Black bear (Ursus americanus) and wolf (Canis spp.) summer diet composition and ungulate prey selectivity in Ontario, Canada

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

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.

The ethology of wolves foraging on freshwater fish in a boreal ecosystem

Through global positioning system (GPS) collar locations, remote cameras, field observations and the first wild wolf to be GPS-collared with a camera collar, we describe when, where and how wolves fish in a freshwater ecosystem. From 2017 to 2021, we recorded more than 10 wolves (Canis lupus) hunting fish during the spring spawning season in northern Minnesota, USA. Wolves ambushed fish in creeks at night when spawning fish were abundant, available and vulnerable in shallow waters. We observed wolves specifically targeting sections of rivers below beaver (Castor canadensis) dams, suggesting that beavers may indirectly facilitate wolf fishing behaviour. Wolves also cached fish on shorelines. We documented these findings across five different social groups at four distinct waterways, suggesting that wolf fishing behaviour may be widespread in similar ecosystems but has probably remained difficult to study given its annual brevity. Spawning fish may serve as a valuable pulsed resource for packs because the spring spawning season coincides with low primary prey (deer Odocoileus virginianus) availability and abundance, and when packs have higher energetic demands owing to newly born pups. We demonstrate the flexibility and adaptability of wolf hunting and foraging behaviour, and provide insight into how wolves can survive in a myriad of ecosystems.

Diet flexibility of wolves and black bears in the range of migratory caribou

The diet of predators can be highly variable, which is exemplified by their ability to acclimate to a wide range of ecological conditions. Such flexibility in foraging may be a key aspect of their performance in unpredictable environments such as at the edge of the range of a species or where food availability varies greatly in time and space. Gaining information on the diets of predators under such conditions could foster our comprehension of their ecological flexibility and the potential role of predation on the population dynamics of prey. We determined the diet of wolves (Canis lupus) and black bears (Ursus americanus) in northern Québec and Labrador (Canada) within the range of two migratory caribou (Rangifer tarandus) herds: the high-abundance Rivière-aux-Feuilles herd (RFH) and low-abundance Rivière-George herd (RGH). Worldwide, decline in caribou populations has become a concern, stressing the need to better understand the factors involved in these declines, including predation. In northern Québec (RFH range), caribou was the primary year-round prey of wolves while moose (Alces alces) and muskoxen (Ovibos moschatus) were consumed in some sectors. The diet of wolves in northern Labrador (RGH range) varied seasonally, with caribou, moose, and fish as main prey during different periods throughout the year. Black bear diets varied seasonally and regionally. Among the foods we analyzed, caribou was the main source of animal protein for bears in northern Québec and northern Labrador, except during a high abundance of Ungava collared lemming (Dicrostonyx hudsonius). Only bears in northern Québec ate caribou during late summer/fall. Our results highlight the diet flexibility of wolves and black bears in northern food webs, and how their diets change in relation to the distribution and abundance of prey. Our results will help quantify the potential impact of these predators on prey populations in northern systems.

Lead exposure in American black bears increases with age and big game harvest density

Hunting has multiple consequences for wildlife, and it can be an important source of environmental pollution. Most big game hunters use lead (Pb) ammunition that shed metal fragments in the tissues of harvested animals. These Pb fragments become available to scavengers when hunters discard contaminated slaughter remains in the environment. This exposure route has been extensively studied in avian scavengers, but few studies have investigated Pb exposure from ammunition in mammals. Mammalian scavengers, including American black bears (Ursus americanus), frequently use slaughter remains discarded by hunters. The objective of this study was to investigate whether big game harvest density influenced long-term Pb exposure in American black bears from Quebec, Canada. Our results showed that female black bears had higher tooth Pb concentrations in areas with higher big game harvest densities, but such relationship was not evident in males. We also showed that older bears had higher tooth Pb concentrations compared to younger ones. Overall, our study showed that Pb exposure increases with age in black bears and that some of that Pb likely comes from bullet fragments embedded in slaughter remains discarded by hunters. These results suggest that hunters may drive mammalian scavengers into an evolutionary trap, whereby the long-term benefits of consuming slaughter remains could be negated due to increased Pb exposure.

Trophic niche partitioning between two prey and their incidental predators revealed various threats for an endangered species

Documenting trophic niche partitioning and resource use within a community is critical to evaluate underlying mechanisms of coexistence, competition, or predation. Detailed knowledge about foraging is essential as it may influence the vital rates, which, in turn, can affect trophic relationships between species, and population dynamics. The aims of this study were to evaluate resource and trophic niche partitioning in summer/autumn between the endangered Atlantic-Gaspésie caribou (Rangifer tarandus caribou) population, moose (Alces americanus) and their incidental predators, the black bear (Ursus americanus) and coyote (Canis latrans), and to quantify the extent to which these predators consumed caribou. Bayesian isotopic analysis showed a small overlap in trophic niche for the two sympatric ungulates suggesting a low potential for resource competition. Our results also revealed that caribou occupied a larger isotopic niche area than moose, suggesting a greater diversity of resources used by caribou. Not surprisingly, coyotes consumed mainly deer (Odocoileus virginianus), moose, snowshoe hare (Lepus americanus), and occasionally caribou, while bears consumed mainly vegetation and, to a lesser extent, moose and caribou. As coyotes and bears also feed on plant species, we documented trophic niche overlap between caribou and their predators, as searching for similar resources can force them to use the same habitats and thus increase the encounter rate and, ultimately, mortality risk for caribou. Although the decline in the Gaspésie caribou population is mostly driven by habitat-mediated predation, we found evidence that the low level of resource competition with moose, added to the shared resources with incidental predators, mainly bears, may contribute to jeopardize the recovery of this endangered caribou population. Highlighting the trophic interaction between species is needed to establish efficient conservation and management strategies to insure the persistence of endangered populations. The comparison of trophic niches of species sharing the same habitat or resources is fundamental to evaluate the mechanisms of coexistence or competition and eventually predict the consequences of ecosystem changes in the community.

Dietary niches of creodonts and carnivorans of the late Eocene Cypress Hills Formation

Modern North American carnivorous mammal assemblages consist of species from a single clade: the Carnivora. Carnivorans once coexisted with members of other meat-eating clades, including the creodonts (Hyaenodontida and Oxyaenida). Creodonts, however, went extinct in North America during the late Eocene and early Oligocene, potentially due to niche overlap and resource competition with contemporary carnivorans. In this study, we employ a community ecology approach to understand whether the dietary niches of coexisting creodonts and carnivorans overlapped during the late Eocene (Chadronian North American Land Mammal Age), a time when creodonts were dwindling and carnivorans were diversifying. We quantify niche overlap based on inferences of diet from carnassial tooth shape estimated using Orientation Patch Count, Dirichlet's Normal Surface Energy, and linear dental measurements as well as from body mass for all species in the Calf Creek Local Fauna of Cypress Hills, Saskatchewan (Treaty 4 land). Although creodonts and carnivorans shared characteristics of their carnassial tooth shape, suggesting similar chewing mechanics and feeding habits, we find that marked differences in body size likely facilitated niche partitioning, at least between the largest creodonts and carnivorans. Calculations of prey focus masses and prey mass spectra indicate that only the smallest creodont may have experienced significant competition for prey with the coeval carnivorans. We suggest that the ultimate extinction of creodonts from North America during the late Eocene and Oligocene was unlikely to have been driven by factors related to niche overlap with carnivorans.

Spring diet of American black bears (Ursus americanus) in a moose (Alces alces) – woodland caribou (Rangifer tarandus caribou) system in northern Ontario, Canada

American black bears (Ursus americanus Pallas, 1780) are opportunistic foragers, and across most of their range in North America, their diet is predominantly vegetation with limited consumption of vertebrates and invertebrates. However, they are also predators of ungulates, especially neonates, with regional variation in the amount of predation pressure they exert. We used scat analysis to examine the diet of black bears during the calving season in a moose (Alces alces (Linnaeus, 1758)) – woodland caribou (Rangifer tarandus caribou (Gmelin, 1788)) system in the Boreal forest of northern Ontario, Canada. Bears consumed herbaceous plants (46.5%), fruits and (or) seeds (20.0%), moose (3.3% adults; 4.3% calves), American beaver (Castor canadensis Kuhl, 1820; 8.5%), and insects (mostly ants; 4.2%). Bears had the highest consumption of moose and beaver in early spring, before switching to a more vegetation-dominated diet. We did not detect evidence of caribou consumption. Based on our results, black bear consumption of moose, particularly neonates, may warrant further investigation.

Wolf habitat selection in relation to recreational structures in a national park

Although most predators usually avoid human activity, some individuals instead will habituate to it. Habituation to human presence and infrastructure by predator species such as wolves may lead to conflicts implicating serious risks for public safety and for the survival of the animals involved. Accordingly, this research project aims to shed light on the relationship between wolves and recreational structures using telemetry data from 10 wolves located in the Parc National du Mont-Tremblant (Québec, Canada) and its surrounding area. Using resource selection functions (RSFs), we observed wolf habitat selection in relation to these structures during three biological periods (denning: May–June; rendezvous: June–October; and nomadic: October–April). Our results revealed that wolves selected proximity to linear structures (roads and trails) during the denning and rendezvous periods, but this selection depended on the density of such structures in the surroundings (i.e., functional response in habitat selection): wolves selected proximity to linear structures when these structures were present at greater densities. Wolves avoided housing structures (campsites, cabins, park facilities), especially when these structures were present at greater densities, suggesting that wolves perceived them as a risk. These results suggest that conflicts between visitors and wolves were unlikely to occur in campgrounds during the time of our study. This could indicate that the management measures implemented by the park following the past episodes of conflict were effective. However, wolves’ use of linear structures could lead to increased tolerance to human proximity if left unmanaged.

Iberian Lynx Lynx pardinus Temminck, 1827 (Mammalia: Carnivora: Felidae) in central Spain: trophic niche of an isolated population

Understanding predator-prey relationships is fundamental to develop effective conservation plans.  Between 2015 and 2018, we combed 21 transects, each 7km long, searching for Iberian Lynx Lynx pardinus scat within the province of Madrid in central Spain.  In order to minimise inherent subjectivity of visual identification as much as possible, we performed a double specific nested polymerase chain reaction (PCR) followed by a primer extension assay addressed to two Iberian Lynx diagnostic single nucleotide polymorphisms.  Forty-six scat samples were positively identified as belonging to Iberian Lynx through genetic analysis.  From these, we extracted remains of consumed prey, which we determined to the lowest possible taxonomic level, mainly through hair identification.  Identified prey was divided into four types: lagomorphs, small mammals, birds, and ungulates.  The species’ diet composition was described based on the frequency of occurrence (FO) of each prey and niche breadth, and also compared with prior knowledge of the species using four prior studies as a comparative reference through the calculation of the niche overlap value.  The FO of lagomorphs (39%) was the lowest, while the FO of small mammals (54%) was the highest recorded to date.  The niche breath (0.36) was higher than recorded in prior studies, but still showing the specialist character of the Iberian Lynx.  Niche overlap was low (C = 0.49), showing differences in trophic niche between the population in our study area and the one studied in southern Spain.  This indicates that the Iberian Lynx is adept at switching its main prey, an ability that has previously been firmly rejected.  It is, however, capable of adapting to alternative prey more often than recorded to date, which could be a behavioural response to the patchy distribution of European Rabbit Oryctolagus cuniculus in the study area.