Caribou Populations Research Articles

Birth date determines early calf survival in migratory caribou.

The decline of most caribou (Rangifer tarandus) populations underlines the need to understand the determinants of key demographic parameters. In migratory caribou, we have limited information on rates and drivers of pre-weaning mortality. We fitted 60 pregnant females of the Rivière-aux-Feuilles caribou herd with GPS camera collars to track the survival of calves from birth to weaning in 2016-2018. Over the three years, calf survival rate before weaning, i.e. to 01-Sep, approximately three months of age, was 0.63 (CI 0.50-0.77). Summer mortality risk was mainly influenced by calf birth date, with calves born earlier in the calving season having a lower mortality risk than those born later. Mortality also increased when calves experienced low or high temperature during calving. This study provides the first estimates of pre-weaning survival of migratory caribou calves in this herd, illustrating the value of new technologies to collect data otherwise difficult to obtain in widely distributed migratory populations. This approach can easily be extended to other large herbivores and predators. Our study brings new insights on how climate change may affect summer juvenile survival given the increased temperatures and faster changes in plant phenology expected in the future.

Public opinion on the conflict between the conservation of at-risk species and the extraction of natural resources: The case of caribou in boreal forest

Conflicts between economic development and conservation are increasingly hampering efforts to restore imperiled wildlife populations. Public opinion can influence how these conflicts translate into conservation actions, encouraging stakeholders to express their views through various public channels. The outcome of these campaigns typically remains unknown. Via an online survey, we collected to the opinion of 1000 citizens of Québec, Canada, regarding the ongoing conflict between logging and the conservation of at-risk caribou populations (Rangifer tarandus). We found that people expect conservation actions that are sufficient to recover caribou populations, even if millions of government investment are required and jobs are lost in the process. When respondents learned that academic caribou researchers indicated that the two management strategies being studied by government would be insufficient for population recovery, one-third withdrew their support for either strategy. Age, gender and education all explain variation in public opinion, but it was the region of residence that most consistently explained variation in opinion. Residents of caribou-inhabited regions were less concerned about caribou conservation and more supportive of forestry than residents of other regions, reflecting regional differences in expected economic impacts of conservation, not negative interactions with caribou. In fact, most people supported strong conservation actions for the recovery of caribou populations, regardless of their socio-demographics. Our analysis provides general insights into how public opinion on the trade-off between conservation and economy is influenced by socio-demographics and scientific conclusions. We found that current government conservation actions (or lack thereof) are not in line with mainstream public opinion. Moreover, we show that making species at-risk lists does not ensure that the species will benefit from strong conservation actions without lengthy delays, even for a high-profile, flagship species like caribou. This observation echoes concerns about the fate of less charismatic, at-risk species, and thus about future biodiversity conservation efforts.

In search of evidence-based management targets: A synthesis of the effects of linear features on woodland caribou

Effective species management relies on evidence-based goals that address the processes influencing population demography. These goals therefore require understanding how stressors affect the species of interest, and the food web within which the focal species is embedded. For woodland caribou, a conservation priority across much of its range, habitat loss and alteration is a primary cause of decline. Governments have identified maximum disturbance targets whereby a maximum of 35% total disturbance provides a 60% likelihood of self-sustaining caribou populations, but targets specific for linear features such as roads and seismic lines — which play a key role in altering ecological processes and are a primary focus for habitat restoration — have not been established. We created a framework to conceptually link stressors (linear features) to caribou declines via ecological mechanisms, and used this framework to guide a literature review to support the development of a linear feature-based management target for Southern Mountain Caribou. Despite the vast amount of research investigating the mechanisms leading to the negative relationship between caribou demography and linear features, our review of 54 peer-reviewed manuscripts and 99 grey-literature reports found little to no evidence of a threshold in these relationships in which to inform a linear feature-based management target for caribou population growth. Most studies evaluated how linear features modify space use of caribou, their predators, and the primary prey of those predators, whereas few mechanistically linked linear features to caribou demography. Our work provides a foundation in which other systems can conceptualize how stressors are linked to species declines, and to support the development of evidence-based management goals.

Genomics of founders for conservation breeding: the Jasper caribou case.

The online version contains supplementary material available at 10.1007/s10592-023-01540-3.

Applying remote sensing for large‐landscape problems: Inventorying and tracking habitat recovery for a broadly distributed Species At Risk

Abstract Anthropogenic habitat alteration is leading to the reduction of global biodiversity. Consequently, there is an imminent need to understand the state and trend of habitat alteration across broad areas. In North America, habitat alteration has been linked to the decline of threatened woodland caribou. As such, habitat protection and restoration are critical measures to support recovery of self‐sustaining caribou populations. Broad estimates of habitat change through time have set the stage for understanding the status of caribou habitat. However, the lack of updated and detailed data on post‐disturbance vegetation recovery is an impediment to recovery planning and monitoring restoration effectiveness. Advances in remote sensing tools to collect high‐resolution data at large spatial scales are beginning to enable ecological studies in new ways to support ecosystem‐based and species‐based management. We used semi‐automated and manual methodologies to fuse photogrammetry point clouds (PPC) from high‐resolution aerial imagery with wide‐area light detection and ranging (LiDAR) data to quantify vegetation structure (height, density, class) on disturbances associated with caribou declines. We also compared vegetation heights estimated from the semi‐automated PPC‐LiDAR fusion to heights estimated in the field, using stereoscopic interpretation, and using multi‐channel TiTAN LiDAR. Vegetation regrowth was occurring on many of the disturbance types, though there was local variability in the type, height and density of vegetation. Heights estimated using PPC‐LiDAR fusion were highly correlated (r ≥ 0.87 in all cases) with heights estimated using stereomodels, TiTAN multi‐channel LiDAR and field measurements. We demonstrated that PPC‐LiDAR fusion can be operationalized over large areas to collect comprehensive and consistent vegetation data across landscape levels, providing opportunities to link fine‐resolution remote sensing to landscape‐scale ecological studies. Crucially, these data can be used to estimate rates of habitat recovery at resolutions that are not feasible using more commonly used satellite‐based sensors, bridging the gap between resolution and extent. Such data are needed to achieve effective and efficient habitat monitoring to support caribou recovery efforts, as well as a myriad of additional forest management needs.

Genomic population structure and inbreeding history of Lake Superior caribou.

Caribou (Rangifer tarandus) have experienced dramatic declines in both range and population size across Canada over the past century. Boreal caribou (R. t. caribou), 1 of the 12 Designatable Units, has lost approximately half of its historic range in the last 150 years, particularly along the southern edge of its distribution. Despite this overall northward contraction, some populations have persisted at the trailing range edge, over 150 km south of the continuous boreal caribou range in Ontario, along the coast and nearshore islands of Lake Superior. The population history of caribou along Lake Superior remains unclear. It appears that these caribou likely represent a remnant distribution at the trailing edge of the receding population of boreal caribou, but they may also exhibit local adaptation to the coastal environment. A better understanding of the population structure and history of caribou along Lake Superior is important for their conservation and management. Here, we use high-coverage whole genomes (N = 20) from boreal, eastern migratory, and barren-ground caribou sampled in Manitoba, Ontario, and Quebec to investigate population structure and inbreeding histories. We discovered that caribou from the Lake Superior range form a distinct group but also found some evidence of gene flow with the continuous boreal caribou range. Notably, caribou along Lake Superior demonstrated relatively high levels of inbreeding (measured as runs of homozygosity; ROH) and genetic drift, which may contribute to the differentiation observed between ranges. Despite inbreeding, caribou along Lake Superior retained high heterozygosity, particularly in genomic regions without ROH. These results suggest that they present distinct genomic characteristics but also some level of gene flow with the continuous range. Our study provides key insights into the genomics of the southernmost range of caribou in Ontario, beginning to unravel the evolutionary history of these small, isolated caribou populations.

Incorporating mechanism into conservation actions in an age of multiple and emerging threats: The case of boreal caribou

AbstractConservation strategies for imperiled species are frequently based on identifying and addressing the probable causes of population decline, an approach known as the declining population paradigm. Causes, however, are frequently linked to demographic outcomes by multiple mechanisms, and failing to target the primary mechanisms can reduce the effectiveness and efficiency of conservation actions. Increasingly, conservation strategies also need to consider emerging threats, such as climate change. Here, we use boreal caribou (Rangifer tarandus caribou), a threatened ecotype of woodland caribou, as a case study to illustrate how landscape disturbance and climate change can each exert negative demographic effects on caribou through multiple and complex mechanisms. We reviewed the extensive literature focused on woodland caribou to identify and assess the relative importance of each putative mechanism. While disturbance‐mediated apparent competition, the expansion of novel predators, and altered predator behavior appear to be primary mechanisms dictating past and current declines of caribou, climate change has increasing potential to exert strong direct and indirect effects now and in the future. Predicted climate effects may prevent some populations from regaining self‐sustaining status, despite local conservation actions. Our review revealed several knowledge gaps, notably a lack of clarity on the spatial extent of undisturbed habitat required for caribou populations to be stable. We used outcomes from our review to demonstrate how a mechanistic understanding of population decline can inform habitat‐based conservation strategies for caribou. For populations residing within highly disturbed ranges, habitat restoration is a key recommendation of current conservation strategies, yet the large spatial extent of disturbances will require prioritization of areas for restoration. Maximizing the conservation return‐on‐investment for caribou will require a mechanistically informed prioritization process that targets conservation actions toward the primary mechanisms underlying population decline.

Will this umbrella leak? A caribou umbrella index for boreal landbird conservation

AbstractConservation approaches that efficiently protect multiple values, such as the umbrella species concept, have been widely promoted with expected dramatic ecosystem changes. Due to its social and cultural importance, and recent declining trends, boreal populations of woodland caribou have been suggested as potential umbrella species for other declining taxa, such as boreal landbirds. We propose a generic pixel‐based umbrella index that focuses on fine‐grained habitat overlaps. In light of ongoing conservation efforts worldwide implementing area‐based targets (e.g., 30% by 2030), we used a random neutral model as baseline, as opposed to a no‐conservation scenario, which has been used elsewhere. We found that the conservation efficiency of caribou as an umbrella for 71 co‐occurring landbirds—three of which are priority species—in the Northwest Territories, Canada, is generally lower than our random model, as 53% of the species presented negative umbrella index medians with the interquartile range not overlapping zero. We conclude that in cases where area‐based targets drive decision‐making and the issue at stake involves identifying which areas to conserve—not whether to conserve—woodland caribou may be a leaky umbrella for most co‐occurring landbird species and these might need complementary conservation actions to be brought in from the rain.

Climate-informed forecasts reveal dramatic local habitat shifts and population uncertainty for northern boreal caribou.

Most research on boreal populations of woodland caribou (Rangifer tarandus caribou) has been conducted in areas of high anthropogenic disturbance. However, a large portion of the species' range overlaps relatively pristine areas primarily affected by natural disturbances, such as wildfire. Climate-driven habitat change is a key concern for the conservation of boreal-dependent species, where management decisions have yet to consider knowledge from multiple ecological domains integrated into a cohesive and spatially explicit forecast of species-specific habitat and demography. We used a novel ecological forecasting framework to provide climate-sensitive projections of habitat and demography for five boreal caribou monitoring areas within the Northwest Territories (NWT), Canada, over 90 years. Importantly, we quantify uncertainty around forecasted mean values. Our results suggest habitat suitability may increase in central and southwest regions of the NWT's Taiga Plains ecozone but decrease in southern and northwestern regions driven by conversion of coniferous to deciduous forests. We do not project that boreal caribou population growth rates will change despite forecasted changes to habitat suitability. Our results emphasize the importance of efforts to protect and restore northern boreal caribou habitat despite climate uncertainty while highlighting expected spatial variations that are important considerations for local people who rely on them. An ability to reproduce previous work, and critical thought when incorporating sources of uncertainty, will be important to refine forecasts, derive management decisions, and improve conservation efficacy for northern species at risk.

Global change risks a threatened species due to alteration of predator–prey dynamics

AbstractAlthough global change can reshape ecosystems by triggering cascading effects on food webs, indirect interactions remain largely overlooked. Climate‐ and land‐use‐induced changes in landscape cause shifts in vegetation composition, which affect entire food webs. We used simulations of forest dynamics and movements of interacting species, parameterized by empirical observations, to predict the outcomes of global change on a large‐mammal food web in the boreal forest. We demonstrate that climate‐ and land‐use‐induced changes in forest landscapes exacerbate asymmetrical apparent competition between moose and threatened caribou populations through wolf predation. Although increased prey mortalities came from both behavioral and numerical responses, indirect effects from numerical responses had an overwhelming effect. The increase in caribou mortalities was exacerbated by the cumulating effects of land use over the short term and climate change impacts over the long term, with higher impact of land use. Indirect trophic interactions will be key to understanding community dynamics under global change.

Where to begin? A flexible framework to prioritize caribou habitat restoration

Habitat loss is a leading threat to many species at risk, and as such, the need for habitat restoration is widespread. In the boreal forests of Western Canada, habitat restoration is a key habitat management action needed to achieve self‐sustaining populations of woodland caribou, a federally threatened species in decline. Hundreds of thousands of kilometers of linear features were created during the exploration or extraction of oil and gas that are no longer used, yet natural regeneration remains stagnated. Only a fraction of these linear features is restored each year, sparking the need for managers to prioritize efforts. We developed an algorithm to prioritize habitat restoration and demonstrate how it can be used to predict and monitor progress towards restoration goals. Our approach is based on the idea of maximizing the gain in unaltered caribou habitat per unit cost, while allowing for the inclusion of different goals, costs, and weighting criteria. Our algorithm ranked landscape units into five zones of restoration priority. The largest gain in unaltered habitat occurred following restoration of the highest priority zones, with diminishing returns as restoration proceeded. None of the caribou ranges reached habitat management targets when not considering restoration within energy project boundaries, even after all candidate linear features were restored. Our results highlight the need for ambitious, coordinated restoration, and the need for improved land‐use planning to minimize alteration within caribou range. We demonstrate the flexibility of our algorithm by applying the framework to a case study in a mountain ecosystem.

Life history matters: Differential effects of abomasal parasites on caribou fitness

Parasites can impact wildlife populations through their effects on host fitness and survival. The life history strategies of a parasite species can dictate the mechanisms and timing through which it influences the host. However, unravelling this species-specific effect is difficult as parasites generally occur as part of a broader community of co-infecting parasites. Here, we use a unique study system to explore how life histories of different abomasal nematode species may influence host fitness. We examined abomasal nematodes in two adjacent, but isolated, West Greenland caribou (Rangifer tarandus groenlandicus) populations. One herd of caribou were naturally infected with Ostertagia gruehneri, a common and dominant summer nematode of Rangifer sspp., and the other with Marshallagia marshalli (abundant; winter) and Teladorsagia boreoarcticus (less abundant; summer), allowing us to determine if these nematode species have differing effects on host fitness. Using a Partial Least Squares Path Modelling approach, we found that in the caribou infected with O. gruehneri, higher infection intensity was associated with lower body condition, and that animals with lower body condition were less likely to be pregnant. In caribou infected with M. marshalli and T. boreoarcticus, we found that only M. marshalli infection intensity was negatively related to body condition and pregnancy, but that caribou with a calf at heel were more likely to have higher infection intensities of both nematode species. The differing effects of abomasal nematode species on caribou health outcomes in these herds may be due to parasite species-specific seasonal patterns which influence both transmission dynamics and when the parasites have the greatest impact on host condition. These results highlight the importance of considering parasite life history when testing associations between parasitic infection and host fitness.

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

AbstractThe 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.

Evaluating the impact of caribou habitat restorationon predator and prey movement.

Fragmentation of the boreal forest by linear features, including seismic lines, has destabilized predator-prey dynamics, resulting in the decline of woodland caribou (Rangifer tarandus caribou) populations. Restoration of human-altered habitat has therefore been identified as a critical management tool for achieving self-sustaining woodland caribou populations. However, only recently has testing of the response of caribou and other wildlife to restoration activities been conducted. Early work has centered around assessing changes in wildlife use of restored seismic lines. We evaluated whether restoration reduces the movement rates of predators and their associated prey, which is expected to decrease predator hunting efficiency and ultimately reduce caribou mortality. We developed a new method for using cameras to measure fine-scale movement by measuring speed as animals traveled between cameras in an array. We used our method to quantify speed of caribou, moose (Alces alces), bears (Ursus americanus), and wolves (Canis lupus) on treated (restored) and untreated seismic lines. Restoration treatments reduced travel speeds along seismic lines of wolves by 1.38km/h, bears by 0.55km/h, and caribou by 1.57km/h, but did not reduce moose travel speeds. Reduced predator and caribou speeds on treated seismic lines are predicted to decrease encounter rates between predators and caribou and thus lower caribou kill rates. However, further work is needed to determine whether reduced movement rates result in reduced encounter rates with prey, and ultimately reduced caribou mortality.

Investigating potential for competition between migratory caribou and introduced muskoxen

AbstractSeveral caribou (Rangifer tarandus) populations co‐occur with endemic or introduced populations of muskoxen (Ovibos moschatus), which has led to concerns about the potential competition between the species, especially in regions where the growth of muskoxen populations coincides with caribou declines. We evaluated the potential for competition between migratory caribou and an introduced muskoxen population in northern Québec, Canada, at multiple spatial scales, from 2017 to 2019. We investigated space use and habitat selection patterns of satellite‐collared caribou and muskoxen, and analyzed fecal samples using DNA metabarcoding to assess diet overlap. Annual overlap between ranges was low and occurred primarily during caribou spring migrations on the coast of Hudson Bay, and during summer on the coast of Ungava Bay. During spring, muskoxen selected shrub‐dominated areas close to the coast, whereas caribou selected rock‐substrate tundra and low elevations within their overlapping ranges. Thus, co‐occurrence was low and remained limited to the vicinity of the Hudson Bay. In summer, muskoxen selected productive coastal areas and caribou selected erect‐shrub tundra; both species selected prostrate‐shrub tundra. This led to a higher co‐occurrence in the Ungava Bay study area relative to the Hudson Bay study area. We found similarities in the diets of the 2 species at the plant family level, with shrubs being commonly consumed by both species across seasons. We conclude that, at a broad spatial scale, there was limited potential for seasonal space use and diet overlap between caribou and muskoxen in our study area. Still, multiple sources of uncertainty remain such as local impacts of herbivory by muskoxen, demographic and distribution patterns of both species, trophic interactions with predators, shared diseases and parasites, and climate change. These sources of uncertainty could be mitigated through the elaboration of local management plans and community‐based monitoring.

Nested population structure of threatened boreal caribou revealed by network analysis

Delineating relevant local populations of widely distributed species is a common challenge in conservation ecology. Caribou and reindeer (Rangifer tarandus) are in general decline throughout their global range, despite ongoing conservation efforts. In Canada, recovery actions for the threatened boreal population of woodland caribou (Rangifer tarandus caribou) are stratified by ‘local population units’ (LPUs) on ranges distributed across 2.4 × 10 km2 of the species’ geographic range. To estimate local population dynamics, LPUs are assumed to be geographically closed, though supporting evidence varies widely. We assembled an exceptionally large database of GPS telemetry locations (891,306 telemetry days, 1998–2020) from 1586 adult female caribou across the 19 northwesternmost LPUs. We generated a many-to-many Gaussian Bayesian Network to identify candidate local populations at range-level extents, as well as subpopulations, termed ‘communities’ in network analysis. We detected local population boundaries that in some cases were consistent with accepted LPUs and consistent with the assumption of geographic closure. In other cases, local population boundaries did not map well to currently delineated LPUs. Several communities at smaller spatial extents were consistent with expert and local knowledge of caribou movements and support recovery planning and actions “stepped down” from entire ranges. Evidence consistent with population fragmentation was confirmed along the southern and southwestern boundaries of the species’ geographic range within the study area, as were more continuous distributions confirmed to the north. We suggest that network analysis can help to inform conservation planning for boreal caribou and other wide-ranging species that would benefit from data-driven characterizations of multiscale population spatial structure.

There is still time to reconcile forest management with climate-driven declines in habitat suitability for boreal caribou

Many boreal populations of woodland caribou in Canada are declining, mainly due to the prevalence of anthropogenic disturbances which alter predator-prey dynamics. Climate change is expected to exert an additional negative influence on caribou populations in coming decades, but it is unclear whether or how human activities and climate change will interact to influence habitat suitability for caribou, and how important these agents of change will be relative to each other. In this study, we used the LANDIS-II forest landscape model to forecast boreal caribou habitat suitability across its distribution within the harvestable boreal forest in Québec for the period 2020–2100, under three increasing anthropogenic radiative forcing scenarios (baseline, Representative Concentration Pathways [RCP] 4.5 and 8.5), and two contrasting harvest scenarios (with and without harvest). Our simulations revealed that harvesting was the dominant agent explaining future variations in caribou habitat suitability, although climate change also decreased habitat suitability, especially under RCP 8.5. Climate-induced decreases in habitat suitability mostly originated from increases in wildfires that burned mature conifer-dominated forests, i.e., high-quality habitat for caribou. Habitat suitability by 2100 was also predicted to vary spatially, with the northeastern and northwestern parts of the study area supporting better caribou habitat conditions regardless of scenarios. We show that reducing harvest activities in areas where habitat suitability is currently high could help maintain high-quality caribou habitat even under the most intense climate change scenario. Our results also suggest that highly-disturbed regions which currently provide low-quality habitat may not improve in the future unless active habitat restoration is performed. Our study helps disentangle the potential future effects of forest management and climate change as threats to caribou habitat, emphasizing the urgency of reconciling forest management with the conservation of this species at risk in Canada.

Demographic history and conservation genomics of caribou (Rangifer tarandus) in Québec.

The loss of genetic diversity is a challenge many species are facing, with genomics being a potential tool to inform and prioritize decision-making. Most caribou (Rangifer tarandus) populations have experienced significant recent declines throughout Québec, Canada, and are considered of concern, threatened or endangered. Here, we calculated the ancestral and contemporary patterns of genomic diversity of five representative caribou populations and applied a comparative population genomics framework to assess the interplay between demographic events and genomic diversity. We first calculated a caribou specific mutation rate, μ, by extracting orthologous genes from related ungulates and estimating the rate of synonymous mutations. Whole genome re-sequencing was then completed on 67 caribou: from these data we calculated nucleotide diversity, θ π and estimated the coalescent or ancestral effective population size (N e), which ranged from 12,030 to 15,513. When compared to the census size, N C, the endangered Gaspésie Mountain caribou population had the highest ancestral N e:N C ratio which is consistent with recent work suggesting high ancestral N e:N C is of conservation concern. In contrast, values of contemporary N e, estimated from linkage-disequilibrium, ranged from 11 to 162, with Gaspésie having among the highest contemporary N e:N C ratio. Importantly, classic conservation genetics theory would predict this population to be of less concern based on this ratio. Interestingly, F varied only slightly between populations, and despite evidence of bottlenecks across the province, runs of homozygosity were not abundant in the genome. Tajima's D estimates mirrored the demographic models and current conservation status. Our study highlights how genomic patterns are nuanced and potentially misleading if viewed only through a contemporary lens; we argue a holistic conservation genomics view should integrate ancestral N e and Tajima's D into management decisions.

Stable isotopes indicate reduced body condition of caribou in disturbed areas

Abstract Understanding the impacts of disturbance on individual fitness is important for wildlife management, and critical for the conservation of species at risk. We compared the fitness and seasonal range use of 39 woodland caribou in Ontario study areas contrasted by their level of human disturbance. We previously showed that wolf density in the disturbed site was higher, likely due to human-modified landscapes favoring moose, the primary prey of wolves. In this paper we address three objectives. First, because the assimilation of dietary nitrogen is heavily influenced by metabolic processes related to stress, we hypothesized that ratios of nitrogen isotopes (N) may indicate changes in body condition in ungulates and be useful proxies for changes in fitness. Second, we predicted that increased predation risk from wolves in disturbed areas would result in measurable declines in caribou body condition. Third, we hypothesized that one mechanism for fitness declines among caribou in the disturbed area was increased wolf activity restricting caribou seasonal movements. We showed change in N in the tissues of caribou was correlated with body condition scoring using fat assessment. We used GPS collars to quantify seasonal range use and found that fitness was higher, and seasonal range overlap was lower, in caribou using the nondisturbed area. Winter fitness declines were significantly larger in the more disturbed area. Our study identifies another mechanism by which the cumulative effects of human-disturbed landscapes on caribou fitness could contribute to global declines in caribou populations.

Links between individual performance, trace elements and stable isotopes in an endangered caribou population

Foraging is a key behaviour, and several aspects of foraging remain to be investigated in many wild species. Low energy gain or reduced protein, nutrient, and mineral intake may explain poor individual condition, low reproductive output, high mortality, and, in extreme cases, population declines. Our study explores how foraging ecology, diet composition, and nutritional status could influence individual performance in an endangered population of caribou (Rangifer tarandus caribou). We measured stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) as well as the concentration of 21 trace elements in hairs of 44 caribou (~ 50% of the population). Our results showed that the Atlantic-Gaspésie caribou population consumed mainly lichens, horsetails, deciduous shrubs, and deciduous trees. We found a correlation between diet (described using stable isotope ratios) and accumulation of trace elements in hair using a redundancy analysis, and we detected relationships between diet, trace elements and vital rates using logistic and Cox models. Pregnancy and calf survival probabilities were higher when the δ13C signature of female caribou was higher, and the adult survival probability was higher in caribou that had higher concentrations of zinc and sodium, and lower concentrations of cesium and manganese in their hair. Based on the correlation we found between nutrition and individual performance, our study suggests that nutrition may be an important factor to consider in the recovery of this endangered caribou population.