocker, 1970; Logan and Sweanor, 2001). Habitat management which removes dense ponderosa pine on the ecotone of prairie and pine habitats may enhance pronghorn visibility while removing lion ambush cover. We recommend continued monitoring of the pronghorn population via aerial surveys to determine if such management actions are warranted. These management actions may also be beneficial to other pronghorn populations sympatric with mountain lions, such as Yellowstone National Park, and especially where hunting is permitted and harvest mortality may be additive to natural mortality.

Acknowledgments.---Funding for this research came from the South Dakota Department of Game, Fish and Parks, the Rocky Mountain Elk Foundation, and the University of Missouri. W. Beatty, C. Hansen, K. Motaz, J. Wisdom, B. Voelker, D. Mallet, J. Winski, E. Hockman, A. Johnson, and K. Asbill provided extensive field and logistic assistance. B. Gitzen, C. Rota, and two anonymous reviewers provided helpful comments that improved the manuscript.

SUBMITTED 10 JULY 2012

ACCEPTED 28 FEBRUARY 2013

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BARBARA J. KELLER (1) AND JOSHUA J. MILLSPAUGH

Department of Fisheries and Wildlife Sciences, 302 Natural Resources, University of Missouri, Columbia 65211

CHAD LEHMAN AND GARY BRUNDIGE

Custer State Park, 13329 U.S. Highway 16A, Custer, South Dakota 57730

AND

TONY W. MONG

Wyoming Game and Fish Department, 5400 Bishop Blvd., Cheyenne 82006

(1) Corresponding author: Telephone: (573)884-5245; FAX: (573) 884-5070; e-mail: KellerBJ@ missouri.edu

TABLE 1.--Model selection results for survival models of pronghorn in
Custer State Park, South  Dakota, U.S.A., 2005-2008

Model                        k (a)    [AIC.sub.c]     [DELTA]
                                          (b)       [AIC.sub.c]

{S{Season)}                    3        147.818        0.000
{S{Sex X season)}              6        149.250        1.342
{S(age)}                       2        159.217       11.399
{S(cond)}                      1        162.556       14.738
{S(year)}                      3        163.555       15.737
{S{Sex)}                       2        164.336       16.519
{S{Sex X year)}                6        168.703       20.885
{S(t (e) X season X age)}     40        187.360       39.542

Model                       [w.sub.i]     Deviance
                               (c)

{S{Season)}                   0.670        47.600
{S{Sex X season)}             0.327        42.818
{S(age)}                      0.002        61.041
{S(cond)}                     0.000        66.408
{S(year)}                     0.000        63.337
{S{Sex)}                      0.000        66.161
{S{Sex X year)}               0.000        62.271
{S(t (e) X season X age)}     0.000        0.000

(a) Number of parameters

(b) AIC, = Akaike Information Criterion for small samples

(c) Akaike weight

(d) Constant model, 1 estimate for the entire study

(e) Time from start of study

TABLE 2.--Documented number of cause-specific mortalities of
radio-collared pronghorn in Custer  State Park, South Dakota,
U.S.A., by season, Nov. 2005-Nov. 2008

                                   Cause of death

                              Coyote       Mountain lion
Season (a)                   predation       predation

Small group-parturition    4 (2 M, 2 F)     7 (3 M, 4 F)
Breeding                   2 (1 M, 1 F)     1 (1 M, 0 F)
Winter-grouping phase      1 (1 M, 0 F)     1 (1 M, 0 F)
Total                      7 (4 M, 3 F)     9 (5 M, 4 F)

                                   Cause of death

Season (a)                    Unknown           Total

Small group-parturition    6 (3 M, 3 F)     17 (8 M, 9 F)
Breeding                         0          3 (2 M, 1 F)
Winter-grouping phase      1 (1 M, 0 F)     3 (3 M, 0 F)
Total                      7 (4 M, 3 F)    23 (13 M, 10 F)

(a) Small group-parturition =.16 Mar.-31 Jul., breeding = 1 Aug.-31
Oct., and winter-grouping phase = 1 Nov.-15 Mar.

TABLE 3.--Annual survival rates of radio-collared pronghorn in Custer
State Park, South Dakota,  U.S.A., 2006-2008 (2005 not included
because pronghorn were only tracked for 2 seasons, breeding  and
winter grouping season during 2005)

Sex       Year      S        SE        95% CI

Female    2006    0.734    0.102    0.534-0.933
          2007    0.813    0.097    0.623-1.000
          2008    0.870    0.086    0.702-1.000
Male      2006    0.891    0.073    0.748-1.000
          2007    0.687    0.105    0.480-0.893
          2008    0.702    0.111    0.485-0.920
Female     ALL    0.801    0.056    0.690-0.911
Male       ALL    0.760    0.058    0.647-0.873

TABLE 4.--Seasonal survival rates of male and female radio-collared
pronghorn in Custer State Park, South Dakota, U.S.A., 2005-2008

Sex              Season (a)            S        SE         95% CI

Female    Winter-grouping            1.000    <0.001    0.999-1.000
          Small group-parturition    0.791     0.062    0.644-0.887
          Breeding                   0.977     0.022    0.858-0.997
Male      Winter-grouping            0.944     0.031    0.841-0.982
          Small group-parturition    0.837     0.053    0.706-0.916
          Breeding                   0.957     0.030    0.842-0.989

(a) Small group-parturition = 16 Mar.-31 Jul., breeding = 1 Aug.-31
Oct., and winter-grouping phase = 1 Nov.-15 Mar.
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Author:Keller, Barbara J.; Millspaugh, Joshua J.; Lehman, Chad; Brundige, Gary; Mong, Tony W.
Publication:The American Midland Naturalist
Article Type:Report
Geographic Code:1U4SD
Date:Oct 1, 2013
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