Testing foraging optimization models in brown bears: Time for a paradigm shift in nutritional ecology?

How organisms obtain energy to survive and reproduce is fundamental to ecology, yet researchers use theoretical concepts represented by simplified models to estimate diet and predict community interactions. Such simplistic models can sometimes limit our understanding of ecological principles. We used a polyphagous species with a wide distribution, the brown bear (Ursus arctos), to illustrate how disparate theoretical frameworks in ecology can affect conclusions regarding ecological communities. We used stable isotope measurements (δ13 C, δ15 N) from hairs of individually monitored bears in Sweden and Bayesian mixing models to estimate dietary proportions of ants, moose, and three berry species to compare with other brown bear populations. We also developed three hypotheses based on predominant foraging literature, and then compared predicted diets to field estimates. Our three models assumed (1) bears forage to optimize caloric efficiency (optimum foraging model), predicting bears predominately eat berries (~70% of diet) and opportunistically feed on moose (Alces alces) and ants (Formica spp. and Camponotus spp; ~15% each); (2) bears maximize meat intake (maximizing fitness model), predicting a diet of 35%-50% moose, followed by ants (~30%), and berries (~15%); (3) bears forage to optimize macronutrient balance (macronutrient model), predicting a diet of ~22% (dry weight) or 17% metabolizable energy from proteins, with the rest made up of carbohydrates and lipids (~49% and 29% dry matter or 53% and 30% metabolizable energy, respectively). Bears primarily consumed bilberries (Vaccinium myrtillus; 50%-55%), followed by lingonberries (V. vitis-idaea; 22%-30%), crowberries (Empetrum nigrum; 8%-15%), ants (5%-8%), and moose (3%-4%). Dry matter dietary protein was lower than predicted by the maximizing fitness model and the macronutrient balancing model, but protein made up a larger proportion of the metabolizable energy than predicted. While diets most closely resembled predictions from optimal foraging theory, none of the foraging hypotheses fully described the relationship between foraging and ecological niches in brown bears. Acknowledging and broadening models based on foraging theories is more likely to foster novel discoveries and insights into the role of polyphagous species in ecosystems and we encourage this approach.

Coupled social and ecological change drove the historical extinction of the California grizzly bear (Ursus arctos californicus)

Large carnivores (order Carnivora) are among the world's most threatened mammals due to a confluence of ecological and social forces that have unfolded over centuries. Combining specimens from natural history collections with documents from archival records, we reconstructed the factors surrounding the extinction of the California grizzly bear (Ursus arctos californicus), a once-abundant brown bear subspecies last seen in 1924. Historical documents portrayed California grizzlies as massive hypercarnivores that endangered public safety. Yet, morphological measurements on skulls and teeth generate smaller body size estimates in alignment with extant North American grizzly populations (approx. 200 kg). Stable isotope analysis (δ13C, δ15N) of pelts and bones (n = 57) revealed that grizzlies derived less than 10% of their nutrition from terrestrial animal sources and were therefore largely herbivorous for millennia prior to the first European arrival in this region in 1542. Later colonial land uses, beginning in 1769 with the Mission era, led grizzlies to moderately increase animal protein consumption (up to 26% of diet), but grizzlies still consumed far less livestock than otherwise claimed by contemporary accounts. We show how human activities can provoke short-term behavioural shifts, such as heightened levels of carnivory, that in turn can lead to exaggerated predation narratives and incentivize persecution, triggering rapid loss of an otherwise widespread and ecologically flexible animal.

Toxic elements in arctic and sub-arctic brown bears: Blood concentrations of As, Cd, Hg and Pb in relation to diet, age, and human footprint

Contamination with arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb) is a global concern impairing resilience of organisms and ecosystems. Proximity to emission sources increases exposure risk but remoteness does not alleviate it. These toxic elements are transported in atmospheric and oceanic pathways and accumulate in organisms. Mercury accumulates in higher trophic levels. Brown bears (Ursus arctos), which often live in remote areas, are long-lived omnivores, feeding on salmon (Oncorhynchus spp.) and berries (Vaccinium spp.), resources also consumed by humans. We measured blood concentrations of As, Cd, Hg and Pb in bears (n = 72) four years and older in Scandinavia and three national parks in Alaska, USA (Lake Clark, Katmai and Gates of the Arctic) using high-resolution, inductively-coupled plasma sector field mass spectrometry. Age and sex of the bears, as well as the typical population level diet was associated with blood element concentrations using generalized linear regression models. Alaskan bears consuming salmon had higher Hg blood concentrations compared to Scandinavian bears feeding on berries, ants (Formica spp.) and moose (Alces). Cadmium and Pb blood concentrations were higher in Scandinavian bears than in Alaskan bears. Bears using marine food sources, in addition to salmon in Katmai, had higher As blood concentrations than bears in Scandinavia. Blood concentrations of Cd and Pb, as well as for As in female bears increased with age. Arsenic in males and Hg concentrations decreased with age. We detected elevated levels of toxic elements in bears from landscapes that are among the most pristine on the planet. Sources are unknown but anthropogenic emissions are most likely involved. All study areas face upcoming change: Increasing tourism and mining in Alaska and more intensive forestry in Scandinavia, combined with global climate change in both regions. Baseline contaminant concentrations as presented here are important knowledge in our changing world.

Black Bear Behavior and Movements Are Not Definitive Measures of Anthropogenic Food Use

Increasing human-bear conflicts are a growing concern, and managers often assume bears in developed areas are food-conditioned. We examined the relationship between human-bear conflicts and food conditioning by analyzing isotopic values of hair from black bears (Ursus americanus floridanus) involved in research (n = 34) and conflicts (n = 45). We separated research bears into wild and developed subgroups based on the impervious surface within their home ranges and separated conflict bears based on observations of human food consumption (anthropogenic = observations; management = no observations). We initially assumed wild bears were not food conditioned and anthropogenic bears were. However, using isotopic values, we classified 79% of anthropogenic bears and 8% of wild bears as food conditioned. Next, we assigned these bears to the appropriate food conditioned category and used the categorizations as a training set to classify developed and management bears. We estimated that 53% of management bears and 20% of developed bears were food conditioned. Only 60% of bears captured within or using developed areas showed evidence of food conditioning. We also found that δ13C values were a better predictor of anthropogenic foods in a bear's diet than δ15N values. Our results indicate that bears in developed areas are not necessarily food conditioned and caution against management actions based on limited observations of bear behavior.

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.

Phenotypic plasticity determines differences between the skulls of tigers from mainland Asia

Tiger subspecific taxonomy is controversial because of morphological and genetic variation found between now fragmented populations, yet the extent to which phenotypic plasticity or genetic variation affects phenotypes of putative tiger subspecies has not been explicitly addressed. In order to assess the role of phenotypic plasticity in determining skull variation, we compared skull morphology among continental tigers from zoos and the wild. In turn, we examine continental tiger skulls from across their wild range, to evaluate how the different environmental conditions experienced by individuals in the wild can influence morphological variation. Fifty-seven measurements from 172 specimens were used to analyse size and shape differences among wild and captive continental tiger skulls. Captive specimens have broader skulls, and shorter rostral depths and mandible heights than wild specimens. In addition, sagittal crest size is larger in wild Amur tigers compared with those from captivity, and it is larger in wild Amur tigers compared with other wild continental tigers. The degree of phenotypic plasticity shown by the sagittal crest, skull width and rostral height suggests that the distinctive shape of Amur tiger skulls compared with that of other continental tigers is mostly a phenotypically plastic response to differences in their environments.

Isotopic signature in isolated south-western populations of European brown bear (Ursus arctos)

Stable isotope analysis of animal tissue samples is increasingly used to study the trophic ecology of target species. The isotopic signatures respond to the type of diet, but also to the environmental conditions of their habitat. In the case of omnivorous, seasonal or opportunistic feeding species, the interpretation of isotopic values is more complex, as it is largely determined by food selection, either due to individual choice or because of availability. We analysed C and N isotopes in brown bear (Ursus arctos) hair from four isolated populations of south-western Europe (Cantabrian, Pyrenees, Central Apennines and Alpine) accounting for the geographical and climatic differences among the four areas. We found inter-population differences in isotopic signatures that cannot be attributed to climatic differences alone, indicating that at least some bears from relatively higher altitude populations experiencing higher precipitation (Pyrenees) show a greater consumption of animal foods than those from lower altitudes (Cantabrian and Apennines). The quantification of isotopic niche space using Layman’s metrics identified significant similarities between the Cantabrian and Central Apennine samples that markedly differ from the Pyrenean and Alpine. Our study provides a baseline to allow further comparisons in isotopic niche spaces in a broad ranged omnivorous mammal, whose European distribution requires further conservation attention especially for southern isolated populations.

Maternal carryover, winter severity, and brown bear abundance relate to elk demographics

Ungulates are key components of ecosystems due to their effects on lower trophic levels, role as prey, and value for recreational and subsistence harvests. Understanding factors that drive ungulate population dynamics can inform protection of important habitat and successful management of populations. To ascertain correlates of ungulate population dynamics, we evaluated the effects of five non-exclusive hypotheses on ungulate abundance and recruitment: winter severity, spring nutritional limitation (spring bottleneck), summer-autumn maternal condition carryover, predation, and timber harvest. We used weather, reconstructed brown bear (Ursus arctos) abundance, and timber harvest data to estimate support for these hypotheses on early calf recruitment (calves per 100 adult females in July–August) and population counts of Roosevelt elk (Cervus canadensis roosevelti) on Afognak and Raspberry islands, Alaska, USA, 1958–2020. Increasing winter temperatures positively affected elk abundance, supporting the winter severity hypothesis, while a later first fall freeze had a positive effect on elk recruitment, supporting the maternal carry-over hypothesis. Increased brown bear abundance was negatively associated with elk recruitment, supporting the predation hypothesis. Recruitment was unaffected by spring climate conditions or timber harvest. Severe winter weather likely increased elk energy deficits, reducing elk survival and subsequent abundance in the following year. Colder and shorter falls likely reduced late-season forage, resulting in poor maternal condition which limited elk recruitment more than winter severity or late-winter nutritional bottlenecks. Our results additionally demonstrated potential negative effects of brown bears on elk recruitment. The apparent long-term decline in elk recruitment did not result in a decline of abundance, which suggests that less severe winters may increase elk survival and counteract the potential effects of predation on elk abundance.

Ursids evolved early and continuously to be low-protein macronutrient omnivores

The eight species of bears world-wide consume a wide variety of diets. Some are specialists with extensive anatomical and physiological adaptations necessary to exploit specific foods or environments [e.g., polar bears (Ursus maritimus), giant pandas (Ailuropoda melanoleuca), and sloth bears (Melursus ursinus)], while the rest are generalists. Even though ursids evolved from a high-protein carnivore, we hypothesized that all have become low-protein macronutrient omnivores. While this dietary strategy has already been described for polar bears and brown bears (Ursus arctos), a recent study on giant pandas suggested their macronutrient selection was that of the ancestral high-protein carnivore. Consumption of diets with inappropriate macronutrient profiles has been associated with increased energy expenditure, ill health, failed reproduction, and premature death. Consequently, we conducted feeding and preference trials with giant pandas and sloth bears, a termite and ant-feeding specialist. Both giant pandas and sloth bears branched off from the ursid lineage a million or more years before polar bears and brown bears. We found that giant pandas are low-protein, high-carbohydrate omnivores, whereas sloth bears are low-protein, high-fat omnivores. The preference for low protein diets apparently occurred early in the evolution of ursids and may have been critical to their world-wide spread.

The influence of human disturbance on Pacific salmon (Oncorhynchus spp.) in the diet of American black bears (Ursus americanus) in two areas of coastal British Columbia, Canada

Recent studies have highlighted the importance of salmon (genus Oncorhynchus Suckley, 1861) in the diet of bears, and of bears as consumers and key agents supporting the transport of salmon-derived nutrients to riparian ecosystems. Salmon abundance and human disturbance are known influences on bear ecology and behaviour, though few studies have quantified shifts in bear diet due to these effects. We used stable isotope analysis to investigate how salmon escapement and human presence influenced the proportion of salmon in the diet of American black bears ( Ursus americanus Pallas, 1780) in two locations in coastal British Columbia, Canada. We found that salmon constituted a small proportion of black bear diet across sexes and ecosystems, while bears appeared to gain a similar amount of energy and lean mass from terrestrial sources. Salmon consumption was not related to the total annual abundance of salmon in a watershed but was significantly lower in large streams with regular human presence, suggesting that human disturbance can cause a dietary shift in bears that could have important consequences to their fitness. We also observed that the isotopic signatures of key bear foods did not vary between foliage and fruit, simplifying data collection for future isotopic studies on bear diet.

Gaining insight into the assimilated diet of small bear populations by stable isotope analysis

Apennine brown bears (Ursus arctos marsicanus) survive in an isolated and critically endangered population, and their food habits have been studied using traditional scat analysis. To complement current dietary knowledge, we applied Stable Isotope Analysis (SIA) to non-invasively collected bear hairs that had been individually recognized through multilocus genotyping. We analysed carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotopes of hair sections and bear key foods in a Bayesian mixing models framework to reconstruct the assimilated diet on a seasonal basis and to assess gender and management status effects. In total, we analysed 34 different seasonal bear key foods and 35 hair samples belonging to 27 different bears (16 females and 11 males) collected during a population survey in 2014. Most bears showed wide δ¹⁵N and δ¹³C ranges and individual differences in seasonal isotopic patterns. Vegetable matter (herbs, fleshy fruits and hard mast) represented the major component of the assimilated diet across the dietary seasons, whereas vegetable crops were rarely and C4 plants (i.e., corn) never consumed. We confirmed an overall low consumption of large mammals by Apennine bears consistently between sexes, with highest values in spring followed by early summer but null in the other seasons. We also confirmed that consumption of fleshy fruits peaked in late summer, when wild predominated over cultivated fleshy fruits, even though the latter tended to be consumed in higher proportion in autumn. Male bears had higher δ ¹⁵N values than females in spring and autumn. Our findings also hint at additional differences in the assimilated diet between sexes, with females likely consuming more herbs during spring, ants during early summer, and hard mast during fall compared to males. In addition, although effect sizes were small and credibility intervals overlapped considerably, management bears on average were 0.9‰ lower in δ ¹³C and 2.9‰ higher in δ ¹⁵N compared to non-management bears, with differences in isotopic values between the two bear categories peaking in autumn. While non-management bears consumed more herbs, wild fleshy fruits, and hard mast, management bears tended to consume higher proportions of cultivated fruits, ants, and large mammals, possibly including livestock. Although multi-year sampling and larger sample sizes are needed to support our findings, our application confirms that SIA can effectively integrate previous knowledge and be efficiently conducted using samples non-invasively collected during population surveys.

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.

Dining from the coast to the summit: Salmon and pine nuts determine the summer body condition of female brown bears on the Shiretoko Peninsula

Body condition in mammals fluctuates depending on energy intake and expenditure. For brown bears (Ursus arctos), high-protein foods facilitate efficient mass gain, while lipids and carbohydrates play important roles in adjusting dietary protein content to optimal levels to maximize energy intake. On the Shiretoko Peninsula, Hokkaido, Japan, brown bears have seasonal access to high-lipid pine nuts and high-protein salmon. To assess seasonal and annual fluctuation in the body condition of adult female brown bears in relation to diet and reproductive status, we conducted a longitudinal study in a special wildlife protection area on the Shiretoko Peninsula during 2012-2018. First, analyses of 2,079 bear scats revealed that pine nuts accounted for 39.8% of energy intake in August and salmon accounted for 46.1% in September and that their consumption by bears varied annually. Second, we calculated the ratio of torso height to torso length as an index of body condition from 1,226 photographs of 12 adult females. Results indicated that body condition continued to decline until late August and started to increase in September when salmon consumption increased. In addition, body condition began to recover earlier in years when consumption of both pine nuts and salmon was high. Furthermore, females with offspring had poorer body condition than solitary females, in particular in late August in years with low salmon consumption. Our findings suggest that coastal and subalpine foods, which are unique to the Shiretoko Peninsula, determine the summer body condition of female brown bears, as well as their survival and reproductive success.

Mapping potential effects of proposed roads on migratory connectivity for a highly mobile herbivore using circuit theory

Migration is common worldwide as species access spatiotemporally varying resources and avoid predators and parasites. However, long-distance migrations are increasingly imperiled due to development and habitat fragmentation. Improved understanding of migratory behavior has implications for conservation and management of migratory species, allowing identification and protection of seasonal ranges and migration corridors. We present a technique that applies circuit theory to predict future effects of development by analyzing season-specific resistance to movement from anthropogenic and natural environmental features across an entire migratory path. We demonstrate the utility of our approach by examining potential effects of a proposed road system on barren ground caribou (Rangifer tarandus granti) and subsistence hunters in northern Alaska. Resource selection functions revealed migratory selection by caribou. We tested five scenarios relating habitat selection to landscape resistance using Circuitscape and GPS telemetry data. To examine the effect of potential roads on connectivity of migrating animals and human hunters, we compared current flow values near communities in the presence of proposed roads. Caribou avoided dense vegetation, rugged terrain, major rivers, and existing roads in both spring and fall. A negative linear relationship between resource selection and landscape resistance was strongly supported for fall migration while spring migration featured a negative logarithmic relationship. Overall patterns of caribou connectivity remained similar in the presence of proposed roads, though reduced current flow was predicted for communities near the center of current migration areas. Such data can inform decisions to allow or disallow projects or to select among alternative development proposals and mitigation measures, though consideration of cumulative effects of development is needed. Our approach is flexible and can easily be adapted to other species, locations and development scenarios to expand understanding of movement behavior and to evaluate proposed developments. Such information is vital to inform policy decisions that balance new development, resource user needs, and preservation of ecosystem function.

Prevalence and patterns of scavenging by brown bears (Ursus arctos) on salmon (Oncorhynchus spp.) carcasses

Scavenging, an underappreciated mechanism of prey consumption for many predators, can contribute substantially to nutritional intake. Facultative scavengers such as brown bears (Ursus arctos Linnaeus, 1758) may both kill and scavenge Pacific salmon (genus Oncorhynchus Suckley, 1861), though the extent of scavenging and factors affecting this behavior are unclear. We tagged 899 sockeye salmon (Oncorhynchus nerka (Walbaum in Artedi, 1792)) carcasses and placed them on streambanks over 5 years at multiple sites in southwestern Alaska (USA) where brown bears annually prey on spawning sockeye salmon. Examination of carcasses revealed overall scavenging rates of 15% after 1 day and 54% after 3 days. Scavenging rate varied by site and year and increased throughout the salmon run. Contrary to predictions, scavenging was more frequent in senescent or bear-killed carcasses than ripe carcasses. Carcass consumption ranged from minimal to almost complete; body and brain tissues were most frequently consumed after 3 days (68% and 63% of carcasses, respectively). We also documented secondary scavenging (i.e., tissue consumption on two separate events) and delayed scavenging (i.e., scavenging observed after 3 days but not 1 day). Taken together, the results indicated that scavenging in these streams contributes significantly to total consumption of salmon by bears, with ramifications for other components of these salmon-dependent ecosystems.

Community Ecology and Conservation of Bear-Salmon Ecosystems

Apex predators play keystone roles in ecosystems through top-down control, but the effects of apex omnivores on ecosystems could be more varied because changes in the resource base alter their densities and reverberate through ecosystems in complex ways. In coastal temperate ecosystems throughout much of the Northern Hemisphere, anadromous salmon once supported abundant bear populations, but both taxa have declined or been extirpated from large parts of their former ranges with limited research on the consequences of diminished or absent interactions among species. Here we review the biogeography of bear-salmon interactions and the role of salmon-subsidized bears in (1) resource provisioning to plants and scavengers through the distribution of salmon carcasses, (2) competition among bears and other large carnivores, (3) predation of ungulate neonates, (4) seed dispersal, and (5) resource subsidies to rodents with seed-filled scats. In addition to our review of the literature, we present original data to demonstrate two community-level patterns that are currently unexplained. First, deer densities appear to be consistently higher on islands with abundant brown bears than adjacent islands with black bears and wolves, and moose calf survival is higher at low bear densities (<∼25 bears per 100 km2) but is constant across the vast majority of bear densities found in the wild (i.e., ∼>25 bears per 100 km2). Our review and empirical data highlight key knowledge gaps and research opportunities to understand the complex ecosystem effects related to bear-salmon interactions.

Stable Isotopes Reveal Variation in Consumption of Pacific Salmon by Brown Bears, Despite Ready Access in Small Streams

Brown bears Ursus arctos consume a wide range of organisms, including ungulates and plants, but Pacific salmon Oncorhynchus spp. are especially important to their diet where their ranges overlap. Although some brown bears minimize antagonistic encounters with other brown bears or infanticide by avoiding streams where salmon spawn, studies generally assume that brown bears with ready access to salmon feed heavily on them. To test this assumption, and the hypothesis that male brown bears would feed more heavily on salmon than females (owing to their sexual size dimorphism), we collected hair samples from brown bears by using barbed wire placed on six small tributaries of Lake Aleknagik, Alaska, USA, where adult Sockeye Salmon Oncorhynchus nerka are readily accessible and frequently consumed by brown bears. Analysis of DNA distinguished among the different brown bears leaving the hair samples, some of which were sampled multiple times within and among years. We assessed the contribution of salmon to the diet of individual brown bears by using carbon and nitrogen stable isotope signatures. The 77 samples analyzed from 31 different bears over 4 y showed isotopic ratios consistent with reliance on salmon, but the wide range of isotopic signatures included values suggesting variable, and in one case considerable, use of terrestrial resources. Stable isotope signatures did not differ between male and female brown bears, nor did they differ between two sides of the lake, despite marked differences in Sockeye Salmon density. We collected the hair samples when salmon were present, so there was some uncertainty regarding whether they reflected feeding during the current or previous season. Notwithstanding this caveat, the results are consistent with the hypothesis that salmon were sufficiently available to provide food for the brown bears and that the considerable isotopic variation among brown bears with access to salmon reflected their age, status, and behavior.

Losing seasonal patterns in a hibernating omnivore? Diet quality proxies and faecal cortisol metabolites in brown bears in areas with and without artificial feeding

Bears are omnivores particularly well-adapted to variations in the nutritional composition, quality and availability of food resources. Artificial feeding practices have been shown to strongly influence diet composition and seasonality, as well as to cause alterations in wintering and movement in brown bears (Ursus arctos). In this study, we investigated seasonal differences (hypophagia vs hyperphagia) in food quality of two brown bear subpopulations in the Polish Carpathians using faecal nitrogen (FN) and carbon (FC) estimates. The subpopulations inhabit areas that differ in artificial feeding practices: no artificial feeding occurs in the western subpopulation (Tatra Mountains), while artificial food targeted to ungulates is provided and used year-round in the eastern subpopulation (Bieszczady Mountains). We also compared these results with faecal cortisol metabolites (FCM) to explore how FN and FC correlate with the hypothalamic-pituitary-adrenal axis activity and if the seasonal patterns are apparent. We found that in Tatra Mts bears fed on significantly higher quality diet, as shown by FN and FC values, and had significantly higher FC levels in hyperphagia, when they accumulate fat reserves for wintering. The pattern in FCM levels for Tatra subpopulation followed the changes in energy intake during the seasons of hypo- and hyperphagia, while in Bieszczady Mts, the area with intensive feeding, no seasonal patterns could be observed. Artificial feeding practices may disrupt nutrient phenology and seasonality, relative to subpopulations with natural diets. We showed that the availability of human-provided foods may alter not only the overall dietary quality, but also hormonal patterns linked to seasonal nutritional requirements. Combining FN, FC and FCM proved to be a useful tool for reconstructing diet quality and related physiological patterns.

Dental Calculus as a Tool to Study the Evolution of the Mammalian Oral Microbiome

Dental calculus, the calcified form of the mammalian oral microbial plaque biofilm, is a rich source of oral microbiome, host, and dietary biomolecules and is well preserved in museum and archaeological specimens. Despite its wide presence in mammals, to date, dental calculus has primarily been used to study primate microbiome evolution. We establish dental calculus as a valuable tool for the study of nonhuman host microbiome evolution, by using shotgun metagenomics to characterize the taxonomic and functional composition of the oral microbiome in species as diverse as gorillas, bears, and reindeer. We detect oral pathogens in individuals with evidence of oral disease, assemble near-complete bacterial genomes from historical specimens, characterize antibiotic resistance genes, reconstruct components of the host diet, and recover host genetic profiles. Our work demonstrates that metagenomic analyses of dental calculus can be performed on a diverse range of mammalian species, which will allow the study of oral microbiome and pathogen evolution from a comparative perspective. As dental calculus is readily preserved through time, it can also facilitate the quantification of the impact of anthropogenic changes on wildlife and the environment.

Biogeographic problem-solving reveals the Late Pleistocene translocation of a short-faced bear to the California Channel Islands

An accurate understanding of biodiversity of the past is critical for contextualizing biodiversity patterns and trends in the present. Emerging techniques are refining our ability to decipher otherwise cryptic human-mediated species translocations across the Quaternary, yet these techniques are often used in isolation, rather than part of an interdisciplinary hypothesis-testing toolkit, limiting their scope and application. Here we illustrate the use of such an integrative approach and report the occurrence of North America's largest terrestrial mammalian carnivore, the short-faced bear, Arctodus simus, from Daisy Cave (CA-SMI-261), an important early human occupation site on the California Channel Islands. We identified the specimen by corroborating morphological, protein, and mitogenomic lines of evidence, and evaluated the potential natural and anthropogenic mechanisms of its transport and deposition. While representing just a single specimen, our combination of techniques opened a window into the behavior of an enigmatic species, suggesting that A. simus was a wide-ranging scavenger utilizing terrestrial and marine carcasses. This discovery highlights the utility of bridging archaeological and paleontological datasets to disentangle complex biogeographic scenarios and reveal unexpected biodiversity for island systems worldwide.

Dietary plasticity and the importance of salmon to brown bear (Ursus arctos) body size and condition in a low Arctic ecosystem

Ecological flexibility within animal populations can allow for variation in resource use and foraging decisions. We estimated brown bear (Ursus arctos) diet composition in Gates of the Arctic National Park and Preserve, Alaska from 2013 to 2015 to evaluate how variation in foraging behavior influences body condition and size. We used stable carbon (δ13C) and nitrogen (δ15N) isotope analyses of sectioned brown bear hair samples to evaluate assimilated diet. We then developed a set of a priori linear models to evaluate differences in the diet composition of brown bears (n = 80) in relation to body fat (%) and mass. The proportion of meat (salmon [Oncorhynchus keta] and terrestrial meat combined) in the diet from July through late September varied between male and female bears, with males ($$\stackrel{-}{x}$$ x - = 62%, SD = 30) assimilating significantly more meat than females ($$\stackrel{-}{x}$$ x - = 40%, SD = 29). Most of the meat consumed came from marine-derived resources for males (53% of the total diet or 86% of the meat) and females (31% of the total diet or 77% of the meat). As we found the range of observed diets was unrelated to physiological outcomes (i.e., percentage body fat), we suggest that ecological flexibility within populations may provide an adaptive advantage by allowing individuals to reduce competition with conspecifics by foraging on alternate food resources. Identifying variable foraging behaviors within a population can allow for a better understanding of complex behaviors and, ultimately, lead to more informed management decisions related to habitat use, development, and harvest.

Managing salmon for wildlife: Do fisheries limit salmon consumption by bears in small Alaskan streams?

Ecosystem-based management requires consideration of overlapping resource use between humans and other consumers. Pacific salmon are an important resource for both fisheries and populations of wildlife around the Pacific rim, including coastal brown bears (Ursus arctos); salmon consumption has been positively linked to bear density, body size, and reproductive rate. As a case study within the broader context of human-wildlife competition for food, we used 16-22 yr of empirical data in four different salmon-bearing systems in southwestern Alaska to explore the relationship between sockeye salmon (Oncorhynchus nerka) availability and consumption by bears. We found a negative relationship between the annual biomass of salmon available to bears and the fraction of biomass consumed per fish, and a saturating relationship between salmon availability and the total annual biomass of salmon consumed by bears. Under modeled scenarios, bear consumption of salmon was predicted to increase only with dramatic (on the order of 50-100%) increases in prey availability. Even such large increases in salmon abundance were estimated to produce relatively modest increases in per capita salmon consumption by bears (2.4-4.8 kg·bear^-1 ·d^-1 , 15-59% of the estimated daily maximum per capita intake), in part because bears did not consume salmon entirely, especially when salmon were most available. Thus, while bears catching salmon in small streams may be limited by salmon harvest in some years, current management of the systems we studied is sufficient for bear populations to reach maximum salmon consumption every 2-4 yr. Consequently, allocating more salmon for brown bear conservation would unlikely result in an ecologically significant response for bears in these systems, though other ecosystem components might benefit. Our results highlight the need for documenting empirical relationships between prey abundance and consumption, particularly in systems with partial consumption, when evaluating the ecological response of managing prey resources for wildlife populations.

Assessing dual hair sampling for isotopic studies of grizzly bears

RATIONALE

The stable isotope ratios of carbon (δ¹³ C values), nitrogen (δ¹⁵ N values) and sulfur (δ³⁴ S values) in bear hair can be used to obtain information on dietary history. Sample protocols often require hair sampling from multiple anatomical locations; however, there remains a question as to whether this is necessary for isotopic studies of hair. The purpose of this study was to determine whether significant differences can be observed for the δ¹³ C, δ¹⁵ N and δ³⁴ S values between paired hair samples taken from the rump and shoulder of grizzly bears (Ursus arctos).

METHODS

Paired hair samples were collected from the rump and the shoulder of 81 grizzly bears in the Yukon, Canada. Hair samples were analyzed using a thermal combustion elemental analyzer coupled with a continuous flow isotope ratio mass spectrometer.

RESULTS

Statistical comparisons of paired hair samples for both males and females showed no meaningful differences in δ¹³ C, δ¹⁵ N and δ³⁴ S values in hair taken from the rump and shoulder, and any observed differences fell within the instrumental error.

CONCLUSIONS

Based on these results, hair may be safely sampled on either the rump or the shoulder without loss of isotopic information and thus this finding allows for refinement of sampling.

The effect of sex, age, and location on carnivory in Utah black bears (Ursus americanus)

Ungulates are important to the diet of bears because they are high in protein, and the level of dietary protein strongly influences bear size. The size a bear obtains as an adult influences important life history characteristics, such as age of reproduction and reproductive success; therefore, it is important to know what foods are available to bears and how they are utilizing them. We tested hypotheses concerning the effect of age, sex, and location on black bear carnivory. We collected hair and vestigial premolar teeth from 49 Utah black bears, Ursus americanus according to the Utah Division of Wildlife Resources hunt unit. Hunt units differed in habitat quality and local ungulate density. We analyzed a vestigial premolar for the age of the bears and used analysis of the δ¹³C and δ¹⁵N values of the hairs of each bear to infer the degree of carnivory. δ¹⁵N of black bear hairs was positively correlated with increased availability of ungulates. There was a positive relationship between the δ¹⁵N of bear hairs and age in hunt units with the highest ungulate densities only. The δ¹⁵N and δ¹³C of black bear hairs were positively correlated, suggesting that bears are more carnivorous at higher altitudes. This study demonstrates the value of stable isotope analysis in understanding the feeding ecology of bears over broad geographic ranges. It demonstrates that ungulate availability is important to the feeding ecology of black bears in the Intermountain West.

EXPOSURE OF ALASKA BROWN BEARS (URSUS ARCTOS) TO BACTERIAL, VIRAL, AND PARASITIC AGENTS VARIES SPATIOTEMPORALLY AND MAY BE INFLUENCED BY AGE

We collected blood and serum from 155 brown bears (Ursus arctos) inhabiting five locations in Alaska, US during 2013-16 and tested samples for evidence of prior exposure to a suite of bacterial, viral, and parasitic agents. Antibody seroprevalence among Alaska brown bears was estimated to be 15% for Brucella spp., 10% for Francisella tularensis, 7% for Leptospira spp., 18% for canine adenovirus type 1 (CAV-1), 5% for canine distemper virus (CDV), 5% for canine parvovirus, 5% for influenza A virus (IAV), and 44% for Toxoplasma gondii. No samples were seropositive for antibodies to Trichinella spp. Point estimates of prior exposure to pathogens among brown bears at previously unsampled locations generally fell within the range of estimates for previously or contemporaneously sampled bears in Alaska. Statistical support was found for variation in antibody seroprevalence among bears by location or age cohort for CAV-1, CDV, IAV, and T. gondii. There was limited concordance in comparisons between our results and previous serosurveys regarding spatial and age-related trends in antibody seroprevalence among Alaska brown bears suggestive of temporal variation. However, we found evidence that the seroprevalence of CAV-1 antibodies is consistently high in bears inhabiting southwest Alaska and the cumulative probability of exposure may increase with age. We found evidence for seroconversion or seroreversion to six different infectious agents in one or more bears. Results of this study increase our collective understanding of disease risk to both Alaska brown bear populations and humans that utilize this resource.

Phenological tracking associated with increased salmon consumption by brown bears

There is growing interest in the ecological significance of phenological diversity, particularly in how spatially variable resource phenologies (i.e. resource waves) prolong foraging opportunities for mobile consumers. While there is accumulating evidence of consumers moving across landscapes to surf resource waves, there is little data quantifying how phenological tracking influences resource consumption due to the challenge of documenting all the components of this ecological phenomenon (i.e., phenological variation, consumer movement, resource consumption, and consumer fitness). We examined the space use of GPS collared female brown bears to quantify the exploitation of a salmon resource wave by individual bears. We then estimated salmon consumption levels in the same individuals using stable isotope and mercury analyses of hair. We found strong positive relationships between time spent on salmon streams and percent salmon in assimilated diets (R² = 0.70) and salmon mass consumed (R² = 0.49). Salmon abundance varied 2.5-fold between study years, yet accounting for salmon abundance did not improve salmon consumption models. Resource abundance generally is viewed as the key variable controlling consumption levels and food web dynamics. However, our results suggest that in intact watersheds of coastal Alaska with abundant salmon runs, interannual variation in salmon abundance likely has less effect on salmon consumption than individual variation in bear foraging behavior. The results complement previous work to demonstrate the importance of phenological variation on bear foraging behavior and fitness.

Using multiple data types and integrated population models to improve our knowledge of apex predator population dynamics

Current management of large carnivores is informed using a variety of parameters, methods, and metrics; however, these data are typically considered independently. Sharing information among data types based on the underlying ecological, and recognizing observation biases, can improve estimation of individual and global parameters. We present a general integrated population model (IPM), specifically designed for brown bears (Ursus arctos), using three common data types for bear (U. spp.) populations: repeated counts, capture–mark–recapture, and litter size. We considered factors affecting ecological and observation processes for these data. We assessed the practicality of this approach on a simulated population and compared estimates from our model to values used for simulation and results from count data only. We then present a practical application of this general approach adapted to the constraints of a case study using historical data available for brown bears on Kodiak Island, Alaska, USA. The IPM provided more accurate and precise estimates than models accounting for repeated count data only, with credible intervals including the true population 94% and 5% of the time, respectively. For the Kodiak population, we estimated annual average litter size (within one year after birth) to vary between 0.45 [95% credible interval: 0.43; 0.55] and 1.59 [1.55; 1.82]. We detected a positive relationship between salmon availability and adult survival, with survival probabilities greater for females than males. Survival probabilities increased from cubs to yearlings to dependent young ≥2 years old and decreased with litter size. Linking multiple information sources based on ecological and observation mechanisms can provide more accurate and precise estimates, to better inform management. IPMs can also reduce data collection efforts by sharing information among agencies and management units. Our approach responds to an increasing need in bear populations’ management and can be readily adapted to other large carnivores.

An assessment of the efficacy of rub stations for detection and abundance surveys of Canada lynx (Lynx canadensis)

Barbed and scented rub pads that rely on a cheek-rubbing behavioural response are a standard survey design that has been used extensively across the range of Canada lynx (Lynx canadensis Kerr, 1792). However, there have not been any published studies evaluating the effectiveness of rub stations for detecting lynx by comparing other simultaneous survey methods. We used a combination of paired rub stations and remote cameras at 41 sites to compare detection probabilities between the two methods and conduct a mark–recapture population estimate of Canada lynx using rub stations to further interpret our findings. The detection probability calculated using cameras approached 1.0 for most of the winter season (mean = 0.88), whereas it remained less than 0.52 for hair rub stations (mean = 0.27). The low and variable detection probability using hair snags, high detection probability using cameras, and the potential gender or individual bias in rubbing behaviour based on our mark–recapture analysis suggest that rub stations are not the most efficient survey method available for Canada lynx. Until additional research incorporating spatial scale, seasonal timing, gender bias, and survey design is conducted, we urge caution in the use of hair stations that rely on the cheek-rubbing behaviour of Canada lynx.

Dietary niche partitioning among black bears, grizzly bears, and wolves in a multiprey ecosystem

Identifying mechanisms that promote coexistence of sympatric species is important for predicting ecological effects of anthropogenic change. Many caribou (Rangifer tarandus (L., 1758)) populations are declining, and it is unclear to what extent sympatric predators consume caribou or how alternative prey affect caribou–predator relationships. We used stable isotope mixing models to estimate diets of black bear (Ursus americanus Pallas, 1780), grizzly bear (Ursus arctos L., 1758), and grey wolves (Canis lupus L., 1758) during early, middle, and late summer of 2009–2010 in northwestern British Columbia, Canada. Although we expected wolf diet to be primarily composed of moose (Alces alces (L., 1758)) — as they exist at twice the density of caribou — wolf diet consisted principally of caribou, and to a lesser extent moose and beaver (Castor canadensis Kuhl, 1820), with little change occurring throughout summer. Black bear diet consisted mainly of vegetation and moose, shifting from moose to vegetation through summer. Grizzly bear diet consisted primarily of vegetation and moose, and did not change throughout summer. Our results demonstrate the role of dietary niche partitioning in bear and wolf coexistence, and that caribou may be primary prey for wolves in an ecosystem with relatively high moose abundance and low human development.

Pathology, clinical signs, and tissue distribution of Toxoplasma gondii in experimentally infected reindeer (Rangifer tarandus)

Toxoplasma gondii is a zoonotic parasite found in vertebrates worldwide for which felids serve as definitive hosts. Despite low densities of felids in northern Canada, Inuit people in some regions show unexpectedly high levels of exposure, possibly through handling and consumption of Arctic wildlife. Free-ranging caribou (Rangifer tarandus) are widely harvested for food across the Canadian North, show evidence of seroexposure to T. gondii, and are currently declining in numbers throughout the Arctic. We experimentally infected three captive reindeer (conspecific with caribou) with 1000, 5000 or 10,000 oocysts of T. gondii via stomach intubation to assess clinical signs of infection, pathology, and tissue distribution. An unexposed reindeer served as a negative control. Signs of stress, aggression, and depression were noted for the first two weeks following infection. By 4 weeks post infection, all infected reindeer were positive on a modified agglutination test at the highest titer tested (1:200) for antibodies to T. gondii. At 20 weeks post infection, no gross abnormalities were observed on necropsy. Following histopathology and immunohistochemistry, tissue cysts were visualized in the reindeer given the highest and lowest dose of oocysts. Focal pleuritis and alveolitis were associated with respiratory problems in reindeer given the middle dose. DNA of T. gondii was detected following traditional DNA extraction and conventional PCR on 25 mg samples from 17/33 muscles and organs, and by magnetic capture DNA extraction from 100 g samples from all 26 tissues examined. This research demonstrated that reindeer/caribou can serve as intermediate hosts for T. gondii, and that the parasite may be associated with health effects in wildlife. The presence of T. gondii in all tissues tested, many of which are commonly consumed raw, smoked, or dried in northern communities, suggests that caribou may serve as a source of human exposure to T. gondii.

Dental and Temporomandibular Joint Pathology of the North American Brown Bear (Ursus arctos horribilis, Ursus arctos middendorffi and Ursus arctos sitkensis)

Museum specimens (maxillae and mandibles) from 393 North American brown bears (Ursus arctos) from Alaska were examined macroscopically according to predefined criteria and 204 specimens were included in this study. The specimens were acquired between 1905 and 2012. There were 99 specimens (48.5%) from male animals, 87 (42.7%) from female animals and 18 (8.8%) from animals of unknown sex. The ages of the animals ranged from neonate to adult, with 92 adults (45.1%) and 112 young adults (54.9%) included and neonates/juveniles excluded from the study. The number of teeth available for examination was 6,525 (76.2%); 8.6% of teeth were absent artefactually, 0.8% were deemed absent due to acquired tooth loss and 14.5% were absent congenitally. None of the brown bears had supernumerary teeth, persistent deciduous teeth or abnormally formed crowns. Only four of the specimens in the present population were affected by enamel hypoplasia and one specimen contained two mandibular fourth premolar teeth with one root instead of two. All 204 specimens displayed at least some degree of attrition/abrasion, affecting 63% of all teeth, ranging from mild wear of the enamel to deep abrasion associated with pulp exposure. Ten-times more adult than young adult specimens had abrasion causing pulp exposure, while more young adults showed mild attrition/abrasion. Dental fractures were noted in one-third of brown bears and in 3.0% of the total number of present teeth. More adult brown bears had dental fractures than young adults. There were 11 specimens (5.4%) that displayed overt periapical disease, affecting a total of 20 dental alveoli (0.22%), with adults significantly more affected than young adults. Some degree of periodontitis was seen in 145 specimens (71.1%), affecting 13.6% of all dental alveoli. Nearly one-third (29.9%) of skulls displayed skeletal and/or dental malocclusion, most commonly a level bite. Lesions consistent with temporomandibular joint (TMJ) osteoarthritis were found in 27 specimens (13.2%). Caries lesions were discovered in four specimens (2.0%), affecting eight teeth in total. Although the clinical significance of dental and TMJ pathology in the brown bear remains elusive, the occurrence and severity of some of these lesions may play an important role in the morbidity of this species.