Spatial prey availability and pulsed reproductive tactics: Encounter risk in a canid-ungulate system.

Predation risk is a function of spatiotemporal overlap between predator and prey, as well as behavioural responses during encounters. Dynamic factors (e.g. group size, prey availability and animal movement or state) affect risk, but rarely are integrated in risk assessments. Our work targets a system where predation risk is fundamentally linked to temporal patterns in prey abundance and behaviour. For neonatal ungulate prey, risk is defined within a short temporal window during which the pulse in parturition, increasing movement capacity with age and antipredation tactics have the potential to mediate risk. In our coyote-mule deer (Canis latrans-Odocoileus hemionus) system, leveraging GPS data collected from both predator and prey, we tested expectations of shared enemy and reproductive risk hypotheses. We asked two questions regarding risk: (A) How does primary and alternative prey habitat, predator and prey activity, and reproductive tactics (e.g. birth synchrony and maternal defence) influence the vulnerability of a neonate encountering a predator? (B) How do the same factors affect behaviour by predators relative to the time before and after an encounter? Despite increased selection for mule deer and intensified search behaviour by coyotes during the peak in mule deer parturition, mule deer were afforded protection from predation via predator swamping, experiencing reduced per-capita encounter risk when most neonates were born. Mule deer occupying rabbit habitat (Sylvilagus spp.; coyote's primary prey) experienced the greatest risk of encounter but the availability of rabbit habitat did not affect predator behaviour during encounters. Encounter risk increased in areas with greater availability of mule deer habitat: coyotes shifted their behaviour relative to deer habitat, and the pulse in mule deer parturition and movement of neonatal deer during encounters elicited increased speed and tortuosity by coyotes. In addition to the spatial distribution of prey, temporal patterns in prey availability and animal behavioural state were fundamental in defining risk. Our work reveals the nuanced consequences of pulsed availability on predation risk for alternative prey, whereby responses by predators to sudden resource availability, the lasting effects of diversionary prey and inherent antipredation tactics ultimately dictate risk.

A test of the frost wave hypothesis in a temperate ungulate.

Growing evidence supports the hypothesis that temperate herbivores surf the green wave of emerging plants during spring migration. Despite the importance of autumn migration, few studies have conceptualized resource tracking of temperate herbivores during this critical season. We adapted the frost wave hypothesis (FWH), which posits that animals pace their autumn migration to reduce exposure to snow but increase acquisition of forage. We tested the FWH in a population of mule deer in Wyoming, USA by tracking the autumn migrations of n = 163 mule deer that moved 15-288 km from summer to winter range. Migrating deer experienced similar amounts of snow but 1.4-2.1 times more residual forage than if they had naïve knowledge of when or how fast to migrate. Importantly, deer balanced exposure to snow and forage in a spatial manner. At the fine scale, deer avoided snow near their mountainous summer ranges and became more risk prone to snow near winter range. Aligning with their higher tolerance of snow and lingering behavior to acquire residual forage, deer increased stopover use by 1 ± 1 day (95% CI) day for every 10% of their migration completed. Our findings support the prediction that mule deer pace their autumn migration with the onset of snow and residual forage, but refine the FWH to include movement behavior en route that is spatially dynamic.

Coursing the mottled mosaic: Generalist predators track pulses in availability of neonatal ungulates.

The density and distribution of resources shape animal movement and behavior and have direct implications for population dynamics. Resource availability often is "pulsed" in space and time, and individuals should cue in on resource pulses when the energetic gain of doing so exceeds that of stable resources. Birth pulses of prey represent a profitable but ephemeral resource and should thereby result in shifting functional responses by predators. We evaluated movements and resource selection of coyotes (Canis latrans) across a gradient of reproductive stages ranging from late gestation to peak lactation of female mule deer (Odocoileus hemionus) in southwest Wyoming, USA, to test whether coyotes exhibited shifts in selection and movement behavior relative to the availability and vulnerability of neonatal mule deer. We expected coyotes to track pulses in availability of neonatal mule deer, and such behavior would be represented by shifts in resource selection and search behavior of coyotes that would be strongest during peak parturition of mule deer. Coyotes selected areas of high relative probability of use by female mule deer and did so most strongly during peak parturition. Furthermore, searching behavior of coyotes intensified during pulses of availability of deer neonates. Our findings support the notion that coyotes exploit pulses of neonatal deer, presumably as an attempt to capitalize on a vulnerable, energy-rich resource. Our work quantifies the behavioral mechanisms by which coyotes consume ungulate neonates and provides one of the first examples of a mammalian predator-prey system centered on a pulsed resource.

Risky business: How an herbivore navigates spatiotemporal aspects of risk from competitors and predators.

Understanding factors that influence animal behavior is central to ecology. Basic principles of animal ecology imply that individuals should seek to maximize survival and reproduction, which means carefully weighing risk against reward. Decisions become increasingly complex and constrained, however, when risk is spatiotemporally variable. We advance a growing body of work in predator-prey behavior by evaluating novel questions where a prey species is confronted with multiple predators and a potential competitor. We tested how fine-scale behavior of female mule deer (Odocoileus hemionus) during the reproductive season shifted depending upon spatial and temporal variation in risk from predators and a potential competitor. We expected female deer to avoid areas of high risk when movement activity of predators and a competitor were high. We used GPS data collected from 76 adult female mule deer, 35 adult female elk, 33 adult coyotes, and six adult mountain lions. Counter to our expectations, female deer exhibited selection for multiple risk factors, however, selection for risk was dampened by the exposure to risk within home ranges of female deer, producing a functional response in habitat selection. Furthermore, temporal variation in movement activity of predators and elk across the diel cycle did not result in a shift in movement activity by female deer. Instead, the average level of risk within their home range was the predominant factor modulating the response to risk by female deer. Our results counter prevailing hypotheses of how large herbivores navigate risky landscapes and emphasize the importance of accounting for the local environment when identifying effects of risk on animal behavior. Moreover, our findings highlight additional behavioral mechanisms used by large herbivores to mitigate multiple sources of predation and potential competitive interactions.

Cats and dogs: A mesopredator navigating risk and reward provisioned by an apex predator.

Successfully perceiving risk and reward is fundamental to the fitness of an animal, and can be achieved through a variety of perception tactics. For example, mesopredators may "directly" perceive risk by visually observing apex predators, or may "indirectly" perceive risk by observing habitats used by predators. Direct assessments should more accurately characterize the arrangement of risk and reward; however, indirect assessments are used more frequently in studies concerning the response of GPS-marked animals to spatiotemporally variable sources of risk and reward. We investigated the response of a mesopredator to the presence of risk and reward created by an apex predator, where risk and reward likely vary in relative perceptibility (i.e., degree of being perceptible). First, we tested whether coyotes (Canis latrans) use direct or indirect assessments to navigate the presence of mountain lions (Puma concolor; risk) and kills made by mountain lions (reward) in an area where coyotes were a common prey item for mountain lions. Second, we assessed the behavioral response of coyotes to direct encounters with mountain lions. Third, we evaluated spatiotemporal use of carrion by coyotes at kills made by mountain lions. Indirect assessments generally outperformed direct assessments when integrating analyses into a unified framework; nevertheless, our ability to detect direct perception in navigating to mountain lion kills was likely restricted by scale and sampling limitations (e.g., collar fix rates, unsampled kill sites). Rather than responding to the risk of direct encounters with mountain lions, coyotes facilitated encounters by increasing their movement rate, and engaged in risky behavior by scavenging at mountain lion kills. Coyotes appear to mitigate risk by using indirect perception to avoid mountain lions. Our predator-predator interactions and insights are nuanced and counter to the conventional predator-prey systems that have generated much of the predation risk literature.