Shawn P. Haskell

DESERT MULE DEER SURVIVAL IN SOUTHWEST TEXAS

Abstract We studied population structure and limiting factors within a desert mule deer (Odocoileus hemionus eremicus) population in Brewster County of the Trans-Pecos Region in Texas, USA. We estimated and compared annual survival and pregnancy rates from March 1990–February 1993 for 121 adult (>33 months old) male and female, 61 subadult (21–33 months old), and 77 young (8–20 months old) deer. Variation in weather patterns (i.e., drought) was associated with—if not causative of—annual variation in survival patterns. Adult female and young survival had the strongest correlation with drought. Pregnancy status of young (≤1.5 yr) and old (≥6.5 yr) deer appeared most affected by drought. Seasonal periods of natural stress differed for adult sex classes, with most female mortalities occurring during months associated with parturition and lactation, and most male natural stress losses occurring during late winter and early spring. The major mortality sources were hunting and natural stressors for adult males, natural stressors and predation for adult females, and predation and natural stressors for young. Subadult mortalities were too few to identify significant mortality agents. The significance of natural stress-related survival and fecundity impacting herd productivity and stability warrants further consideration of poorly understood causative mechanisms. Ideally, replicated treatment areas would be used to address compensatory and additive mortality issues relative to predator abundance, harvest, and natural-stress losses.

Observations on Capturing and Aging Deer Fawns

Abstract During a study of fawn mortality of sympatric white-tailed (Odocoileus virginianus) and mule deer (O. hemionus eremicus) in west-central Texas from 2004 to 2006, we made observations that should help deer researchers increase their efficiency of capture of fawns, obtain better estimates of ages of fawns, and obtain more reliable estimates of fawn survival. We experimented with vaginal-implant transmitter designs and found that larger holding wings and antennas protruding <1 cm past the vulva resulted in more successful drops at birth sites. White-tailed fawns moved farther from birth sites than mule deer fawns of similar ages (P = 0.027). Our model predicted that white-tailed and mule deer fawns moved an average of 100 m away from birth sites after 12.5 and 17.5 h postpartum, respectively; outliers may be expected. Compared to previously published models estimating ages of captive fawns from new hoof growth, our model predicted that free-ranging fawns were generally 1.5 weeks older. As others have suggested, abandonment induced by marking was rare, and we suggest methods for monitoring does and fawns that could minimize such occurrences. Behavioral and morphological models that we describe may be species-, site-, and time-specific, and biologists should use caution when extrapolating inferences from captive animal–derived models to free-ranging populations.

Modeling the Western Arctic Caribou Herd During a Positive Growth Phase: Potential Effects of Wolves and Radiocollars

Abstract Population modeling exercises can lead to both expected and unexpected results useful for wildlife research and management, even though inferences must often be qualitative, given underlying assumptions. Our main objective was to use empirical data on wolf (Canis lupus) kill rates and growth of the Western Arctic caribou (Rangifer tarandus) herd (WAH) of Alaska, USA, to assess the potential for predator regulation. We used available data and published literature to construct a deterministic density-dependent population model fitted to trends of the WAH from 1976 through 2003. By increasing wolf densities in the baseline model, we failed to reject the hypothesis that wolves at a density of 6.5 wolves per 1,000 km2 could regulate a caribou herd at a density of 0.4 caribou per km2. In addition, our model may be conservative by underestimating the regulatory potential of wolves. We suggest that this relatively simple predator–prey system shows signs of a predation–food 2-state model. Elasticities from matrix models may be deceiving. Although herd growth is most sensitive to changes in adult female survival, survival of younger cohorts may be more easily influenced by natural conditions or management action. Management of the WAH near maximum sustained yield may not be attainable if desired, but modeling exercises such as this elucidate options. In conducting this research, we also discovered by Monte Carlo simulation that survival and productivity data from radiocollared females and calves were negatively biased and failed to predict herd growth. Thus, researchers should consider potential effects of neck collars on vital rates of female tundra caribou and concomitant offspring when using sample data to model population dynamics or test hypotheses.

Annual re-habituation of calving caribou to oilfields in northern Alaska: implications for expanding development

Previous research led to hypotheses that calving caribou (Rangifer tarandus granti J.A. Allen, 1902) in north Alaskan oilfields habituated to human activities: (i) across years and (ii) annually after spring migration (i.e., re-habituation). We used predictor variables of year and a spring snowmelt index to evaluate weight of evidence for these competing hypotheses. Response variables were calf percentage and sighting rate of calving caribou along a high-traffic road system from 1982 to 1990 and 2000 to 2002. We also considered local calf percentage and caribou density, determined by aerial surveys, for respective response variables. We found no evidence of habituation across years. We found two more lines of evidence (one strong and one weaker) for re-habituation within years during calving periods. Post hoc models suggested a further tolerance response exhibited by caribou; more data are needed. Even when snow melted early and calving caribou were most habituated among years, caribou and calves were und...

The frequency of antlerless female caribou and reindeer in Alaska

The presence or absence of antlers in female caribou and reindeer may reflect genetic or nutritional effects. We classified antler status of female caribou of the Alaska Central Arctic Herd in 1994, 1995, and 2002, and female reindeer in two captive Alaskan herds in 1994. Of 3091 female caribou classified during three years, 152 (4.9%) were antlerless. Frequency of antlerless females in the Central Arctic Herd was similar to that of other Alaskan caribou herds. There were no antlerless females among 231 classified captive reindeer. We compared the frequency of antlerless females in the Alaskan herds with other herds, and possible nutritional and genetic influences on female antler status are discussed.

Factors Affecting Birth Dates of Sympatric Deer in West-Central Texas

Abstract During a study of fawn mortality, we investigated proximate factors affecting birth dates of sympatric desert mule deer (Odocoileus hemionus eremicus) and white-tailed deer (O. virginianus texanus) in west-central Texas from 2004 to 2006. We treated this aspect of the study as time-to-event survival (i.e., pregnancy to birth) and modeled the process with accelerated failure-time regression. Our best model included effects from 3 hierarchal levels: within-year variation among individuals within species, because older and heavier females gave birth earlier; among-year variation at the population level, because greater rain during the previous prerut and rut periods resulted in earlier birth dates; and a chronic-cohort effect also at the population level, because even after previous effects were accounted for in regression models, deer gave birth later on more intensely grazed ranches. After accounting for mass, age of females as a significant predictor may have indicated a behavioral phenomenon associated with social dominance. We did not find meaningful relationships between birth dates and either offspring sex or rain during gestation. Overall, Kaplan–Meier product-limit estimates indicated that birthing by white-tailed deer peaked on 20 June (90% range = 31 days) and birthing by mule deer peaked on 21 July (90% range = 45 days). We suggest that the 1-month separation between peak birth dates and breeding periods of these sympatric species of deer was partly due to phylogenetic constraint from parent populations and not localized adaptation with selection against hybridization. Prevention of genetic introgression may be a result by coincidence.

Limitations of Thermal Infrared Imaging for Locating Neonatal Deer in Semiarid Shrub Communities

Abstract Neonate capture can be an important part of ungulate research. Systematic grid searching has been the most common method, but it is time consuming and usually requires a large number of people. A variety of methods have been used by wildlife professionals to capture ungulate neonates. We used a Raytheon PalmIR 250 Digital (Raytheon Commercial Infrared, Dallas, Texas) thermal infrared camera during the coolest time of night to search for deer (Odocoileus spp.) neonates in west-central Texas, USA. Using 2 methods (stationary observation and mobile searching), we detected one fawn and captured none. Efficacy of this technology at our study site may have been limited by the lack of a forest canopy and density of shrubs and herbaceous cover on our study site. Ground cover can obscure a bedded fawn, and direct sunlight on bed site habitat can result in false signals. We suggest wildlife professionals consider vegetation parameters, ungulate density, and road quality before purchasing expensive thermal imaging equipment.

Factors limiting productivity of the Central Arctic Caribou Herd of Alaska

Many biotic and abiotic factors can limit productivity and growth of caribou (Rangifer tarandus) herds, but limiting factors typically vary by region. Identifying limiting factors may help to indicate which seasons are of relative importance to a caribou herd and possibly to suggest general life history strategies. Using regression techniques, we found that despite previous suggestions, net productivity of Alaska’s Central Arctic Caribou Herd (CAH) did not respond to early summer forage biomass or summer insect severity from the previous year. Abiotic factors that did have apparent effects on CAH productivity included early fall snow deposition, winter snow condition, and spring snow ablation. To achieve a suitable weight for conception, caribou of the CAH may exhibit a seasonal time-minimizing foraging strategy by moderating weight gain during the warm summer insect season and feeding more intensively during the insect-free weeks before the autumn rut. A long-term trend of the Northern Hemisphere annular mode (NAM) may be linked to anthropogenic climate change and may have negative implications for the future success of the CAH.

Evaluation of Use of Vaginal-Implant Transmitters in Mule Deer (Odocoileus hemionus)

Abstract During two studies of mortality in fawns of desert mule deer (Odocoileus hemionus eremicus) in Crockett County, Texas, and Gila County, Arizona, we recorded rates of retention and problems with vaginal-implant transmitters (VITs). Our objectives were to determine if rates of retention differed between studies, years, timing of insertions, and width of wing of VITs. In Texas, VITs with wings 6.75-cm wide were shed successfully at parturition 73–77% of the time, whereas in Arizona, VITs were shed successfully 43% of the time. Additionally, in Arizona, VITs with 8.20-cm-wide wings were shed successfully 91% of the time. Our data suggested that optimal length of wings of VITs for mule deer may be dependent on locale. When designing a study using VITs, researchers should use the largest wing possible to ensure high rates of retention without physically harming deer.

Differences in Timing of Parturition, Birthing Sites, and Bedding Sites of Fawns in Sympatric Populations of Deer

Abstract Mule deer (Odocoileus hemionus) have been declining throughout the western United States and white-tailed deer (O. virginianus) have remained stable or increased. In areas of sympatry, it is important to understand dynamics between the two species. Crockett County, Texas, provided an area where the two species occurred sympatrically at relatively high densities. In summers 2004–2005, we captured adult deer and fitted them with radiocollars and vaginal-implant transmitters. We monitored vaginal-implant transmitters to record date of parturition, to locate birth sites, and to aid in capture of neonates. We captured 101 neonates (68 mule deer and 33 white-tailed deer). We observed 45 parturition sites and 249 day-time bedding sites of fawns. Parturition in mule deer began ca. 1 month after white-tailed deer. Birth sites of mule deer were at higher elevations and on steeper slopes than those of white-tailed deer. Mule deer gave birth under junipers (Juniperus) more often than did white-tailed deer. Our best model used elevation, height of horizontal hiding cover, type of vegetation, canopy shrub, and an interaction between vegetation type and canopy shrub to differentiate between bedding sites of fawns of mule deer and white-tailed deer. Fawns of mule deer bedded at higher elevations in shorter hiding cover and commonly under junipers, whereas fawns of white-tailed deer commonly bedded under honey mesquite (Prosopis glandulosa) or in herbaceous vegetation. Our data show that fawns partition habitat in a manner similar to adults in this area.