Odocoileus Hemionus Sitkensis Research Articles

A comparison of thermal drones and camera trap population estimates for Sitka black‐tailed deer in Alaska

One of the most difficult challenges for wildlife managers is reliably estimating wildlife populations. Camera traps combined with spatial capture–recapture (SCR) models are a popular tool for population estimation. They have limitations, however, including long data processing times. Drones with thermal imagery are an emerging tool for estimating wildlife populations, but how they compare to other methods remain poorly studied. We compared the use of camera traps and SCR models to drone surveys for estimating population densities of Sitka black‐tailed deer Odocoileus hemionus sitkensis on Afognak Island, Alaska. We deployed 26 camera traps from 1 September until 6 October 2022 and individually identified males using antler characteristics, for the SCR model. At the same site we conducted three drone surveys between October and December 2022, identified sex composition and obtained deer counts. The estimated density from the SCR model was 3.7 males ± 0.8 (SE) km‐2, and 14.1 ± 3.1 adults km‐2 of clear‐cut forest. Results from the drone survey produced similar estimates with 2.1 ± 0.9 males km‐2 and 13.4 ± 1.6 adults km‐2. The similarity in estimates suggests that both methods converged on an accurate representation of the population in this habitat, but these methods diverge in levels of sampling effort, duration, and financial cost. Camera traps offer further insights on behavior and home‐range size but require longer data processing times, can be subject to malfunctions, and are difficult to deploy and maintain in remote areas. Drones are subject to legal restrictions, have difficulty in closed canopy habitat and can be initially costly, but they provide results faster and require less data analysis. Camera traps and drones are useful for determining population dynamics but are subject to their limitations. Wildlife managers should make survey decisions based on their specific goals, habitat type, focal species ecology and financial limitations.

Relative efficiency of hunting methods during an incomplete Sitka black‐tailed deer eradication on Haida Gwaii, Canada

Abstract Invasive species are reducing global biodiversity. The Llgaay gwii sdiihlda—Restoring Balance project was initiated to halt and reverse biodiversity loss on six islands on Haida Gwaii, Canada through the eradication of invasive Sitka Black‐tailed deer (Odocoileus hemionus sitkensis). Invasive deer were killed using various hunting methods including bait station, boat, aerial and indicator dog hunting as well as a combination of bailing dogs with boat and aerial hunting. Cost was quantified in terms of helicopter hunting hours ($1965 CAD/hr at the time of the study) to facilitate comparisons. Efficiency was quantified as the expected number of deer per helicopter hour. Hierarchical Bayesian integrated removal models were used to estimate the change in efficiency of the various hunting methods with deer density based on a power function. The models used the number of scent trail detections by dogs at the end of the study to help parameterise the population density. At densities between 2 and 30 deer/km2, boat hunting was estimated as the most efficient method while at lower densities indicator dog hunting was most efficient. The eradication was incomplete. The estimated cost to completion using indicator dog hunting for each island was 43 helicopter hours (~$84,000) on Ramsay Island (95% CI = 19–128), 3.9 helicopter hours on Murchison Island (95% CI = 0.56–18) and no additional hours on House (95% CI = 0–1.6) though the selected method would likely have been indicator dogs with combined hunting due to the variable terrain. Lessons learned: DNA connectivity analysis can be used to determine project durability, pilot studies to confirm method efficiency in local context will increase the chances of success, local knowledge improves efficiency of hunting methods, population and efficiency estimates should be updated throughout operations to allow adaptive management, eradications on ungulates can include pauses to facilitate adaptive management, the level of certainty for determining eradication completion should be determined in advance of operations with explicit trade‐offs identified for managers.

Past population control biases interpretations of contemporary genetic data: implications for future invasive Sitka black-tailed deer management in Haida Gwaii

Past population control biases interpretations of contemporary genetic data: implications for future invasive Sitka black-tailed deer management in Haida Gwaii

Recovery of a marine keystone predator transforms terrestrial predator–prey dynamics

Sea otters (Enhydra lutris) and wolves (Canis lupus) are two apex predators with strong and cascading effects on ecosystem structure and function. After decades of recovery from near extirpation, their ranges now overlap, allowing sea otters and wolves to interact for the first time in the scientific record. We intensively studied wolves during 2015 to 2021 in an island system colonized by sea otters in the 2000s and by wolves in 2013. After wolf colonization, we quantified shifts in foraging behavior with DNA metabarcoding of 689 wolf scats and stable isotope analyses, both revealing a dietary switch from Sitka black-tailed deer (Odocoileus hemionus), the terrestrial insitu primary prey, to sea otters. Here we show an unexpected result of the reintroduction and restoration of sea otters, which became an abundant marine subsidy for wolves following population recovery. The availability of sea otters allowed wolves to persist and continue to reproduce, subsequently nearly eliminating deer. Genotypes from 390 wolf scats and telemetry data from 13 wolves confirmed island fidelity constituting one of the highest known wolf population densities and upending standardly accepted wolf density predictions based on ungulate abundance. Whereas marine subsidies in other systems are generally derived from lower trophic levels, here an apex nearshore predator became a key prey species and linked nearshore and terrestrial food webs in a recently deglaciated and rapidly changing ecosystem. These results underscore that species restoration may serve as an unanticipated nutrient pathway for recipient ecosystems even resulting in cross-boundary subsidy cascades.

A genotyping-in-thousands by sequencing panel to inform invasive deer management using noninvasive fecal and hair samples.

Studies in ecology, evolution, and conservation often rely on noninvasive samples, making it challenging to generate large amounts of high‐quality genetic data for many elusive and at‐risk species. We developed and optimized a Genotyping‐in‐Thousands by sequencing (GT‐seq) panel using noninvasive samples to inform the management of invasive Sitka black‐tailed deer (Odocoileus hemionus sitkensis) in Haida Gwaii (Canada). We validated our panel using paired high‐quality tissue and noninvasive fecal and hair samples to simultaneously distinguish individuals, identify sex, and reconstruct kinship among deer sampled across the archipelago, then provided a proof‐of‐concept application using field‐collected feces on SGang Gwaay, an island of high ecological and cultural value. Genotyping success across 244 loci was high (90.3%) and comparable to that of high‐quality tissue samples genotyped using restriction‐site associated DNA sequencing (92.4%), while genotyping discordance between paired high‐quality tissue and noninvasive samples was low (0.50%). The panel will be used to inform future invasive species operations in Haida Gwaii by providing individual and population information to inform management. More broadly, our GT‐seq workflow that includes quality control analyses for targeted SNP selection and a modified protocol may be of wider utility for other studies and systems where noninvasive genetic sampling is employed.

Population genomics of Sitka black-tailed deer supports invasive species management and ecological restoration on islands

Invasive mammals represent a critical threat to island biodiversity; eradications can result in ecological restoration yet may fail in the absence of key population parameters. Over-browsing by invasive Sitka black-tailed deer (Odocoileus hemionus sitkensis) is causing severe ecological and cultural impacts across the Haida Gwaii archipelago (Canada). Previous eradication attempts demonstrate forest regeneration upon deer removal, but reinvasion reverses conservation gains. Here we use restriction-site associated DNA sequencing (12,947 SNPs) to investigate connectivity and gene flow of invasive deer (n = 181) across 15 islands, revealing little structure throughout Haida Gwaii and identifying the large, central island of Moresby (>2600 km2) as the greatest source of migrants. As a result, the archipelago itself should be considered the primary eradication unit, with the exception of geographically isolated islands like SGang Gwaay. Thus, limiting eradications to isolated islands combined with controlled culling and enhanced biosecurity may be the most effective strategies for achieving ecological restoration goals.

Using LiDAR and Random Forest to improve deer habitat models in a managed forest landscape

Conservation strategies are hindered by a lack of accurate maps of important habitat for many wildlife species, but especially for species inhabiting managed forest landscapes. Prioritizing restoration efforts on Alaska’s Tongass National Forest from past extensive clearcut logging is extremely challenging given the difficulty in accurately mapping its remote, rugged temperate rainforest landscapes. We tested the application of airborne light detection and ranging (LiDAR) technology to build a winter habitat model for Sitka black-tailed deer (Odocoileus hemionus sitkensis), the primary herbivore in the coastal temperate rainforest. We analyzed the importance of geomorphometric and forest structure characteristics as predictors of deer winter habitat selection using Random Forest applied to a 3-year GPS relocation dataset collected from 40 adult female deer. The LiDAR-based habitat model had a predictive performance of 94% (Out-of-bag error = 6%), a 10% lower model error compared to air-photo interpreted polygons and modeled plot data. Random Forest also outperformed analogous resource selection function models based on a comprehensive k-fold cross-validation. Deer habitat selection patterns in the LiDAR-based model were nonlinear across geomorphometric and forest structure predictive variables, and generally supported existing studies of deer habitat selection. Besides improving deer conservation and management on the Tongass National Forest, our approach could greatly enhance the accuracy and resolution of habitat maps used for conservation and restoration planning across large managed forest landscapes.

Resource use by an apex mesocarnivore, Pacific marten, in a highly modified forested island ecosystem

Apex mesocarnivores can have a large influence on the functioning of plant and animal communities. Such effects can be more pronounced in relatively depauperate island ecosystems, especially in the context of a legacy of landscape change and introduced species. One such ecosystem is Haida Gwaii, British Columbia, Canada, where a long history of introduced species and forest harvesting has greatly influenced the composition of the plant and animal communities. Most notably, Sitka black-tailed deer (Odocoileus hemionus sitkensis), an introduced and unchecked invasive species, has interacted with forest harvesting to greatly change the understory structure and composition of those temperate rainforests. Little is known of the habitat ecology of Pacific marten (Martes caurina), the small-bodied apex predator on those islands. We used camera traps to monitor the distribution and habitat ecology of marten across 2 winters. We used mixed-effects logistic regression to test 14 a priori hypotheses represented by statistical models formulated at two spatial scales (100 and 1000 m), with four categories of explanatory factors: sampling bias, forest structure, topography, and human disturbance. Relationships between detections and covariates from the top models revealed that at the 100-m scale, marten were more likely to use habitat that was closer to streams and marine shorelines and that contained a small area of forest harvesting. Marten detections were associated with habitat containing some component of forest edge and road, suggesting foraging behavior adapted to invasive deer, an important source of carrion for marten during winter. The broad use of habitats by Pacific marten suggests that intraguild competition and predation might occur with several species at risk including the endemic Haida ermine (Mustela ermine haidarum). Those two species would likely overlap in diet and distribution when co-occurring across low-elevation coastal habitats. Conservation planning on Haida Gwaii should consider measures that decrease the potential for competition or predation between marten and species at risk.

Spatial and temporal variability in the diet of Pacific marten (Martes caurina) on Haida Gwaii: an apex predator in a highly modified ecosystem

Knowledge of the diet ecology of apex predators in insular island ecosystems has direct applications to the conservation of endemic species at risk of extinction. We used stable isotopes of carbon and nitrogen to infer resource-use strategies of an indigenous predator, the Pacific marten (Martes caurina (Merriam, 1890)), in a highly modified ecosystem on Haida Gwaii, British Columbia, Canada. We used Bayesian isotopic mixing models to estimate the relative contributions of different food sources to marten diet across seasons and during overall lifetime, and to determine how diet varied with different levels of access to marine resources. Isotopes of carbon and nitrogen measured in hair and muscle tissue suggested that marten consumed salmon (3%–17%) and berries (25%–37%) seasonally; these diet groups were relatively minor components of the lifetime diet. Analysis of bone collagen suggested that terrestrial fauna — including birds, deer, small mammals, and invertebrates — contributed the most to diet (41%–55%), and marine invertebrates (38%–48%), not salmon (0%–3%), were the main allochthonous marine nutrient subsidy to lifetime diet. Plasticity in foraging ecology, combined with a broad dietary niche, introduced prey, notably the invasive Sitka black-tailed deer (Odocoileus hemionus sitkensis Merriam, 1898), as well as abundant marine resources, may allow marten to outcompete other indigenous and endemic carnivores on Haida Gwaii.

The Importance of Environmental Variability and Transient Population Dynamics for a Northern Ungulate

The pathways through which environmental variability affects population dynamics remain poorly understood, limiting ecological inference and management actions. Here, we use matrix-based population models to examine the vital rate responses to environmental variability and individual traits, and subsequent transient dynamics of the population in response to the environment. Using Sitka black-tailed deer (Odocoileus hemionus sitkensis) in Southeast Alaska as a study system, we modeled effects of inter-annual process variance of covariates on female survival, pregnancy rate, and fetal rate, and summer and winter fawn survival. To examine the influence of environmental variance on population dynamics, we compared asymptotic and transient perturbation analysis (elasticity analysis, a life-table response experiment, and transience simulation). We found that summer fawn survival was primarily determined by black bear (Ursus americanus) predation and was positively influenced by mass at birth and female sex. Winter fawn survival was determined by malnutrition in deep-snow winters and was influenced by an interaction between date of birth and snow depth, with late-born fawns at greater risk in deep-snow winters. Adult female survival was the most influential vital rate based on classic elasticity analysis, however, elasticity analysis based on process variation indicated that winter and summer fawn survival were most variable and thus most influential to variability in population growth. Transient dynamics produced by non-stable stage distributions produced realized annual growth rates different from predicted asymptotic growth rates in all years, emphasizing the importance of winter perturbations to population dynamics of this species.

Deer slow down litter decomposition by reducing litter quality in a temperate forest

Litter decomposition is a key process that allows the recycling of nutrients within ecosystems. In temperate forests, the role of large herbivores in litter decomposition remains a subject of debate. To address this question, we used two litterbag experiments in a quasiexperimental situation resulting from the introduction of Sitka black-tailed deer Odocoileus hemionus sitkensis on forested islands of Haida Gwaii (Canada). We investigated the two main pathways by which deer could modify litter decomposition: change in litter quality and modification of decomposer communities. We found that deer presence significantly reduced litter mass loss after 1 yr, mainly through a reduction in litter quality. This mass loss reflected a 30 and 28% lower loss of carbon (C) and nitrogen (N), respectively. The presence of deer also reduced the ability of decomposers to break down carbon, but not nitrogen. Indeed, litter placed on an island with deer lost 5% less carbon after 1 yr of decomposition than did litter decomposing on an island without deer. This loss in ability to decompose litter in the presence of deer was outweighed by the differences in mass loss associated with the effect of deer on litter quality. Additional effects of feces deposition by deer on the decomposition process were also significant but minor. These results suggest that the effects dramatic continental-scale increases in deer populations may have on broad-scale patterns of C and N cycling deserve closer attention.

Effects on understory biomass and forage 8–10 years after precommercial thinning of Sitka spruce – western hemlock stands in southeast Alaska

In southeast Alaska, United States, multiple-use forest management objectives include both timber production and wildlife habitat. Following stand-replacing disturbances such as clear-cutting, Sitka spruce (Picea sitchensis (Bong.) Carrière) and western hemlock (Tsuga heterophylla (Raf.) Sarg.) naturally regenerate and competitively dominate resources, excluding understory biomass and biodiversity. Thinning may mitigate the effects of canopy closure and permit understory development, but evidence of the effect on understories 8–10 years after thinning is lacking. We report results 4–5 and 8–10 years after thinning experiments on the Tongass National Forest to demonstrate the effects of precommercial thinning (thinned versus control), stand age (15–25, 25–35, and 35–50 years), and weather on understory dynamics and Sitka black-tailed deer (Odocoileus hemionus sitkensis Merriam, 1898) forage availability. Stand density negatively affected understory biomass, whereas temperature and precipitation positively interacted to increase biomass. Thinning had an enduring effect on understories, with biomass at least twice as great in thinned versus unthinned stands through year 10. We identified compositional differences from thinning as stand age class increased. Deer forage responded similarly to biomass, but thinning-induced differences faded with increased winter snowfall scenarios, especially in older stands. This study aids the understanding of stand overstory and understory development following silvicultural treatments in the coastal temperate rain forest of Alaska and suggests management implications and applications for balancing objectives throughout the forest type.

Orf virus infection in Alaskan mountain goats, Dall\u2019s sheep, muskoxen, caribou and Sitka black-tailed deer

BackgroundThe zoonotic Orf virus (ORFV; genus Parapoxvirus, Poxviridae family) occurs worldwide and is transmitted between sheep and goats, wildlife and man. Archived tissue samples from 16 Alaskan wildlife cases, representing mountain goat (Oreamnos americanus, n = 8), Dall’s sheep (Ovis dalli dalli, n = 3), muskox (Ovibos moschatus, n = 3), Sitka black-tailed deer (Odocoileus hemionus sitkensis, n = 1) and caribou (Rangifer tarandus granti, n = 1), were analyzed.ResultsClinical signs and pathology were most severe in mountain goats, affecting most mucocutaneous regions, including palpebrae, nares, lips, anus, prepuce or vulva, as well as coronary bands. The proliferative masses were solid and nodular, covered by dark friable crusts. For Dall’s sheep lambs and juveniles, the gross lesions were similar to those of mountain goats, but not as extensive. The muskoxen displayed ulcerative lesions on the legs. The caribou had two ulcerative lesions on the upper lip, as well as lesions on the distal part of the legs, around the main and dew claws. A large hairless spherical mass, with the characteristics of a fibroma, was sampled from a Sitka black-tailed deer, which did not show proliferative lesions typical of an ORFV infection. Polymerase chain reaction analyses for B2L, GIF, vIL-10 and ATI demonstrated ORFV specific DNA in all cases. Sequences from Dall’s sheep formed a separate cluster, comparable to ORFV from domestic sheep. Sequences from the other species were different from the Dall’s sheep sequences, but almost identical to each other.ConclusionsThis is the first major investigation of parapoxvirus infections in large Alaskan game species, and the first report of parapoxvirus infection in caribou and Sitka black-tailed deer. This study shows that most of the wild ruminant species in Alaska and from most parts of Alaska, can carry and be affected by ORFV. These findings call for attention to transmission of ORFV from wildlife to livestock and to hunters, subsistence harvesters, and wildlife biologists.

Resource selection by coastal wolves reveals the seasonal importance of seral forest and suitable prey habitat

Abstract Wolves (Canis lupus) in Southeast Alaska inhabit temperate rainforests characterized by patchworks of old-growth and harvested forest stands in various stages of regeneration. Investigating wolf space-use patterns in this landscape may yield information on their tolerance of anthropogenic disturbance in forest ecosystems. Furthermore, identifying shifts in habitat selection throughout the year can provide insights into wolves’ ability to exploit seasonally available resources. We examined seasonal habitat selection of wolves on Prince of Wales Island, Alaska with respect to forest structure, succession, land cover, topography, road densities and habitat predicted to support Sitka blacked-tailed deer (Odocoileus hemionus sitkensis) and salmon (Onchorynchus spp.), the primary and a secondary prey species. We used GPS locations from 13 wolves during 2012–2016 to develop resource selection functions (RSFs). Within their home ranges, wolves selected low elevation, flat terrain with open land cover and low-volume old-growth forests across seasons. During fall and winter wolves preferred clearcuts ≤30 years old, but avoided clearcuts >30 years old and thinned young-growth relative to medium-volume old growth. Habitats with predicted high deer carrying capacities were selected during late summer and fall, and areas close to anadromous streams were important only during summer when salmon were spawning. Areas of high road densities were avoided during denning season and summer, but strongly selected during winter. Our study reveals the potential of coastal wolves to seasonally target prey habitat and adjust to altered landscapes, but successional forests had a limited period of use (

Behavioral plasticity in a variable environment: snow depth and habitat interactions drive deer movement in winter

In seasonally varying environments, animals should alter habitat selection through time to avoid the harshest conditions. Winter severity is limiting for many ungulates in high-latitude ecosystems, and quality of habitat is an important determinant of winter survival. Previous studies in Southeast Alaska indicated that Sitka black-tailed deer (Odocoileus hemionus sitkensis) selected old-growth forest that provides both snow interception and forage, but with great variability among studies, years, and geographic areas. Clearcut timber harvest has greatly reduced the extent and quality of old-growth forest. The value of 2nd-growth and old-growth forest types to deer likely depends on snow depth, which is highly variable in space and time. We measured selection for vegetation classes, landscape features, and forage biomass by monitoring 56 GPS-radiocollared adult female deer from 1 January to 1 April between 2011 and 2013. Simultaneously, we measured snow depth across deer home ranges daily. We determined that snow depth had a strong effect on selection for vegetation classes. During periods of low snow, deer selected young 2nd growth but avoided old 2nd growth and high-volume old growth. As snow depths increased, young 2nd growth was avoided and deer selected old 2nd-growth and productive old-growth forests. The composition of vegetation classes within the landscape influenced selection, with deer selecting locally abundant habitats. These behaviors suggest that the widespread distribution of forest patches that provide snow interception and forage biomass may be critical to fulfilling the energetic requirements of deer during winters with snow. Such context-dependent habitat selection is likely widespread among wildlife species in variable environments and should be incorporated into study design and analysis.

Considerations on neonatal ungulate capture method: potential for bias in survival estimation and cause‐specific mortality

A recent study of Sitka black‐tailed deer Odocoileus hemionus sitkensis demonstrated that opportunistic fawn capture yielded left‐truncated data and ultimately resulted in overestimating fawn survival and spurious ecological model inference compared to neonates captured via vaginal implant transmitters (VITs). Given the ecological and economic value of ungulates worldwide and the importance of neonate survival to understanding population dynamics, the potential biases in survival estimates and causes of mortality caused by left‐truncation must be transparent. Herein, we used a VIT‐based dataset from white‐tailed deer Odocoileus virginianus to examine potential problems with left‐truncated data. We manipulated our original VIT‐based dataset by randomly assigning age‐at‐capture to create three hypothetical opportunistic samples. We used the Kaplan—Meier estimator to quantify fawn survival to 16 weeks of age for the original and hypothetical datasets. Additionally, we compared the relative importance of mortality causes between the datasets. Survival for the original, VIT‐based dataset was 0.121 (SE = 0.043), while hypothetical datasets yielded overestimates (ranging from 0.191 to 0.234). The hypothetical opportunistic samples overestimated coyote predation as a source of mortality, while underestimating starvation. Because management actions rely on accurate estimates of survival and causes of mortality, we recommend that neonatal survival studies consider biases caused by capture method. For robust estimates of survival, VIT‐based samples appear to provide better estimates of survival, as opportunistic samples are biased high. We encourage future work to elucidate the potential for neonate capture technique to affect cause‐specific mortality.

Levels of fecal glucocorticoid metabolites do not reflect environmental contrasts across islands in black-tailed deer (Odocoileus hemionus sitkensis) populations

Animals face stressful situations to which they can respond by mounting a physiological response. Few studies have compared the relative effects of two or more stressors on this response. We compared how low food abundance and hunting affected levels of fecal glucocorticoid metabolites (FGM), an indicator of stress, in Sitka black-tailed deer (Odocoileus hemionus sitkensis) on the Haida Gwaii archipelago (Canada). We monitored monthly FGM levels over a year on three islands: on two, there was no hunting but deer were exposed to increased risk of severe food depletion; and on one, deer had access to abundant food but were exposed to a few days of hunting each year. Based on the context of the study, we tentatively predicted that FGM levels would be higher in low food abundance/safe islands. We also predicted that FGM levels would be higher in winter when food is rarer, particularly in low food abundance/safe islands. The three deer populations presented similar average FGM levels and seasonal variations. Our predictions were therefore not supported. Our results rather suggested that environmental contrasts, perceived by us as large (increased risk of starvation on ELI and Kunga islands) or associated with differences in animal behavior (human avoidance on Reef island), did not lead to increased stress responses. We discuss plausible explanations, including the down-regulation of the stress response in depleted environments and the lack of stress response to low hunting pressure when behavioral responses to risk are unlikely to be costly.

Sitka black-tailed deer (Odocoileus hemionus sitkensis) adjust habitat selection and activity rhythm to the absence of predators

Although individuals must generally trade off acquisition of high-quality resources against predation risk avoidance, removal of top predators by humans has resulted in many large herbivores experiencing novel conditions where their natural predators are absent. Antipredator behaviors should be attenuated or lost in such a context of relaxed predation pressure. To test this prediction, we analyzed daily and seasonal habitat selection and activity rhythm (both commonly linked to predation risk) of GPS-collared Sitka black-tailed deer (Odocoileus hemionus sitkensis Merriam, 1898) on predator-free islands (British Columbia, Canada). In marked contrast to the behavioral patterns commonly observed in populations subject to predation risk, we documented a very low day–night contrast in habitat selection. Moreover, we observed higher activity during daytime than nighttime, as expected for nonhunted populations. We also showed that resource selection was primarily driven by seasonal variations in resource availability. These results are consistent with the expected attenuation of antipredator behaviors in predation-free environments. However, we also observed marked crepuscular activity peaks, which are commonly interpreted as an antipredator response in ungulates. Our study indicates that large herbivores are able to adjust certain antipredator behaviors under relaxed selection, notably habitat selection and activity rhythm, while others persist despite the long-term absence of predators.

Yellow‐cedar: climate change and natural history at odds

Yellow‐cedar: climate change and natural history at odds

Seeing a Ghost? Vigilance and Its Drivers in a Predator‐free World

AbstractVigilance is a key to the early detection of predators, but may be costly if it impairs foraging efficiency. Hence, we would expect vigilance to be suppressed and/or counter‐selected in predator‐free environments, although this might depend on the environmental drivers influencing perceived predation risk. We studied vigilance in two populations of Sitka black‐tailed deer (Odocoileus hemionus sitkensis) on Haida Gwaii (Canada) which have not been exposed to predators since they colonized the study islands approx. 60 yr ago. In this context, anti‐predator behavior should not have any obvious current benefit. Moreover, its maintenance should be particularly costly in our study populations because these deer have depleted their food resources and, thus, anti‐predator behaviors should interfere with time spent searching for scarce resources. We used bait stations equipped with camera traps to assess vigilance under standardized feeding conditions. We expected to observe lower vigilance levels than those observed elsewhere in locations with predators. We investigated how vigilance varied in relation to the amount of bait, the level of visibility, and between day and night. During the day, deer spent, on average, 14% of their time in overt vigilance during foraging bouts, a level similar to, although in the lower range of, values reported at sites where predators are present. Levels of vigilance were lower at night, and decreased with increasing visibility, but not during the day. Deer were less vigilant when bait availability was high, but only when visibility was also high. We discuss why the maintenance of vigilance is here best explained by the ghosts of predators past, and how, at the temporal scale of a few generations, the ecological factors driving vigilance levels might override the absence of significant risk from large predators.