Habitat use and spatio‐temporal interactions of mule and white‐tailed deer in an area of sympatry in NE Washington

Permanent daylight saving time would reduce deer-vehicle collisions

Overlap between wildlife and human activity is key to causing wildlife-vehicle collisions, a globally pervasive and growing source of wildlife mortality.^1,2 Policies regarding clock time often involve abrupt seasonal shifts in human activity, potentially influencing rates of human-wildlife conflict. Here, we harness the biannual shift between standard and daylight saving time as a natural experiment to reveal how the timing of human activity influences deer-vehicle collisions. Based on 1,012,465 deer-vehicle collisions and 96 million hourly traffic observations across the United States, we show that collisions are 14 times more frequent 2 hours after sunset than before sunset, highlighting the importance of traffic during dark hours as a key determinant of deer-vehicle collision risk. The switch from daylight saving to standard time in autumn causes peak traffic volumes to shift from before sunset to after sunset, leading to a 16% spike in deer-vehicle collisions. By reducing traffic after dark, our model predicts that year-round daylight saving time would prevent 36,550 deer (Odocoileus sp.) deaths, 33 human deaths, 2,054 human injuries, and US$1.19 billion in collision costs annually. In contrast, permanent standard time is predicted to increase collisions by an even larger magnitude, incurring an additional US$2.39 billion in costs. By targeting the temporal dimension of wildlife-vehicle collisions, strategies such as year-round daylight saving time that reduce traffic during dark hours, especially during the breeding season of abundant ungulates, would yield substantial benefits for wildlife conservation and reduce the social and economic costs of deer-vehicle collisions.

How did the deer cross the fence: An evaluation of wildlife-friendlier fence modifications to facilitate deer movement

Fences are a common feature throughout the landscape of North America’s Great Plains region. Knowledge surrounding the harmful implication that fences have on the movement of wildlife, specifically ungulates, is expanding. Across the region, it is accepted that there is a need to mitigate the impacts of barbed wire fencing and that “wildlife-friendlier” fence designs are emerging as a practical tool to meet these goals. Here we evaluate the response of sympatric deer species to the implementation of two fence modifications, fastening the top two wires together using clips and the installation of polyvinyl chloride (PVC) pipe to encompass the top two wires. We also aim to determine the optimal top wire height to allow for successful crossing by deer, with the goal to provide a more robust understanding of effective wildlife-friendlier fence standards. We used remote trail cameras to capture crossing events and recorded responses for mule deer (Odocoileus hemionus) and white-tailed deer (Odocoileus virginianus). Using generalized linear mixed modelling, we tested the influence modifications had on crossing success and decisions prior to and after the modifications were installed compared to control sites. We found that these modifications had little impact on deer crossing behavior. We determined that wire height had the greatest impact on the permeability of fences, but that deer permeability was strongly influenced by species and sex. We found that the current maximum recommended top wire height of 102 cm (40 inches) is adequate to allow individuals of both deer species to cross over the fence, with the exception of female mule deer. Our results also indicate as the top wire height reaches 110 cm (43 inches) or higher, that the probability of successfully jumping over the fence dramatically drops off, with the exception for male mule deer. We recommend the installation of clips as a cost-effective method to lower top wire height and PVC pipe to improve fence visibility and potentially reduce entanglement events, all while effectively keeping livestock in intended pastures.

A model-based estimate of winter distribution and abundance of white-tailed deer in the Adirondack Park

In the Adirondack Park region of northern New York, USA, white-tailed deer (Odocoileus virginianus) and moose (Alces alces) co-occur along a temperate-boreal forest ecotone. In this region, moose exist as a small and vulnerable low-density population and over-browsing by white-tailed deer is known to reduce regeneration, sustainability, and health of forests. Here, we assess the distribution and abundance of white-tailed deer at a broad spatial scale relevant for deer and moose management in northern New York. We used density surface modeling (DSM) under a conventional distance sampling framework, tied to a winter aerial survey, to create a spatially explicit estimate of white-tailed deer abundance and density across a vast, northern forest region. We estimated 16,352 white-tailed deer (95% CI 11,762–22,734) throughout the Adirondack Park with local density ranging between 0.00–5.73 deer/km². Most of the Adirondack Park (91.2%) supported white-tailed deer densities of ≤2 individuals/km². White-tailed deer density increased with increasing proximity to anthropogenic land cover such as timber cuts, roads, and agriculture and decreased in areas with increasing elevation and days with snow cover. We conclude that climate change will be more favorable for white-tailed deer than for moose because milder winters and increased growing seasons will likely have a pronounced influence on deer abundance and distribution across the Adirondack Park. Therefore, identifying specific environmental conditions facilitating the expansion of white-tailed deer into areas with low-density moose populations can assist managers in anticipating potential changes in ungulate distribution and abundance and to develop appropriate management actions to mitigate negative consequences such as disease spread and increased competition for limiting resources.

Co-occurrence models fail to infer underlying patterns of avoidance and aggregation when closure is violated

Advances in multi‐species monitoring have prompted an increase in the use of multi‐species occupancy analyses to assess patterns of co‐occurrence among species, even when data were collected at scales likely violating the assumption that sites were closed to changes in the occupancy state for the target species. Violating the closure assumption may lead to erroneous conclusions related to patterns of co‐occurrence among species. Occurrence for two hypothetical species was simulated under patterns of avoidance, aggregation, or independence, when the closure assumption was either met or not. Simulated populations were sampled at two levels (N = 250 or 100 sites) and two scales of temporal resolution for surveys. Sample data were analyzed with conditional two‐species occupancy models, and performance was assessed based on the proportion of simulations recovering the true pattern of co‐occurrence. Estimates of occupancy were unbiased when closure was met, but biased when closure violations occurred; bias increased when sample size was small and encounter histories were collapsed to a large‐scale temporal resolution. When closure was met and patterns of avoidance and aggregation were simulated, conditional two‐species models tended to correctly find support for non‐independence, and estimated species interaction factors (SIF) aligned with predicted values. By contrast, when closure was violated, models tended to incorrectly infer a pattern of independence and power to detect simulated patterns of avoidance or aggregation that decreased with smaller sample size. Results suggest that when the closure assumption is violated, co‐occurrence models often fail to detect underlying patterns of avoidance or aggregation, and incorrectly identify a pattern of independence among species, which could have negative consequences for our understanding of species interactions and conservation efforts. Thus, when closure is violated, inferred patterns of independence from multi‐species occupancy should be interpreted cautiously, and evidence of avoidance or aggregation is likely a conservative estimate of true pattern or interaction.

Mule deer do more with less: comparing their nutritional requirements and tolerances with white-tailed deer

Congeneric species often share ecological niche space resulting in competitive interactions that either limit co-occurrence or lead to niche partitioning. Differences in fundamental nutritional niches mediated through character displacement or isolation during evolution are potential mechanisms that could explain overlapping distribution patterns of congenerics. We directly compared nutritional requirements and tolerances that influence the fundamental niche of mule (Odocoileus hemionus) and white-tailed deer (O. virginianus), which occur in allopatry and sympatry in similar realized ecological niches across their ranges in North America. Digestible energy and protein requirements and tolerances for plant fiber and plant secondary metabolites (PSMs) of both deer species were quantified using in vivo digestion and intake tolerance trials with six diets ranging in content of fiber, protein, and PSMs using tractable deer raised under identical conditions in captivity. We found that compared with white-tailed deer, mule deer required 54% less digestible protein and 21% less digestible energy intake per day to maintain body mass and nitrogen balance. In addition, they had higher fiber, energy, and dry matter digestibility and produced glucuronic acid (a byproduct of PSM detoxification) at a slower rate when consuming the monoterpene α-pinene. The mule deers’ enhanced physiological abilities to cope with low-quality, chemically defended forages relative to white-tailed deer might minimize potential competitive interactions in shared landscapes and provide a modest advantage to mule deer in habitats dominated by low-quality forages.