Dietary and Reproductive Responses of Arctic Foxes to Changes in Small Rodent Abundance

Between 1988 and 1995, dens in three adjacent arctic fox (Alopex lagopus) territories were monitored in an alpine environment in south-central Norway (the Snøhetta plateau). A total of 675 scats were collected at dens in both winter and summer, and the numbers of resident adults and pups at emergence were counted each summer. Small rodents (mainly Lemmus sp. and Microtus sp.) were the most frequently consumed prey and made up the greatest volume within scats, in all seasons and at all stages of the rodent cycle. Small rodents were followed in frequency by reindeer (Rangifer tarandus), hares (Lepus timidus), birds, and vegetation. Birds and vegetation were more common in the summer diet than in the winter diet, reflecting their seasonal availability. The relative volume of reindeer and birds in the diet decreased with increasing rodent abundance. Increased pup production was associated with years of high rodent abundance and a high occurrence of rodents in the diet. Adult numbers were not associated with rodent abundance.Entre 1988 et 1995, on a observé les terriers du renard arctique (Alopex lagopus), dans trois territoires contigus situés dans un environnement alpin du centre-sud de la Norvège (le plateau Snøhetta). En hiver et en été, on a recueilli un total de 675 excréments sur le site des terriers, et chaque été, on a compté le nombre de résidents adultes et de petits qui faisaient leur première sortie du terrier. Les petits rongeurs (surtout Lemmus sp. et Microtus sp.) étaient la proie la plus fréquemment consommée et constituaient le plus gros volume des excréments, en toute saison et à toute étape de la vie du rongeur. Les petits rongeurs étaient suivis en fréquence par le renne (Rangifer tarandus), le lièvre (Lepus timidus), les oiseaux et la végétation. Les oiseaux et les plantes étaient plus courants dans le régime alimentaire estival que dans celui hivernal, ce qui reflétait la disponibilité saisonnière. Le volume relatif de renne et d'oiseaux dans l'alimentation diminuait avec l'augmentation de rongeurs. La production accrue de petits était associée aux années de grande abondance de rongeurs et à une occurrence élevée de rongeurs dans l'alimentation. Le nombre des adultes n'était pas relié à l'abondance de rongeurs

Context-dependent demographic and genetic effects of translocation from a captive breeding project

Translocations are a widespread approach to conserve threatened populations. Given the rapid decline and genetic deterioration of many natural populations, translocations are expected to become even more common in the future. The success of translocations is, however, dependent on multiple context-dependent factors, such as demographic and genetic status, habitat quality and animal behaviour. The Scandinavian arctic fox (Vulpes lagopus) exists in a small, fragmented population that is demographically vulnerable and exposed to inbreeding depression. In the early 2000 s, releases of arctic foxes from the Norwegian Captive Breeding Programme were initiated with the purpose of reintroducing populations to formerly inhabited areas and promoting connectivity. Since 2008/2009, 61 foxes have been released in Junkeren, Norway to re-establish an unoccupied area. We used a combination of field observations and microsatellite genotyping from the release site and two neighbouring subpopulations to investigate (i) the probability of establishment and reproduction for released foxes at the release site and in neighbouring subpopulations, and (ii) the impact on litter size and genetic composition in the recipient populations. Results showed that 18% of the released foxes were established at the release site, or in neighbouring subpopulations and 11.5% reproduced successfully. The extent of post-release dispersal into neighbouring subpopulations was also relatively high (11.5%). During the study period, the number of litters more than doubled in the subpopulations with released foxes contributing 29.5% to this increase, but no clear effect of immigration on litter size was found. There was a slight increase in genetic variation in one of the subpopulations, and a significant decline in genetic divergence between subpopulations. We conclude that despite extensive releases, demographic and genetic effects were highly context-dependent. This study highlights the challenges of reinforcement programmes in small populations and reintroductions to unoccupied sites, especially for highly mobile species in a fragmented landscape. conservation; immigration; translocation; genetic variation; demography; arctic fox; Vulpes lagopus; captive breeding; conservation breeding.publishedVersio

Status and conservation goals for the critically endangered Arctic fox in Scandinavia. Is the mission completed?

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Predator co-occurrence in alpine and Arctic tundra in relation to fluctuating prey

1. Large carnivores influence ecosystem dynamics in multiple ways, for example, by suppressing meso-carnivores and providing carrions for smaller scavengers. Loss of large carnivores is suggested to cause meso-carnivore increase and expansion. Moreover, competition between meso-carnivores may be modified by the presence of larger carnivores. In tundra ecosystems, the smallest meso-carnivore, the Arctic fox, has experienced regional declines, whereas its larger and competitively superior congener, the red fox, has increased, potentially due to changes in the abundance of apex predators. 2. We explored if variation in the occurrence of wolverine and golden eagle impacted the occurrence and co-occurrence of the Arctic fox and red fox in relation to varying abundances of small rodents within the Scandinavian tundra. 3. We applied multi-species occupancy models to an extensive wildlife camera dataset from 2011–2020 covering 98 sites. Daily detection/non-detection of each species per camera trap site and study period (late winter; March–May) was stacked across years, and species occupancy was related to small rodent abundance while accounting for time of the year and status of simulated carcass. 4. The Arctic fox was more likely to co-occur with the red fox when the wolverine was present and less likely to co-occur with the red fox when golden eagles were present and the wolverine was absent. Red foxes increased in occupancy when co-occurring with the larger predators. The Arctic fox responded more strongly to small rodent abundance than the red fox and co-occurred more often with the other species at carcasses when rodent abundance was low. 5. Our findings suggest that the interspecific interactions within this tundra predator guild appear to be surprisingly intricate, driven by facets of fear of predation, interspecific mediation and facilitation, and food resource dynamics. These dynamics of intraguild interactions may dictate where and when conservation actions targeted towards the Arctic fox should be implemented

Fecal glucocorticoid metabolites as an indicator of adrenocortical activity in Arctic foxes (Vulpes lagopus) and recommendations for future studies

Measuring fecal glucocorticoid metabolites (fGCMs) is a widely used, non-invasive method for studies of stress in vertebrates. To study physiological responses in wild Arctic foxes (Vulpes lagopus) to perceived stressors such as fluctuating food availability, occurrence of competitors and predators and disturbance from human activities, a species-specific physiological validation of a method to evaluate adrenocortical activity is needed. Here we used 15 captive Arctic foxes (both males and females and juveniles and adults) to investigate fGCM concentrations following ACTH injection (physiological validation), or handling alone and compared them with their respective baseline concentrations prior to the treatments. A 5α-pregnane-3ß,11ß,21-triol-20-one enzyme immunoassay measured significant fGCM increases following both treatments. The time lags to reach peak fGCM values were 9.3 ± 1.3 h and 12.8 ± 1.7 h for ACTH and handling treatment, respectively. Concentrations of fGCMs varied a lot between individuals, but not attributed to sex nor age of the foxes. However, we found a negative relationship between boldness and fGCM concentrations. Faecal glucocorticoid metabolites concentrations did not change significantly over a period of 48 h in samples kept at temperatures reflecting winter and summer means. This would allow the collection of samples up to two days old in the wild regardless of the season. We conclude that our successfully validated method for measuring fGCMs can be used as a non-invasive tool for studies exploring various stressors both in wild and captive Arctic foxes.publishedVersio

Conservation of the endangered Arctic fox in Norway - are successful reintroductions enough?

Translocation of captive-bred animals has become a widespread conservation practice to counteract species extinctions. We analyse and discuss the apparent success and shortcomings of Arctic fox (Vulpes lagopus) reintroductions in alpine tundra areas of Norway. We followed the fate of 915 foxes between 2007 and 2020 and estimated the apparent survival and reproductive success of captive-bred and released Arctic foxes, compared to wild-born descendants. Relationship to abundance of small rodents, population size, and age were explored. Overall, apparent survival and probability of breeding were similar between captive-bred and wild-born foxes, positively linked to rodent abundance. For wild-born foxes, both breeding propensity and litter size declined with increasing fox population size. This could be a first sign of the limited capacity of single tundra patches to house self-subsistent populations. Thus, facilitating and maintaining connectivity among remnant and re-established Arctic fox populations, creating functional metapopulations, is essential for further improvement and longterm survival. Relying on the combined measures of supplementary feeding and red-fox (Vulpes vulpes) control, the Arctic fox captive-breeding and reintroduction programme has so far been highly successful. However, anthropogenic drivers facilitating red fox invasion into the Arctic fox habitat, along with climate driven irregularities and dampened small rodent cycles, could inhibit the establishment of a self-sustained population. A more holistic ecosystem approach and conservation measures to restore alpine fauna should be considered.publishedVersio

Predation of endangered Arctic foxes by Golden eagles: What do we know?

Dedicated conservation efforts spanning the past two decades have saved the Fennoscandian Arctic fox (Vulpes lagopus) population from local extinction, and ex-tensive resources continue to be invested in the species' conservation and manage-ment. Although increasing, populations remain isolated, small and are not yet viable in the longer term. An understanding of causes of mortality are consequently impor-tant to optimize ongoing conservation actions. Golden eagles (Aquila chrysaetos) are a predator of Arctic foxes, yet little information on this interaction is available in the literature. We document and detail six confirmed cases of Golden eagle depredation of Arctic foxes at the Norwegian captive breeding facility (2019–2022), where foxes are housed in large open-air enclosures in the species' natural habitat. Here, timely detection of missing/dead foxes was challenging, and new insights have been gained following recently improved enclosure monitoring. Golden eagle predation peaked during the winter months, with no cases reported from June to November. This find-ing contrasts with that which is reported from the field, both for Arctic and other fox species, where eagle depredation peaked at dens with young (summer). While the seasonality of depredation may be ecosystem specific, documented cases from the field may be biased by higher survey efforts associated with the monitoring of repro-ductive success during the summer. Both white and blue color morphs were housed at the breeding station, yet only white foxes were preyed upon, and mortality was male biased. Mitigation measures and their effectiveness implemented at the facility are presented. Findings are discussed in the broader Arctic fox population ecology and conservation context. avian predators, carnivores, interspecific competition, intraguild predation, raptors Behavioural ecology, Biodiversity ecology, Conservation ecology, Ecosystem ecology, Evolutionary ecology, ZoologypublishedVersio

Fitness and fur colouration. Testing the camouflage and thermoregulation hypotheses in an Arctic mammal

Selection for crypsis has been recognized as an important ecological driver of animal colouration, whereas the relative importance of thermoregulation is more contentious with mixed empirical support. A potential thermal advantage of darker individuals has been observed in a wide range of animal species. Arctic animals that exhibit colour polymorphisms and undergo seasonal colour moults are interesting study subjects for testing the two alternative hypotheses: demographic performance of different colour morphs might be differentially affected by snow cover with a cryptic advantage for lighter morphs, or conversely by winter temperature with a thermal advantage for darker morphs. In this study, we explored whether camouflage and thermoregulation might explain differences in reproduction and survival between the white and blue colour morphs of the Arctic fox Vulpes lagopus under natural conditions. Juvenile and adult survival, breeding propensity and litter size were measured for 798 captive-bred and released or wild-born Arctic foxes monitored during an 11-year period (2007–2017) in two subpopulations in south-central Norway. We investigated the proportion of the two colour morphs and compared their demographic performance in relation to spatial variation in duration of snow cover, onset of snow season and winter temperatures. After population re-establishment, a higher proportion of blue individuals was observed among wild-born Arctic foxes compared to the proportion of blue foxes released from the captive population. Our field study provides the first evidence for an effect of colour morph on the reproductive performance of Arctic foxes under natural conditions, with a higher breeding propensity of the blue morph compared to the white one. Performance of the two colour morphs was not differentially affected by the climatic variables, except for juvenile survival. Blue morph juveniles showed a tendency for higher survival under colder winter temperatures but lower survival under warmer temperatures compared to white morph juveniles. Overall, our findings do not consistently support predictions of the camouflage or the thermoregulation hypotheses. The higher success of blue foxes suggests an advantage of the dark morph not directly related to disruptive selection by crypsis or thermoregulation. Our results rather point to physiological adaptations and behavioural traits not necessarily connected to thermoregulation, such as stress response, immune function, sexual behaviour and aggressiveness. Our findings highlight the need to explore the potential role of genetic linkage or pleiotropy in influencing the fitness of white and blue Arctic foxes as well as other species with colour polymorphisms

Genomic Consequences of Fragmentation in the Endangered Fennoscandian Arctic Fox (Vulpes lagopus)

Accelerating climate change is causing severe habitat fragmentation in the Arctic, threatening the persistence of many cold-adapted species. The Scandinavian arctic fox (V. lagopus) is highly fragmented, with a once continuous, circumpolar distribution, it struggled to recover from a demographic bottleneck in the late 19th century. The future persistence of the entire Scandinavian population is highly dependent on the northernmost Fennoscandian subpopulations (Scandinavia and the Kola Peninsula), to provide a link to the viable Siberian population. By analyzing 43 arctic fox genomes, we quantified genomic variation and inbreeding in these populations. Signatures of genome erosion increased from Siberia to northern Sweden indicating a stepping-stone model of connectivity. In northern Fennoscandia, runs of homozygosity (ROH) were on average ~1.47-fold longer than ROH found in Siberia, stretching almost entire scaffolds. Moreover, consistent with recent inbreeding, northern Fennoscandia harbored more homozygous deleterious mutations, whereas Siberia had more in heterozygous state. This study underlines the value of documenting genome erosion following population fragmentation to identify areas requiring conservation priority. With the increasing fragmentation and isolation of Arctic habitats due to global warming, understanding the genomic and demographic consequences is vital for maintaining evolutionary potential and preventing local extinctions. inbreeding; runs of homozygosity; bottleneck; fragmentation; mutational load; conservatio

Bycatch in local fishery disrupts natural reestablishment of Eurasian otter in western Norway

Lack of proper estimates of nonreported bycatch has made it difficult to evaluate the actual impact of bycatch in many local fisheries. For the Eurasian otter (Lutra lutra), there are no published estimates on the extent to which bycatch is unreported, despite nonreporting being a well-known issue. Through public outreach efforts in local news and media we collected information from citizen scientists on nonreported otter mortalities of a small-scale fishery in western Norway along the recent natural expansion front of otters. We compared this to deaths that were properly registered by local authorities. In total, cause of mortality was determined from 218 otters between 2003 and 2018. We found that the chances of a mortality being properly reported varied between type of death. Drowning in fyke and gillnets were the most common cause of mortality, and at least 61 and 69% of these deaths were never reported, respectively. The high level of bycatch occurring in the otters' current region of expansion is likely to have demographic impacts and hinder otter reestablishment in the area. Banning the use of fyke nets and setting a minimum fishing depth for gillnets would enhance otter recovery and simultaneously alleviate bycatch of other nontarget species in the region, while having little economic impact on a fishery which is mostly noncommercial. The case of the otter is a classic example of lack of communication between government agencies which have so far failed to establish platforms where issues like this can be discussed and solved by adequate law implementation. bureaucratic barriers, citizen science, drowning, fisheries, law enforcement, Lutra lutra, management failurepublishedVersio