Migratory behavior in ungulates has declined globally and understanding the causative factors (environmental change vs. human mediated) is needed to formulate effective management strategies. In the Jackson elk herd of northwest Wyoming, demographic differences between summer elk (Cervus elaphus) population segments have led to changes in migratory patterns over a 35-year time period. The proportion of short-distance migrants (SDM) has increased and the proportion of long-distance migrants (LDM) has concurrently declined. The probability of winter-captured elk on the National Elk Refuge being LDM decreased from 0.99 (95% CI ¼ 0.97-1.00) to 0.59 (95% CI ¼ 0.47-0.70) from 1978 to 2012. We tested 4 hypotheses that could contribute toward the decline in the LDM segment: behavioral switching from LDM to SDM, differential survival, harvest availability, and calf recruitment. Switching rates from LDM to SDM were very low (0.2% each elk-year). Survival rates were similar between LDM and SDM, although harvest availability was relatively low for SDM that tended to use areas close to human development during the hunting season. Average summer calf/cow ratios of LDM declined from 42 to 23 calves per 100 cows from 1978 -2012 . Further, during 2006 -2012, LDM summer calf/cow ratios were less than half of SDM (23 vs. 47 calves per 100 cows). Our data suggest recruitment is the driving factor behind the declining proportion of LDM in this region. Effectiveness of altering harvest management strategies to conserve the LDM portion of the Jackson elk herd may be limited. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

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Patterns of male reproductive allocation provide insight into life-history characteristics. The trade-offs associated with resource and female group defence are well-defined. However, less is understood about trade-offs in species that practise scramble-competition polygyny, where successful strategies may favour competitive mate-searching rather than contest competition and fighting. White-tailed deer (Odocoileus virginianus) practise scramble-competition polygyny where solitary males search for and assess receptivity of females scattered across the landscape. Physically mature males are expected to do most of the breeding because of the high energetic costs of reproduction and high social status. However, young males may collectively sire one-third of offspring. To gain a better understanding of trade-offs associated with scramble-competition polygyny, we quantified metrics associated with reproductive effort and success. We quantified changes in body mass of harvested males, energetic costs of locomotion based on movements of GPS radiocollared males and timing of reproduction via temporal genetic parentage assignments. Young males (1.5 and 2.5 years old) sired offspring, but their mating success was mainly limited to peak rut, when most females were in oestrus. Furthermore, multiple paternity was common, indicating opportunistic reproduction. Reproductive effort, indexed by body mass loss, was highest in prime-age males (5.5-6.5 years old). Surprisingly, young and postprime males also exhibited significant body mass loss, indicative of investment in reproductive effort. Movement rates increased twofold to fourfold during rut as a function of mate search activities, but cost of locomotion would cause only about one-third of observed body mass loss. Because males are capital breeders, we infer most of body mass loss is due to reduced foraging. In scramble-competition polygyny, the repeated location of potential mates and assessment of their oestrous status appear to be important constituents of male mating strategies. Therefore, mating success may be influenced by time management and spatial memory, and not based solely on social dominance. Thus, reproductive effort should be greater for individuals capable of reducing time foraging. For those that cannot, opportunistic mating opportunities may arise when operative adult sex ratios are low. Our analyses reveal valuable insight into the trade-offs associated with scramble-competition polygyny.

White-tailed deer are a culturally and economically important game species in North America, especially in South Texas. The recent discovery of chronic wasting disease (CWD) in captive deer facilities in Texas has increased concern about the potential emergence of CWD in free-ranging deer. The concern is exacerbated because much of the South Texas region is a semi-arid environment with variable rainfall, where precipitation is strongly correlated with fawn recruitment. Further, the marginally productive rangelands, in combination with erratic fawn recruitment, results in populations that are frequently density-independent, and thus sensitive to additive mortality. It is unknown how a deer population in semi-arid regions would respond to the presence of CWD. We used long-term empirical datasets from a lightly harvested (2% annual harvest) population in conjunction with 3 prevalence growth rates from CWD afflicted areas (0.26%, 0.83%, and 2.3% increases per year) via a multi-stage partially deterministic model to simulate a deer population for 25 years under four scenarios: 1) without CWD and without harvest, 2) with CWD and without harvest, 3) with CWD and male harvest only, and 4) with CWD and harvest of both sexes. The modeled populations without CWD and without harvest averaged a 1.43% annual increase over 25 years; incorporation of 2% annual harvest of both sexes resulted in a stable population. The model with slowest CWD prevalence rate growth (0.26% annually) without harvest resulted in stable populations but the addition of 1% harvest resulted in population declines. Further, the male age structure in CWD models became skewed to younger age classes. We incorporated fawn:doe ratios from three CWD afflicted areas in Wisconsin and Wyoming into the model with 0.26% annual increase in prevalence and populations did not begin to decline until ~10%, ~16%, and ~26% of deer were harvested annually. Deer populations in variable environments rely on high adult survivorship to buffer the low and erratic fawn recruitment rates. The increase in additive mortality rates for adults via CWD negatively impacted simulated population trends to the extent that hunter opportunity would be greatly reduced. Our results improve understanding of the potential influences of CWD on deer populations in semi-arid environments with implications for deer managers, disease ecologists, and policy makers.

Antler traits are both genetically determined and environmentally influenced. However, the degree to which environmental factors affect antler expression has rarely been quantified. We captured 30 to 150 male whitetailed deer (Odocoileus virginianus) annually at 7 South Texas sites during 1985 to 2009 to determine repeatability of antler traits from a semiarid environment with variable rainfall. Repeatability is defined as the intraclass correlation between repeated measures of the same trait over time. Repeatability was moderate to high (0.42-0.82) for all antler traits. Overall, number of antler points had the lowest repeatability, whereas inside spread of main beams and length of main beams had the highest repeatability. Repeatability of total antler score and number of antler points from sites with variable rainfall was 16% and 24% lower than sites with consistent rainfall, respectively. Sites with variable rainfall had 13-18% higher repeatability when enhanced nutrition was available. Studies of cervids reveal a tendency for lower repeatability of antler traits as the environmental conditions become more variable. The association between repeatability and variable environmental conditions illustrates the magnitude of environmental effects and supports the role of antlers as an honest advertisement of individual condition or quality. Our results help to understand potential of microevolution in antlers and have implications for sexual selection and harvest management.

Aerial surveys are an efficient technique for counting animals over large geographic areas such as rangelands. In southwestern rangelands, aerial surveys are routinely conducted for ungulates, with the implicit understanding that abundance estimates represent an undercount. Distance sampling can correct for visibility bias, but assumes perfect detection on the survey line, a condition often violated in aerial surveys of ungulates. The incorporation of mark‐resight methods into the distance‐sampling framework, termed mark‐recapture distance sampling (MRDS), corrects for both visibility bias and imperfect detection on the survey line. However, the use of MRDS introduces logistical and technical constraints that may not be practical for aerial surveys. We conducted aerial surveys of ungulates on rangelands in south Texas, USA, to evaluate the feasibility and performance of MRDS relative to conventional distance sampling (CDS) and multiple covariate distance sampling (MCDS). We conducted surveys prior to and after leaf‐fall in 2013–2015 to test the hypothesis that distance sampling corrected for changes in visibility bias. We surveyed white‐tailed deer (Odocoileus virginianus), nilgai (Boselaphus tragocamelus), collared peccary (Pecari tajacu), and feral swine (Sus scrofa) on 4 sites. Each site was surveyed seasonally for 2 years; twice both prior to (Nov) and after leaf‐fall (Feb). Probability of detection on survey lines for each species was high (range = 0.82–0.97) and the average for each species was similar between seasons (0.89 and 0.92 during pre and post leaf‐fall, respectively). The MRDS density estimates often were only ~10% greater than CDS and MCDS estimates; all population estimates had overlapping 95% confidence intervals. Further, CDS and MCDS estimates were similar indicating that measured covariates (seat position, vegetation type, and cluster size) contributed little towards detection probabilities. Despite similar average probability of detection for all species before and after leaf‐fall (0.47 and 0.51, respectively), deer and nilgai population estimates were 22–59% lower during fall surveys than winter surveys. The discrepancy between consistent probability of detections with different population estimates suggests that availability bias, which cannot be addressed with distance sampling, was an issue. Overall, the MRDS technique addressed imperfect detection on the survey line and generated probabilities of detection in the survey area consistent with previous studies done in Texas. However, the extra costs (~US$13,000) and logistical hurdles to preserve observer independence for a small increase in precision of population estimates may not be justifiable. © 2020 The Wildlife Society.