About

Aaron J. Wirsing is a professor at the University of Washington School of Environmental and Forest Sciences, with research focusing on wildlife science. His academic background includes a Bachelor of Arts in Biology from Bowdoin College, a Master of Science in Wildlife Resources from the University of Idaho, and a Ph.D. in Biological Sciences from Simon Fraser University. His current sponsored projects include studies on snow leopard ecology in Kyrgyzstan, interactions between wolves and cougars in Washington, and the effects of anti-predator behavior on predator-prey dynamics. Wirsing's research contributions encompass understanding predator-prey interactions, ecological roles of large carnivores, and the behavioral responses of wildlife to predation risk. His work has been published in various scientific journals, addressing topics such as shark ecology, ungulate responses to predation, and the ecological importance of sea cows. He is involved in teaching courses related to wildlife biology and conservation and actively contributes to advancing ecological research through sponsored projects and scholarly publications.

Research topics

• Geography

Selected publications

• FIU-SharkFishCoral-FrenchPoly: Analysis code for top-down and bottom-up forcing on French Polynesian coral reefs

  Zenodo (CERN European Organization for Nuclear Research) · 2026-04-28

  otherOpen access

  R analysis pipeline for the manuscript "Top-down and bottom-up forcing on coral reefs changes with habitat-specific predator abundance" (Dedman et al. 2026). Provides scripts to reproduce all figures and statistical results: data preparation from benthic UVC and BRUV surveys; boosted regression tree (BRT) models of fish biomass and benthic cover; structural causal modelling using Bayesian regression (brms) with cubic shrinkage splines; directed acyclic graph (DAG) consistency testing and visualisation. Tested on R 4.3+; package versions pinned via renv.

  PublisherDOI

• FIU-SharkFishCoral-FrenchPoly: Analysis code for top-down and bottom-up forcing on French Polynesian coral reefs

  Open MIND · 2026-04-28

  otherOpen access

  R analysis pipeline for the manuscript "Top-down and bottom-up forcing on coral reefs changes with habitat-specific predator abundance" (Dedman et al. 2026). Provides scripts to reproduce all figures and statistical results: data preparation from benthic UVC and BRUV surveys; boosted regression tree (BRT) models of fish biomass and benthic cover; structural causal modelling using Bayesian regression (brms) with cubic shrinkage splines; directed acyclic graph (DAG) consistency testing and visualisation. Tested on R 4.3+; package versions pinned via renv.

  PublisherDOI

• The Talion law “tooth for a tooth”: self-defense as a motivation for shark bites on human aggressors

  Frontiers in Conservation Science · 2025-04-25

  articleOpen accessSenior author

  The concept of “self-defense,” based on aggression by one individual responding to an initial aggression by another, has been observed in several animal taxa such as birds and terrestrial mammals but never documented in detail in sharks. Based on a multi-decade study of the characteristics of shark bites on humans in French Polynesia Eastern-South Pacific, we show that certain human activities at sea, such as fishing and particularly underwater spearfishing and the management of passive fish traps, are associated with this type of bite. Following an initial agonistic behavior by a human on a shark, a pattern of self-defense bites ensues, characterized by immediate aggression in return. It is perpetrated without proportionality, often superficial with minimal tearing of flesh, and rarely fatal, except in special circumstances. During these interactions, the shark will sometimes respond to the initial anthropogenic stimulus with repeated bites. The motivation for these defensive bites can be distinguished from other drivers, such as the predation motivation on humans, which involves heavy loss of tissue. In the case of antipredation or fear motivation, when a shark anticipates a potential human aggression before it occurs, the attack is preceded by a characteristic agonistic behavior that is not present in the case of self-defense. The existence of this behavior cautions that attacks on sharks have the potential to trigger retaliatory bites and that untrained persons should never attempt to come to the rescue of a distressed shark, which may bite indiscriminately. Finally, we suggest that the media, which often sensationalizes these types of self-defense bites as attacks, could help to improve attitudes toward sharks and their conservation by more objectively reporting the culpability of humans in triggering them.

  PublisherOA PDFDOI

• Navigating the risks and rewards of scavenging in multipredator, human‐impacted landscapes

  Ecology · 2025-05-01 · 2 citations

  articleOpen access

  Large carnivores can influence smaller scavengers through both positive and negative interactions (e.g., carrion provisioning and intraguild killing) and ultimately shape scavenging efficiency. However, we know little about this trade-off in anthropogenic landscapes where humans kill carnivores and provide carrion subsidies. In the context of wolf (Canis lupus) recolonization of human-impacted landscapes in Washington, USA, we investigated how sources of ungulate mortality (wolves, cougars [Puma concolor], and vehicles) shape scavenging efficiency, community-wide carcass visitations, and the strategies used by scavengers to navigate risk-reward trade-offs. Cougar and wolf kills mostly occurred in areas with low-to-moderate human influence, whereas roadkill typically occurred in areas with high human impact. Wolves consumed their kills most rapidly (median <4.7 days), providing fewer scavenging opportunities than cougar- and vehicle-killed ungulates, which persisted longer (median = 8.9 and 12 days, respectively). Roadkill primarily attracted avian scavengers, whereas mammalian scavengers used roadkill to a lesser degree and did so by shifting to more nocturnal foraging. The absence in winter of turkey vultures (Cathartes aura) and black bears (Ursus americanus), which are obligate and apex scavengers, respectively, coincided with a seasonal increase in scavenging by most other species. The two mammalian mesocarnivores exhibited divergent strategies: Coyotes (Canis latrans) frequently scavenged but usually for short durations and with heightened vigilance at predator kills, whereas bobcats (Lynx rufus) visited carcasses less frequently but fed for longer durations and displayed low vigilance while scavenging. These results suggest a hierarchical decision-making process whereby scavengers first choose whether to forage at a carcass before fine-tuning foraging duration, using temporal refugia, or increasing vigilance. Predator recovery in human-dominated landscapes therefore adds complexity to the spatiotemporal landscape of risks and rewards, and outcomes for scavengers will likely depend on their propensity to scavenge and vulnerability to humans and large predators.

  PublisherOA PDFDOI

• Foraging tactics and success rates of brown bears preying on sockeye salmon in small streams

  Journal of Mammalogy · 2025-06-12 · 1 citations

  article

  Abstract Studies of foraging where focal animals are easily observed may miss common behaviors expressed under more cryptic conditions. For example, much of what is known about brown bears (Ursus arctos) foraging on Pacific salmon (Oncorhynchus spp.) comes from a few anomalous locations where bears congregate, leaving open the question of how bears exploit salmon in the small streams where most predation occurs. Here, we used motion-activated video recordings to study the use and success of foraging tactics of Alaskan brown bears preying on Sockeye Salmon (O. nerka) in 6 small streams over 3 summers (2016, 2021, 2022). We first identified 8 tactics from 387 independent foraging bouts and used multinomial models to explore drivers of their use (bear age and sex, salmon abundance, stream, diel period, and year). We then used generalized linear models to examine factors influencing their success in capturing salmon (those identified above plus foraging tactic, month, and interactions between foraging tactic and salmon abundance, and foraging tactic and age). Cubs were far more likely to use sporadic foraging—a haphazard approach characterized by low success and high energy expenditure—than were adults, suggesting that this tactic may reflect inexperience. Tactics also varied with diel period and year. Foraging success was affected by tactic; notably, bears engaged in mixed and sporadic foraging were far less likely to catch a salmon than those using active tactics, whereas bears foraging passively were far more likely to catch a salmon than those foraging actively. Foraging success also varied among years but was not related to salmon abundance. These findings: (i) showcase the diverse approaches brown bears use to exploit salmon in small streams; (ii) add to our understanding of the ontogeny and success rates of foraging behaviors in habitats where most predation on salmon occurs; and (iii) highlight the utility of video recording for overcoming challenges to the direct observation of bear behavior.

  PublisherDOI

• Apex predators exploit advantageous snow conditions across hunting modes

  Journal of Animal Ecology · 2025-10-27

  articleOpen access

  Abstract Apex predators balance functional traits, habitat features, and prey distribution to maximize hunting efficiency. As components of habitat such as snow cover are altered by climate change, functional traits may prove more or less effective given new environmental conditions, with ecosystem‐wide impacts as a result of changing predator‐prey interactions. Hunting mode is one such functional trait that shapes which environments are best for catching prey. Coursing large carnivores may exploit snow conditions that offer movement advantages, with long chase sequences maximizing their superior mobility over large‐bodied ungulate prey that typically sink deeper into snow. However, comparatively little is known about whether stalking predators utilize snow similarly, despite similar theoretical movement advantages over prey. In this study, we examined the effects of snow on two sympatric predators with different hunting strategies: cougars ( Puma concolor ; stalking predators) and wolves ( Canis lupus ; coursing predators). We coupled a physically based snow model with kill site investigations and telemetry data from 50 cougars, 14 wolves, 142 mule deer ( Odocoileus hemionus ), and 90 white‐tailed deer ( O. virginianus ) collected from 2017 to 2021 in Washington state, USA. We first created winter deer distribution models for each year to control for expected prey density. We then generated step selection functions for cougars and wolves using this deer index, snow properties, and other landscape characteristics hypothesized to influence the hunting process. The interaction between snow depth and density shaped both predators’ movements and was an unexpectedly strong driver of cougar winter movements and kill site distribution. Wolves weakly selected for shallow (&lt;35 cm), low density (&lt;200 kg/m 3 ) snow, and avoided deeper snow unless sufficiently dense (&gt;350 kg/m 3 ). Cougars selected for very dense (&gt;400 kg/m 3 ), moderate‐depth (&lt;50 cm) snow and avoided deep snow. Snow depth and density had similar effects on cougar kill site selection ( n = 389 known and probable cougar kills; insufficient sample size for wolves). Our results indicate that snow is a critical component of large carnivore movements regardless of hunting mode. In a warming climate, the knock‐on effects of a diminishing snowpack may reduce the hunting success of multiple large carnivore species, consequently altering predator–prey dynamics with cascading ecosystem‐wide effects.

  PublisherOA PDFDOI

• Metabarcoding reveals striking dietary variation in a reintroduced mesocarnivore

  Journal of Mammalogy · 2025-02-18 · 8 citations

  articleOpen access

  Abstract Carnivore populations are often limited by prey availability, so knowledge of their foraging ecology is required for successful recovery efforts. Limited availability of energy-efficient, or optimal, prey can be a key determinant of the conservation status of mesocarnivores—thus investigating diet habits during reintroduction efforts can provide insights into the trajectory of a reestablishing population. The reintroduction of fishers (Pekania pennanti) in Washington state, United States, offers an opportunity to assess diet variation across reintroduction areas using high-resolution DNA metabarcoding methods. We assessed Fisher diet in 2 reintroduction sites in the Cascade Mountains of Washington (the South Cascades and the North Cascades) where fishers performed differently across multiple metrics used to measure initial reintroduction success. We had the rare opportunity to test correlations between metabarcoding relative read abundance and prey biomass consumption while fishers were fed a known diet while in captivity. We found a moderately positive, though highly variable, correlation (r = 0.47) between approximate biomass consumption of food items and relative read abundance within individual diet samples; however, we detected a strong, though statistically insignificant, correlation between relative read abundance and prey biomass when looking at the relative importance of prey groups in aggregated diet profiles (r = 0.72). We collected 300 Fisher scats and gastrointestinal tracts using telemetry and scat detection dog teams to characterize diet profiles. We found strong, positive correlations between relative read abundance and frequency of occurrence metabarcoding summaries. Hares and rabbits (Lepus americanus and Sylvilagus floridanus) were the most prevalent prey in both populations (North Cascades = 17%, South Cascades = 68%), but there were significant compositional differences between diets of the reintroduced populations. South Cascades fishers had limited prey diversity (n = 19 taxa), whereas 71 taxa were represented in the North Cascades Fisher diet. The diet composition of fishers in the South Cascades was akin to populations in the central and eastern United States, where range expansions are facilitated by access to optimally sized (&amp;gt;250 g) prey. In contrast, the diverse diet of North Cascades fishers was more similar to populations at the southernmost extent of their range (Oregon and California), where optimally sized prey is scarce and population recovery is stunted. The surprisingly high levels of dietary variation among adjacent reintroduction sites highlight the utility of diet studies in evaluating whether translocated populations are obtaining adequate resources to support population establishment and thus informing subsequent management interventions.

  PublisherOA PDFDOI

• Residential development reduces black bear (<i>Ursus americanus</i>) opportunity to scavenge cougar (<i>Puma concolor</i>) killed prey

  Ecology · 2025-02-01 · 1 citations

  articleOpen accessSenior author

  Large carnivores commonly scavenge on kills made by other species, but if and how this phenomenon is influenced by urbanization remains unclear. To address this knowledge deficit, we investigated whether housing density, along with demographic and environmental covariates, impacted the probability of American black bear (Ursus americanus) occurrence at cougar (Puma concolor) killed prey along the wildland-urban gradient of western Washington, USA. Under the refuge hypothesis, which stipulates that residential development reduces opportunities for black bears to visit cougar prey carcasses by (1) altering cougar kill composition and/or (2) drawing black bears to human subsidies, we expected the probability of bear presence at cougar kills to decline as housing density increased. Alternatively, under the pileup hypothesis whereby reduced green space drives a greater overlap and thus more frequent interactions among carnivores, we predicted that bear presence at cougar kills would increase with housing density. Occupancy models derived from forensic and remote camera evidence of bear visitation to carcasses at kill sites identified from 12 GPS-collared cougars indicated that the probability of bear presence at kill sites decreased when cougars foraged on small-bodied prey, increased in summer compared with autumn, and declined with increasing housing density. Indeed, the top model indicated a multiplicative decrease of 500 in the odds of black bear carcass visitation for every additional house per hectare on the landscape, supporting the refuge hypothesis. These results suggest that residential development has the potential to alter intraguild relationships among large carnivores, even at modest levels where robust carnivore populations persist on the landscape, and may alter scavenger dynamics at carcasses where black bear presence is virtually eliminated.

  PublisherOA PDFDOI

• Predator–prey space use and landscape features influence movement behaviors in a large‐mammal community

  Ecology · 2024-10-14 · 5 citations

  articleOpen access

  Predator hunting strategies, such as stalking versus coursing behaviors, are hypothesized to influence antipredator behaviors of prey and can describe the movement behaviors of predators themselves. Predators and prey may alter their movement in relation to predator hunting modes, yet few studies have evaluated how these strategies influence movement behaviors of free-ranging animals in a multiple-predator, multiple-prey system. We fit hidden Markov models (HMM) with movement data derived from >400 GPS-collared ungulates and large predators in eastern Washington, USA. We used these models to test our hypotheses that stalking (cougars [Puma concolor]) and coursing (gray wolves [Canis lupus]) predators would exhibit different broad-scale movement behaviors consistent with their respective hunting strategies in areas that increased the likelihood of encountering or capturing ungulate prey (e.g., habitats selected by deer [Odocoileus spp.]). Similarly, we expected that broadscale movement behaviors of prey would change in response to background levels of predation risk associated with each predator's hunting strategy. We found that predators and ungulate prey adjusted their broadscale movements in response to one another's long-term patterns of habitat selection but not based on differences in predator-hunting strategies. Predators changed their movement behaviors based on the type of prey, whereas ungulates generally reduced movement in areas associated with large predators, regardless of the predator's hunting strategy. Both predator and prey movements varied in response to landscape features but not necessarily based on habitat that would facilitate specific hunting behaviors. Our results suggest that predators and prey adjust their movements at broad temporal scales in relation to long-term patterns of risk and resource distributions, potentially influencing their encounter rates with one another at finer spatiotemporal scales. Habitat features further influenced changes in movement, resulting in a complex combination of movement behaviors in multiple-predator, multiple-prey systems.

  PublisherOA PDFDOI

• White‐tailed deer population dynamics in a multipredator landscape shaped by humans

  Ecological Applications · 2024-06-18 · 9 citations

  articleOpen access

  Large terrestrial mammals increasingly rely on human-modified landscapes as anthropogenic footprints expand. Land management activities such as timber harvest, agriculture, and roads can influence prey population dynamics by altering forage resources and predation risk via changes in habitat, but these effects are not well understood in regions with diverse and changing predator guilds. In northeastern Washington state, USA, white-tailed deer (Odocoileus virginianus) are vulnerable to multiple carnivores, including recently returned gray wolves (Canis lupus), within a highly human-modified landscape. To understand the factors governing predator-prey dynamics in a human context, we radio-collared 280 white-tailed deer, 33 bobcats (Lynx rufus), 50 cougars (Puma concolor), 28 coyotes (C. latrans), and 14 wolves between 2016 and 2021. We first estimated deer vital rates and used a stage-structured matrix model to estimate their population growth rate. During the study, we observed a stable to declining deer population (lambda = 0.97, 95% confidence interval: 0.88, 1.05), with 74% of Monte Carlo simulations indicating population decrease and 26% of simulations indicating population increase. We then fit Cox proportional hazard models to evaluate how predator exposure, use of human-modified landscapes, and winter severity influenced deer survival and used these relationships to evaluate impacts on overall population growth. We found that the population growth rate was dually influenced by a negative direct effect of apex predators and a positive effect of timber harvest and agricultural areas. Cougars had a stronger effect on deer population dynamics than wolves, and mesopredators had little influence on the deer population growth rate. Areas of recent timber harvest had 55% more forage biomass than older forests, but horizontal visibility did not differ, suggesting that timber harvest did not influence predation risk. Although proximity to roads did not affect the overall population growth rate, vehicle collisions caused a substantial proportion of deer mortalities, and reducing these collisions could be a win-win for deer and humans. The influence of apex predators and forage indicates a dual limitation by top-down and bottom-up factors in this highly human-modified system, suggesting that a reduction in apex predators would intensify density-dependent regulation of the deer population owing to limited forage availability.

  PublisherOA PDFDOI

Recent grants

• Collaborative Research: Does Anti-predator Behavior Modify Indirect Effects of Top Predators?

  NSF · $796k · 2012–2018

Frequent coauthors

• Michael R. Heithaus

  Florida International University

  60 shared

• William J. Ripple

  Oregon State University

  47 shared

• Thomas M. Newsome

  University of Sydney

  47 shared

• Mike Letnic

  31 shared

• Robert L. Beschta

  Oregon State University

  31 shared

• Michael Nelson

  Oregon State University

  29 shared

• Christopher Wolf

  Oregon State University

  29 shared

• José Vicente López‐Bao

  Universidad de Oviedo

  28 shared

Labs

• Wirsing LabPI