Migratory Caribou Research Articles

Temperature Drives Summer Group Size Dynamics of Eastern Migratory Caribou in the Hudson Bay Lowlands of Manitoba

Aggregation behavior is pervasive across a broad range of animals and the outcome of this behaviour has both risks and rewards. Large aggregations of animals are a distinctive characteristic of Migratory Caribou (Rangifer tarandus Linnaeus, 1758), primarily in response to the environment factors such as predation, although caribou may also aggregate during high summer temperatures, likely in an effort to mitigate parasitic biting flies. To see if caribou in the Cape Churchill Caribou Herd of the Eastern Migratory caribou (Rangifer tarandus groenlandicus Borowski, 1780) Designatible Unit, also displayed aggregation behavior in relation to warmer summer temperatures, we collected trail camera photos with associated temperature readings during the summer period (May to September) from 2017 to 2020 in their summer range in Wapusk National Park, Manitoba, Canada. We found that summer caribou aggregation size was positively associated with ambient temperature, with aggregations increasing in size as temperature increased. The mechanism behind this behaviour should be investigated, as we predict more frequent and large caribou aggregations as summer temperatures continue to warm.

Morphological Traits Are Not Consistently Related to Population Size in Four Migratory Caribou Populations Across North America.

To develop effective management to maintain or restore populations of large herbivores, wildlife managers require sound empirical data on their variations in size and associated parameters. Many studies have highlighted links between morphological traits of individuals and population density; however, less attention has been devoted to whether or not morphological traits can reliably inform on population size in years when no population estimates are available. We evaluated the relationships between three morphological traits (hind foot length, body mass, and body fat) and population size interpolated over three decades, for four migratory caribou (Rangifer tarandus) herds in northern Canada and Alaska. Our sample included 8865 measurements of 4473 individuals. We used a Bayesian modeling approach to evaluate the relationships between morphology and population size across different sex and age classes, considering different temporal scales and, when possible, phases of population growth or decline. We found that morphological traits were not consistently linked to population size. Statistically significant relationships existed for some combinations of herd and age classes, but weak to absent relationships were more common. Our study suggests that morphological traits alone cannot replace data obtained from aerial surveys to approximate population size when population trends are unknown. We discuss the usefulness of morphological traits to explain population size, and recognize their role as complementary metrics to inform the management and conservation of large herbivores, but conclude that morphological data should not be used to predict population size without information on population trends.

Securing the boundaries of wilderness in northern Alaska, 1892–1950

This paper examines the socio-ecological implications of reindeer-caribou hybridization during the rise and collapse of the reindeer industry in Alaska. Following their introduction in the late nineteenth century, reindeer populations increased dramatically as herds spread throughout the territory. As populations increased, domesticated reindeer often escaped from their herds and ran off with migratory caribou. By the 1920s, Alaskan wildlife managers and scientists came to view feral reindeer as a form of biological pollution and a threat to the health and purity of the region's wild caribou. Despite divergent evolutionary histories, reindeer and caribou are related at the subspecies level and can interbreed to produce hybridized offspring. I argue that managerial anxieties about reindeer-caribou hybridization were bound up with broader concerns regarding race and related efforts to protect ostensibly pure spaces of wilderness and nature. Throughout the paper, I consider managerial attempts to mitigate reindeer-caribou hybridization in northern Alaska, which included the demarcation and reinforcement of conceptual and spatial boundaries between wild and domesticated forms of life. However, between the late nineteenth and mid-twentieth centuries, feral reindeer and hybridized caribou repeatedly demonstrated the violability of the biological categories and conceptual boundaries that wildlife managers employed as they sought to order life on the northern tundra.

Simultaneous estimation of the temporal and spatial extent of animal migration using step lengths and turning angles

BackgroundAnimals of many different species, trophic levels, and life history strategies migrate, and the improvement of animal tracking technology allows ecologists to collect increasing amounts of detailed data on these movements. Understanding when animals migrate is important for managing their populations, but is still difficult despite modelling advancements.MethodsWe designed a model that parametrically estimates the timing of migration from animal tracking data. Our model identifies the beginning and end of migratory movements as signaled by change-points in step length and turning angle distributions. To this end, we can also use the model to estimate how an animal’s movement changes when it begins migrating. In addition to a thorough simulation analysis, we tested our model on three datasets: migratory ferruginous hawks (Buteo regalis) in the Great Plains, barren-ground caribou (Rangifer tarandus groenlandicus) in northern Canada, and non-migratory brown bears (Ursus arctos) from the Canadian Arctic.ResultsOur simulation analysis suggests that our model is most useful for datasets where an increase in movement speed or directional autocorrelation is clearly detectable. We estimated the beginning and end of migration in caribou and hawks to the nearest day, while confirming a lack of migratory behaviour in the brown bears. In addition to estimating when caribou and ferruginous hawks migrated, our model also identified differences in how they migrated; ferruginous hawks achieved efficient migrations by drastically increasing their movement rates while caribou migration was achieved through significant increases in directional persistence.ConclusionsOur approach is applicable to many animal movement studies and includes parameters that can facilitate comparison between different species or datasets. We hope that rigorous assessment of migration metrics will aid understanding of both how and why animals move.

Selection of summer feeding sites and food resources by female migratory caribou (Rangifer tarandus) determined using camera collars.

Migratory caribou (Rangifer tarandus) is a socioeconomically and culturally key species for northern communities in the Arctic, and most of its populations are experiencing a sharp decline. Female migratory caribou depend on the availability of summer habitat resources to meet the needs associated with lactation and the accumulation of fat reserves to survive when resources are less abundant. Because of the large scales at which habitat and resource data are usually available, information on how female migratory caribou select habitat and resources at fine scales in the wild is lacking. To document selection of summer feeding sites, we equipped 60 female caribou with camera collars from 2016 to 2018. We collected a total of 65,150 10-sec videos between June 1st and September 1st for three years with contrasted spring phenology. We determined the selection at the feeding site scale (3rd scale of Johnson) and food item scale (4th scale of Johnson) using resource selection probability functions. Wetlands were highly selected as feeding sites in June and July while they were avoided in August. Shrublands were mostly selected in July and August. At the resources scale, lichen, birch, willow, and mushrooms were the most strongly selected resources. Our results provide precise and novel information on habitat selection at feeding sites and food resources selected by female caribou in the wild. This information will help understand foraging patterns and habitat selection behavior of female migratory caribou and will contribute to the management and conservation of its declining populations.

Evidence of migratory coupling between grey wolves and migratory caribou

Large‐scale animal migrations influence population and community dynamics along with ecosystem functioning. The migratory coupling concept posits that movement of migrant prey can lead to large‐scale movements of predators. In northern ecosystems, spatial patterns and behavioral responses of grey wolf to spatio‐temporal changes in its primary prey distribution, the migratory caribou, remain poorly documented. We used a long‐term GPS dataset (2011–2021) of 59 wolves and 431 migratory caribou from the declining Rivière‐aux‐Feuilles herd (QC, Canada) to investigate movement patterns and space use of wolves related to caribou seasonal distribution. Wolves home ranges overlapped with areas used by caribou year‐round, especially in May and winter. Wolves exhibited three annual tactics: sedentary (17%), long‐distance migration (> 700 km) between wintering areas and the tundra (36%), and a medium‐distance migration, stopping their northward movement near the treeline (47%). Migratory wolves started spring migration northward earlier than caribou, intercepting their prey on their way to calving grounds, but departed southward for fall migration later than caribou, tracking them on their way back to wintering areas. Wolves near or overlapping areas used by caribou exhibited lower monthly movement rates compared to wolves located further away. Overlap of home range among wolves was higher during migrations and winter but decreased in summer when wolves rear pups and caribou are dispersed on summer grounds. We provide evidence of migratory coupling between grey wolves and migratory caribou, with most wolves adjusting their space use patterns to match their primary prey distribution. Although predation pressure may affect the dynamics of declining caribou herds, the global decline of that prey may in turn impact predators on the long‐term, potentially enhancing intraspecific competition for new resources. Highlighting this migratory coupling is a key step to develop appropriate conservation and management measures for both guilds in the context of large‐scale migratory prey decline.

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.

Toxoplasma gondii and related Sarcocystidae parasites in harvested caribou from Nunavik, Canada.

Caribou are keystone species important for human harvest and of conservation concern; even so, much is unknown about the impact of parasites on caribou health and ecology. The aim of this study was to determine the seroprevalence, tissue prevalence, and diversity of tissue-dwelling coccidian parasites (including Toxoplasma gondii, Neospora caninum and Sarcocystis spp.) in 88 migratory caribou (Rangifer tarandus) harvested for human consumption in two communities in Nunavik, Québec, Canada. Both T. gondii and N. caninum have potential to cause abortions and neurological disease in caribou. Seroprevalence for antibodies to T. gondii using ELISA on fluid from thawed hearts was 18% overall, and no DNA of T. gondii was detected in tissues, which has positive implications for food safety since this parasite is zoonotic. Seroprevalence for antibodies to N. caninum using competitive ELISA was 5%, and DNA of N. caninum was detected in only one heart sample. DNA of Sarcocystis, a non-zoonotic, related coccidian, was detected in tissue samples from 85% of caribou, with higher prevalence in heart (82%) than skeletal muscle (47%). This is the first time that Sarcocystis spp. from caribou in Canada have been identified to species level, many of which have been described in reindeer from Fennoscandia. The high prevalence and diversity of Sarcocystis spp. suggests intact trophic relationships between canids and caribou in Nunavik. Besnoitia spp. was serendipitously detected in three muscle samples, a parasite previously associated with skin lesions in caribou in Nunavik. Community-level differences in T. gondii exposure and prevalence of Sarcocystis spp. in skeletal muscle tissues may reflect differences in hunter selection of individual animals and muscles, or possibly regional differences in the ecology of carnivore definitive hosts for these parasites. Further work is needed to explore effects of tissue coccidians in caribou, their taxonomic classifications, and community level differences in parasite prevalence and diversity.

Comparison between strip sampling and laser ablation methods to infer seasonal movements from intra-tooth strontium isotopes profiles in migratory caribou

Strontium isotopes analysis is a powerful tool in the study of past animal movements, notably the sequential analysis of tooth enamel to reconstruct individual movements in a time-series. Compared to traditional solution analysis, high resolution sampling using laser-ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) has the potential to reflect fine scale mobility. However, the averaging of the 87Sr/86Sr intake during the enamel mineralization process may limit fine scale inferences. We compared solution and LA-MC-ICP-MS 87Sr/86Sr intra-tooth profiles from the second and third molars of 5 caribou from the Western Arctic herd, Alaska. Profiles from both methods showed similar trends, reflecting the seasonal migratory movements, but LA-MC-ICP-MS profiles showed a less damped 87Sr/86Sr signal than solution profiles. Geographic assignments of the profile endmembers to the known summer and winter ranges were consistent between methods and with the expected timing of enamel formation but showed discrepancy at a finer scale. Variations on LA-MC-ICP-MS profiles, consistent with expected seasonal movements, suggested more than an admixture of the endmember values. However, more work in understanding enamel formation in Rangifer, and other ungulates, and how 87Sr/86Sr daily intake translates into enamel are needed to assess the real resolution that can be achieved with LA-MC-ICP-MS.

Towards long-term records of rain-on-snow events across the Arctic from satellite data

Abstract. Rain-on-snow (ROS) events occur across many regions of the terrestrial Arctic in mid-winter. Snowpack properties are changing, and in extreme cases ice layers form which affect wildlife, vegetation and soils beyond the duration of the event. Specifically, satellite microwave observations have been shown to provide insight into known events. Only Ku-band radar (scatterometer) has been applied so far across the entire Arctic. Data availability at this frequency is limited, however. The utility of other frequencies from passive and active systems needs to be explored to develop a concept for long-term monitoring. The latter are of specific interest as they can be potentially provided at higher spatial resolution. Radar records have been shown to capture the associated snow structure change based on time-series analyses. This approach is also applicable when data gaps exist and has capabilities to evaluate the impact severity of events. Active as well as passive microwave sensors can also detect wet snow at the timing of an ROS event if an acquisition is available. The wet snow retrieval methodology is, however, rather mature compared to the identification of snow structure change since ambiguous scattering behaviour needs consideration. C-band radar is of special interest due to good data availability including a range of nominal spatial resolutions (10 m–12.5 km). Scatterometer and SAR (synthetic aperture radar) data have therefore been investigated. The temperature dependence of C-band backscatter at VV (V – vertical) polarization observable down to −40 ∘C is identified as a major issue for ROS retrieval but can be addressed by a combination with a passive microwave wet snow indicator (demonstrated for Metop ASCAT – Advanced Scatterometer – and SMOS – Soil Moisture and Ocean Salinity). Results were compared to in situ observations (snowpit records, caribou migration data) and Ku-band products. Ice crusts were found in the snowpack after detected events (overall accuracy 82 %). The more crusts (events) there are, the higher the winter season backscatter increase at C-band will be. ROS events captured on the Yamal and Seward peninsulas have had severe impacts on reindeer and caribou, respectively, due to ice crust formation. SAR specifically from Sentinel-1 is promising regarding ice layer identification at better spatial details for all available polarizations. The fusion of multiple types of microwave satellite observations is suggested for the creation of a climate data record, but the consideration of performance differences due to spatial and temporal cover, as well as microwave frequency, is crucial. Retrieval is most robust in the tundra biome, where results are comparable between sensors. Records can be used to identify extremes and to apply the results for impact studies at regional scale.

How Many Generations are Available for Study? Expectations and Applications of Historical Ecological Insight from Bones Lying on Modern Landscapes

Skeletal remains lying on landscape surfaces are useful for evaluating historical states of living populations, but across how much time can such resources inform management and conservation? Further, how do differences in environmental setting impact the breadth of the available timeseries? Using radiocarbon dated bones from across the globe, we evaluated the relationship between the maximum duration that bones persist on landscapes and the mean annual temperature of each locality. We found that bones can persist for several millennia in cold (high-latitude) settings and that there is a strong link (R2 > 0.9, p < 0.01) between local temperature and the logged duration of maximum bone persistence. This relationship provides an initial expectation for the duration across which skeletal remains from different settings can provide historical ecological context. Across the Holarctic, caribou (Rangifer tarandus) are the most abundant large mammal and arguably the most economically significant one for multiple human cultures, including serving as a key nutritional and cultural resource. For migratory caribou, movements between winter ranges and spring calving grounds are among the longest annual migrations of any terrestrial species and maintaining access to these areas is a top conservation priority. But how long have herds used particular calving grounds? Shed female antlers lying on the tundra provide insight into historical calving geography because they are shed within days of giving birth. Following antler surveys across the Coastal Plain calving grounds (Arctic National Wildlife Refuge, Alaska) of the Porcupine Caribou Herd (PCH), we radiocarbon dated three highly weathered female antlers. Antler ages ranged between ~1,600 and >3,000 calendar years ago. These antlers provide the first physical evidence of calving activity on the PCH calving grounds from previous millennia and substantiate the long ecological legacy of the Coastal Plain as a caribou calving ground.

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.

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.

Variation of hair cortisol in two herds of migratory caribou (Rangifer tarandus): implications for health monitoring.

Migratory caribou (Rangifer tarandus sspp.) is an ecotype of conservation concern that is experiencing increased cumulative stressors associated with rapid climate change and development in Arctic Canada. Increasingly, hair cortisol concentrations (HCCs) are being used to monitor seasonal hypothalamic-pituitary-adrenal axis activity of ungulate populations; yet, the effect of key covariates for caribou (sex, season, sampling source, body location) are largely unknown. The objectives of this research were 4-fold: first, we assessed the impact of body location (neck, rump) sampling sites on HCC; second, we assessed key covariates (sex, sampling method, season) impacting HCCs of caribou; third, we investigated inter-population (Dolphin and Union (DU), Bluenose-East (BNE)) and inter-annual differences in HCC and fourth, we examined the association between HCCs and indices of biting insect activity on the summer range (oestrid index, mosquito index). We examined hair from 407 DU and BNE caribou sampled by harvesters or during capture-collaring operations from 2012 to 2020. Linear mixed-effect models were used to assess the effect of body location on HCC and generalized least squares regression (GLS) models were used to examine the impacts of key covariates, year and herd and indices of biting insect harassment. HCC varied significantly by body location, year, herd and source of samples (harvester vs capture). HCC was higher in samples taken from the neck and in the DU herd compared with the BNE, decreased linearly over time and was higher in captured versus hunted animals (P < 0.05). There was no difference in HCC between sexes, and indices of biting insect harassment in the previous year were not significantly associated with HCC. This study identifies essential covariates impacting the HCC of caribou that must be accounted for in sampling, monitoring and data interpretation.

Caribou crossings: the Trans-Alaska Pipeline System, conservation, and stakeholdership in the Anthropocene.

This article engages with notions of conservation in the Anthropocene from a history-of-science perspective. It does so by looking at an iconic case of infrastructure development that since the 1970s continues to cause controversies amongst wildlife experts: the Trans-Alaska Pipeline System (TAPS). I examine how, from the 1970s onwards, the TAPS functioned as an experimental device for ecologists to test the adaptability of migratory caribou to changed environments and their dependency on unaltered ranges. Based on archival research, published reports and interviews, I show that arguments about animal learning, despite assigning a more active role to caribou in the conservation process, did not result in more inclusive forms of development that respected ecological processes and the various stakes of the caribou. In fact, a focus on caribou crossings as an easily observable, yet sole, indicator of the pipeline's impact resulted in a simplified representation of environmental relationships, that was used by the oil industry to argue for additional extraction projects. Arguments based on the material interdependencies of caribou with their environment, though seemingly similar to traditional arguments about range preservation, emerged as part of conservationists' attempts to account for the ecological stakes of caribou, other animals and people.

Mechanistic movement models identify continuously updated autumn migration cues in Arctic caribou

BackgroundMigrations in temperate systems typically have two migratory phases, spring and autumn, and many migratory ungulates track the pulse of spring vegetation growth during a synchronized spring migration. In contrast, autumn migrations are generally less synchronous and the cues driving them remain understudied. Our goal was to identify the cues that migrants use in deciding when to initiate migration and how this is updated while en route.MethodsWe analyzed autumn migrations of Arctic barren-ground caribou (Rangifer tarandus) as a series of persistent and directional movements and assessed the influence of a suite of environmental factors. We fitted a dynamic-parameter movement model at the individual-level and estimated annual population-level parameters for weather covariates on 389 individual-seasons across 9 years.ResultsOur results revealed strong, consistent effects of decreasing temperature and increasing snow depth on migratory movements, indicating that caribou continuously update their migratory decision based on dynamic environmental conditions. This suggests that individuals pace migration along gradients of these environmental variables. Whereas temperature and snow appeared to be the most consistent cues for migration, we also found interannual variability in the effect of wind, NDVI, and barometric pressure. The dispersed distribution of individuals in autumn resulted in diverse environmental conditions experienced by individual caribou and thus pronounced variability in migratory patterns.ConclusionsBy analyzing autumn migration as a continuous process across the entire migration period, we found that caribou migration was largely related to temperature and snow conditions experienced throughout the journey. This mechanism of pacing autumn migration based on indicators of the approaching winter is analogous to the more widely researched mechanism of spring migration, when many migrants pace migration with a resource wave. Such a similarity in mechanisms highlights the different environmental stimuli to which migrants have adapted their movements throughout their annual cycle. These insights have implications for how long-distance migratory patterns may change as the Arctic climate continues to warm.

Landscape features and caribou harvesting during three decades in Newfoundland

ABSTRACT Landscapes can influence the distribution of harvesting by influencing animal distribution and hunter access. For species like caribou, Rangifer tarandus, decades-long shifts in abundance and distribution might alter such relationships, but few studies have been conducted at such scales. We examined relationships between landscape features and 21,380 harvest records of migratory caribou in Newfoundland during caribou population growth (1980s), cessation of growth (1990s), and decline (2000s). We focused on features hypothesized to influence the distributions of caribou and hunters: lichen landcover, roads, cutblocks, outfitter camps, power lines, and towns. We uncovered larger harvests by resident hunters of male and female caribou among lichen landcover, likely providing preferred caribou forage, and larger harvests by non-resident hunters of male caribou away from towns, reflecting the locations of outfitter camps. Only during later decades, resident harvests occurred nearer power lines and cutblocks, likely providing hunter access and reflecting risk-prone foraging by caribou. We surmise that the harvest was facilitated by open habitats, preferred by caribou, and anthropogenic features leading to hunter access, especially as the caribou population declined. Such knowledge at broad scales is increasingly important in an era of widespread disruption to landscapes.

Determinants of migration trajectory and movement rate in a long-distance terrestrial mammal

Abstract Animal migrations occur in many taxa and are considered an adaptive response to spatial or temporal variations in resources. Human activities can influence the cost-benefit trade-offs of animal migrations, but evaluating the determinants of migration trajectory and movement rate in declining populations facing relatively low levels of human disturbance can provide new and valuable insights on the behavior of wildlife in natural environments. Here, we used an adapted version of path selection functions and quantified the effects of habitat type, topography, and weather, on 313 spring migrations by migratory caribou (Rangifer tarandus) in northern Québec, Canada, from 2011 to 2018. Our results showed that during spring migration, caribou selected tundra and avoided water bodies, forest, and higher elevation. Higher precipitation and deeper snow were linked to lower movement rates. Weather variables had a stronger effect on the migration trajectories and movement rates of females than males. Duration of caribou spring migration (mean of 48 days) and length (mean of 587 km) were similar in males and females, but females started (22 April) and ended (10 June) spring migrations ca. 6 days earlier than males. Caribou spring migration was influenced by habitat type, topography, and weather, but we also observed that caribou migrations were not spatially constrained. Better knowledge on where and when animals move between their winter and summer ranges can help inform management and land planning decisions. Our results could be used to model future migration trajectories and speed of caribou under different climate change scenarios.

Using Camera Collars to Study Survival of Migratory Caribou Calves

ABSTRACTMonitoring survival of juveniles in wild populations of vertebrates is challenging because capture and marking of neonates may influence survival and induce biases. Camera collars have proven effective in resource and habitat selection studies, but their effectiveness to assess offspring survival is unknown. Our objective was to monitor the survival of neonates using camera collars installed on 24 preparturient female migratory caribou (Rangifer tarandus) of the Rivière‐aux‐Feuilles herd, from 2016 to 2018, in Nunavik, Canada. Females were captured with a net gun fired from a helicopter and pregnancy was confirmed by ultrasound. Cameras recorded a 10‐second video every 20 min from 1 June until 1 September 2017, when the collar detached automatically. We used Cormack‐Jolly‐Seber models to assess survival and resighting probabilities of calves based on their observation in the videos. Three collars failed, recording less than 30% of the expected videos, including one on a female that did not give birth. Among the 21 females wearing a functional collar, one gave birth to a stillborn calf. We analyzed 25,820 videos recorded from 20 collars. Calf sightings in videos were less frequent as the monitoring period advanced, but we estimated the probability of observing a live calf at 0.77 (SE = 0.42) over the sampling period. Videos indicated a survival rate of 0.67 (SE = 0.11) from birth to 1 September. Our results suggest that camera collars installed on adult females can be used to reliably assess offspring survival, and thus improve our understanding of caribou population dynamics. The application of camera collars should be useful for other large vertebrate species for which the assessment of neonate survival is lacking or difficult to obtain. © 2021 The Wildlife Society.

How will snow retention and shading from Arctic shrub expansion affect caribou food resources?

ABSTRACT Increased snow cover and attenuation of light due to shrub expansion can lead to changes in the quantity and nutritional quality of food resources for migratory caribou (Rangifer tarandus). To determine how vegetation is affected by snow accumulation and shade, we conducted an experiment that simulated the light and snow conditions created by increased shrub cover at Deception Bay (Nunavik, Canada), within the summer range of the Rivière-aux-Feuilles caribou herd. We estimated the foliar biomass of two major components of the caribou diet (Betula glandulosa and Carex spp.). We also harvested foliar tissue to conduct chemical composition analyses (nitrogen, fibre, total phenolics). Experimental light attenuation was found to increase the nitrogen concentrations in B. glandulosa and Carex spp. throughout the growing season. Phenolic concentration in B. glandulosa decreased in early summer but was otherwise consistent in response to light attenuation and increased snow cover. Increased snow cover combined with ambient light had a positive effect on the foliar biomass of B. glandulosa. Increased snow cover and shade caused by shrub densification may therefore increase forage quantity and quality for caribou. We suggest investigating the effects of shrub expansion on other components of the caribou diet, such as lichens and forbs.