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Colonial seabirds have adopted certain strategies to minimize breeding losses during fledging. This review focuses on the most numerous high-Arctic auks: Little Auk Alle alle and Brünnich's Guillemot Uria lomvia. Colonies of Little Auks are usually situated farther from the sea than cliff-nesting guillemots. On departing the nest, Little Auk chicks are more advanced and can fly, while guillemot chicks, lacking flight feathers, jump from the cliff ledges and glide to the sea. Little Auk chicks lose weight before departure, thus improving their flight efficiency. In both species, fledglings have strong legs and a thick layer of feathers on the underside to prevent injury from hard landings. Some chicks reach the sea on foot. The fathers care for their fledglings, with whom they are in vocal contact. On land, chicks are hunted by Arctic foxes Vulpes lagopus and gulls Larus sp. When attacked by gulls at sea, young auks dive. In the air, however, only young Little Auks perform a characteristic nose-diving manoeuvre to confuse the predator. Guillemot parents can effectively counteract gull attacks on their young, while Little Auk parents do not directly defend their chicks. Unlike Little Auks, several adult guillemots usually accompany chicks during gliding and landing at sea. Adult guillemots gather near the colony during the fledging period and call loudly, thus indicating a safe landing place. In both species, fledging is highly synchronized and condensed into a few days and night-time hours, thus causing a swamping effect that reduces total losses among fledglings. [ABSTRACT FROM AUTHOR]

Climate warming is favoring the expansion of non-native species onto the Arctic tundra, where they may compete over resources with native species. In the harsh tundra conditions, sympatric red foxes (Vulpes vulpes) and Arctic foxes (Vulpes lagopus) may compete over denning sites, which are important for their reproduction and survival. We studied den selection by red and Arctic foxes in spring and summer and their possible competition over this resource in an ecotone near Churchill, Manitoba, on the west coast of Hudson Bay, by examining patterns of den occupancy related to den characteristics and spacing patterns between neighbors. Based on 11 years of occupancy data for 42 tundra dens, we determined that red and Arctic foxes favored dens based on shelter quality in both spring and summer, rather than proximity of specific habitats (and thus specific prey). Mechanisms of den selection differed between species, which may promote coexistence, and areas of high den density were avoided by red foxes and preferred by Arctic foxes. We did not find evidence of exclusion of Arctic foxes by red foxes: spacing patterns showed that foxes spaced themselves based on their need for space, territoriality and food availability but not interference. In the current abiotic Arctic conditions, taiga species settling on the tundra could coexist with tundra endemics, at given density thresholds of both competitors. As Arctic conditions may become milder, an increase in newcomer abundance could disrupt the current balance that favors species coexistence. [ABSTRACT FROM AUTHOR]

Anthropogenic debris, including plastic pollution, is a growing concern in the Arctic and negatively impacts both marine and coastal organisms. The aim of this study was to investigate the potential for using Arctic fox (Vulpes lagopus) faeces as a monitoring tool for plastic pollution in the Arctic environment. Arctic fox faeces were collected in different regions of Iceland and analysed for anthropogenic debris presence larger than 300 µm, and diet composition. In total, 235 faecal samples from 1999, 2017, 2018 and 2020 were analysed. The overall frequency of occurrence of plastic and other anthropogenic material was 5.11% and was found in samples across all regions and years. There were no statistical differences in anthropogenic debris ingested, depending on year or region. There were no obvious differences in diet composition between samples that contained anthropogenic debris and samples without. The suitability of Arctic fox faeces as a method to monitor plastic and anthropogenic debris levels in the Arctic environment remains debatable: Whilst the vast distribution range of the Arctic fox and the non-invasive collection methodology of faecal samples could be utilised as a good monitoring tool, the overall low uptake and unclear source of plastic and anthropogenic debris (marine or terrestrial) makes the interpretation of the data difficult. Nevertheless, debris ingestion by Arctic foxes remains a concern and warrants further studies. [ABSTRACT FROM AUTHOR]

For the conservation and management of the Arctic regions vulnerable to climate change, it is important to elucidate the trophic relations and food sources for consumers in the ecosystems. We analyzed DNA extracted from feces to understand the summer diets of the major terrestrial animals and their trophic relations in tundra ecosystems near Kongsfjorden, Svalbard. Feces of Svalbard reindeer (Rangifer tarandus platyrhynchus), Barnacle Goose (Branta leucopsis), Arctic fox (Vulpes lagopus), and Rock Ptarmigan (Lagopus muta) were collected during the summer seasons of 2014, 2015, 2018, and 2019. Plant DNA was detected in the feces of herbivores (reindeer, goose, and ptarmigan) and vertebrate DNA was detected in the feces of carnivore (Arctic fox) by amplifying, cloning, and Sanger sequencing. In case of Arctic fox, VulpesB, the blocking primer preventing from amplifying Arctic fox DNA, was used to improve the detection of their prey DNA. Salix was the most detected genus in feces of Svalbard reindeer and Barnacle Goose, which were described as feeding on graminoids, forbs, and prostrate as well as bryophyte. Bryophyte was added as an important food source for all herbivores. Arctic fox preferred birds such as geese (Anatidae) and gulls (Laridae), showing that interpretation between Arctic foxes and gulls may have occurred at the same predator level. Our results suggest that cloning-based DNA analysis using fecal sample contributes to understanding the tundra terrestrial food web near Kongsfjorden. [ABSTRACT FROM AUTHOR]

Selecting the right location for a den during the breeding season is a type of habitat selection in the Arctic fox (Vulpes lagopus) that is likely to affect its reproductive success. A den's suitability likely depends on its ability to provide shelter, as well as its proximity to prey resources. Depending on the different relative risks that Arctic foxes may face across their broad circumpolar range, Arctic foxes may place different emphases on selection for shelter and prey resources in different ecosystems. Understanding the different requirements for reproduction under different ecological conditions is highly relevant to conservation efforts in areas where Arctic foxes are threatened by rapid environmental changes. Here, we investigated the relative selection for shelter and prey resources in southern Yamal Peninsula (Russia) using data from 45 dens collected over a 13-year period. Arctic foxes preferred to breed in dens with more den entrances; an indicator of shelter quality. Arctic foxes also preferred dens surrounded by more prey resources (quantified by the amount of river valley habitat), but this result was less conclusive. These results complement the findings reported from other study areas, illustrating that Arctic foxes in ecosystems with diverse predator communities may put emphasis on selection for shelter quality. In less productive ecosystems, Arctic foxes may rather put emphasis on selection for prey resources. As tundra ecosystems become more productive and generalist predators move north, the reproductive requirements and habitat selection of Arctic foxes may change accordingly, depending on the species' ability to adapt. [ABSTRACT FROM AUTHOR]

Despite the availability of ever more data on population trends in Arctic waders, we still have limited insight into the factors influencing reproductive success and its resulting contribution to population trajectories. Here, we present data from Zackenberg in high Arctic Greenland that show no changes in timing of egg laying nor clutch size over more than two decades. With variation among species, we found earlier egg laying in seasons with earlier snowmelt, more invertebrates during the pre-laying period, earlier appearance of invertebrates and higher June temperatures. In addition, we found larger clutch sizes with earlier snowmelt, and lower clutch sizes with later nest initiation dates, together with increasing variability in clutch size during the study years in one species. Nest success was lower in late breeding seasons but seemed to increase with season progress, while nest success was much lower during the lasts 18 years of the study period than during the first part of the period. The reason for this could be both increased Arctic fox activity on the tundra and increased researcher activity at nests, which leaves olfactory clues for the foxes. Numbers of juvenile Dunlins produced seem to be negatively correlated with our index of fox activity on the tundra during nesting and fledging, whereas we found no correlations between fox activity and lemming abundance. The effects of severe events in a number of years are described, including a next to non-breeding year in 2018. Our study adds to our understanding that the Arctic is not a homogeneous biome but may show quite different regional patterns of climate change effects. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Arctic fox (Vulpes lagopus), occupying tundra habitats with highly variable resource distribution, is a convenient research model for studying the impact of food availability on space use. Previous studies have shown that the Arctic fox home ranges can vary from 4 to 125 km2. In areas with abundant food resources, home range sizes are smaller and overlap increases. It is theoretically assumed that with an excess of resources, territoriality should disappear. We investigated a fox settlement at the Northern fur seal rookery on Bering Island (North Pacific). We used GPS collars to track nine foxes in the summer of 2014 and 2016. GPS locations were recorded at 5-min intervals. In the home range estimation, we used the Brownian bridge movement model. We also calculated home range sizes using 100% minimum convex polygon (MCP100) and 95% fixed kernel methods to compare our results with previous studies. Home ranges were extremely small with an average of 0.5 km2 (range of 0.2–0.9 km2) by Brownian Bridge and 0.7 km2 (0.3–1.4 km2) by MCP100. We revealed no sex differences in home range size but discovered strong differentiation of activity spatial concentration between males and females. We found a surprisingly small overlap between neighboring foxes, reflecting high territoriality. This runs counter to the trend expected with an overabundant food source. We assume that the combination of the super small size of the home ranges and their exclusivity may be a feature of the island fox land tenure system, which prevents inbreeding and deters infanticide. [ABSTRACT FROM AUTHOR]

The Arctic fox (Vulpes lagopus L.) population on the Kola Peninsula occupies an intermediate, and potentially connecting, position between foxes living on the Scandinavian Peninsula and populations further east in Russia, but very little is known about the status of this population. Here we summarize data from the literature, forgotten archival sources about research in the first half of the twentieth century, and the results of several independent expeditions undertaken over the past two decades. These materials include data on fur harvesting, incomplete monitoring data from official winter track counts of game animals, local knowledge, and our own observations. Our research revealed the extremely poor state of the Arctic fox population on the Kola Peninsula. According to our estimates, the current population is likely isolated and consists of no more than a few dozen adults. The fur return data, together with long-term data on small rodent abundance, suggest that irregular and fading out lemming cycles were a major driver of the Arctic fox population decline. The thorough research from the 1930s contrasts strongly with the lack of interest in studying and monitoring the population in recent decades, which is not even listed as a threatened species in the regional Red Data Book. In fact, the work performed here filled a more than a half-century gap in the study of the population and allowed us to determine the urgent need to resume research and immediately take active measures to protect and promote the recovery of the species in the region. [ABSTRACT FROM AUTHOR]

Studies of the effects of variation in resource availability are important for understanding the ecology of high-latitude mammals. This paper examines the potential of dental evidence (tooth wear and breakage) as a proxy for diet and food choice in Vulpes lagopus, the Arctic fox. It presents a preliminary study of dental microwear, gross wear score, and tooth breakage in a sample (n = 78 individuals) from the Yamal Peninsula of the Russian Arctic. While these measures have each been associated with feeding ecology in larger carnivorans (e.g., proportion of bone in the diet), they have yet to be combined in any study and have rarely been applied to smaller species or those from high latitudes. Arctic foxes from the north and south of the peninsula, and those from rodent peak and trough density periods, are compared to assess impact of changes in food availability across space and time. Results indicate that microwear textures vary in dispersion, with more variation in texture complexity, including higher values (suggesting more consumption of bone), in the rodent-poor period in the north of Yamal. Gross wear scores and tooth breakage are also significantly higher for the north of Yamal than the south. These data together suggest that dental evidence can provide important insights into variation in the feeding ecology of Arctic foxes and potentially into the impacts of changes in food abundance across space and time. [ABSTRACT FROM AUTHOR]

Food hoarding is often considered an adaptive behaviour to extend the period of availability of food resources. Finding the right caching site for storage and retrieval is of paramount importance, yet how caching sites are selected is poorly known. Here, we examine site selection for egg caching by a tundra predator, the arctic fox, Vulpes lagopus, which can overcome large seasonal prey variations by extensive caching. During the short arctic summer, colonial breeding birds like geese produce in a short time period many eggs, which provide a large quantity of predictable resources for consumption and caching. We predicted that foxes would select caching sites with specific characteristics, such as shallow permafrost, and tall hummocks (small mounds in tundra landscapes, which should facilitate caching and provide visual cues for subsequent retrieval). We sampled the main physical characteristics of 48 caches and paired random sites inside a Greater Snow Goose (Chen caerulescens) colony. Our study shows that foxes favour cache sites characterized by hummocks nearly twice as higher than at nearby random sites. The depth of the active layer of permafrost did not influence cache site selection. Foxes may select tundra features that possibly enhance caching efficiency and retrieval probability. Our study elucidates one aspect of food hoarding behaviour in extreme habitats characterized by strong variations of resource availability. [ABSTRACT FROM AUTHOR]

Mating patterns are highly context-dependent and the outcome of selection pressures formed by ecological factors, inbreeding levels and access to available partners. In small and inbred populations, matings are limited by high kin encounter rates and access to mates. In this paper, we use background pedigree data to investigate mating patterns and inbreeding avoidance in an isolated and critically endangered Arctic fox (Vulpes lagopus) population. Empirical data showed avoidance of matings within natal family. Based on 35 documented matings, we only recorded two full-sibling matings and these occurred between individuals from different natal families. Matings between second-order relatives, however, occurred to the same extent as between unrelated individuals. To test how this influenced the population development of inbreeding (f), we simulated scenarios of random mating, exclusion of natal family and exclusion of individuals in already existing pair bonds. The observed development of inbreeding did not correspond the expected scenario of random mating (linear regression, r2 = 0.354, P = 0.20), but showed a comparable outcome as the simulated development of discriminating natal family (linear regression, r2 = 0.980, P < 0.001). We conclude that behavioural, pre-copulatory inbreeding avoidance strategies occur in this population and that exclusion of mating with natal family causes a slower increase in inbreeding levels compared to random mating. This study demonstrates how long-term monitoring, pedigree construction and simulations can generate information valuable for an in-depth understanding of both conservation genetics and behavioural ecology in threatened populations. [ABSTRACT FROM AUTHOR]

Breeding geese are the preferred prey of the Arctic fox Vulpes lagopus in the high-Arctic Svalbard archipelago. According to the apparent competition hypothesis (ACH), less-abundant prey species (e.g. ptarmigan, waders and small passerines) will experience higher predation rates when breeding in association with the more common prey (geese), due to spill-over predation by the shared predator. As many of these less-abundant species are endemic and/or red-listed, increased predation can have negative repercussions on their populations. We used a one-year baited artificial nest study to assess relative nest predation risk on Svalbard Rock Ptarmigan Lagopus muta hyperborea, small waders (Purple Sandpiper Calidris maritima, Dunlin Calidris alpina, plovers Charadrius spp., and phalaropes Phalaropus spp.) and Snow bunting Plectrophenax nivalis in two study locations contrasted by nesting density of Arctic breeding geese (Pink-footed Goose Anser brachyrhynchus and Barnacle Goose Branta leucopsis). We predicted higher predation risk for the less-abundant species in the study location with higher goose abundance. However, we found that relative nest predation risk was lower in the study location with higher goose abundance, thus being compatible with apparent mutualism and/or prey swamping mechanisms. Our results contrast with those from more structurally complex Arctic ecosystems and suggest that allochtonous subsidies from temperate ecosystems structure the predation pattern in this high-Arctic tundra ecosystem. [ABSTRACT FROM AUTHOR]

Global climate change induces species range shifts and population expansion to higher latitudes in response to rising temperatures. One consequence of climate-induced range shifts is an increased sympatry between related but previously isolated species, potentially resulting in interspecific interactions and hybridization. The Arctic is more rapidly affected by climate warming than any region on Earth and resident species may be prone to interspecific hybridization due to the immigration of new colonizing species. The red fox Vulpes vulpes expanded its range into the Arctic during the twentieth century and is now in sympatry with the native Arctic fox Vulpes lagopus in many places. In this context, an Arctic-like fox displaying an unusual reddish winter coat was observed in 2013 in Nunavut, Canada, a phenotype unknown by Inuit people to date. In this study, we assessed the biological origin of this specimen with a multigenic approach using markers located on mitochondrial DNA, sex (X and Y) chromosomes, and autosomes (microsatellites and the melanocortin 1 receptor (MC1R) gene; a gene involved in the color polymorphism in canids). Our comparative analyses with genetic material from Arctic and red foxes displaying 'classic' phenotypes ( N = 14 and 16, respectively) suggested a pure Arctic fox origin of the specimen. Specifically, this fox yielded mtDNA, X-linked, Y-linked, and MC1R alleles specific to Arctic fox. Bayesian genetic assignment based on 16 microsatellite loci assigned it to Arctic fox with high confidence ( q = 99.7%). Thus, a recent hybrid origin for this specimen is excluded. This alternative winter coat color polymorphism in Arctic fox requires further analyses to determine its underlying genetic mechanism. [ABSTRACT FROM AUTHOR]

The article offers information on the Canine distemper virus (CDV) as the cause of most of the epizootics. Topics discussed include information on the understanding how the disease spreads in the Arctic environment and ecosystem; discussions on the role of the historical records in providing valuable input for understanding the Arctic epizootic; and the information on the health-related challenges that the Greenland sled dogs face.

Identifying correctly trophic interactions is important for understanding population dynamics and ecosystem functioning. However, some predator-prey relationships may still remain undetected, due to the difficulty of observing rare predation events. We report the first observation of predation of arctic fox ( Vulpes lagopus) pups by common ravens ( Corvus corax). The predation event was witnessed on Bylot Island, Nunavut, Canada, through an automatic camera placed on a den. On June 8, 2013, the day following pup emergence from the den, the complete litter of four was killed and taken away by a pair of ravens despite the intermittent presence of the mother. This event lasted 2.5 h, occurred during a low lemming year, and resulted in the fox pair failing their reproduction. Only two other fox litters were present that summer in our 600 km study area, so this litter predated by ravens accounted for 25 % (4/16) of the pups produced. Our report shows how continuous monitoring of dens using automatic cameras can allow documentation of rare events. In addition to food competition and cache raiding, pup predation contributes to the antagonistic interactions between arctic foxes and ravens in the High Arctic, which may intensify during low lemming years. This observation allows a better understanding of species interactions within the Arctic predator guild. [ABSTRACT FROM AUTHOR]

After infection with Trichinella spp. was first demonstrated in the arctic fox population in Svalbard 30 years ago, there have been changes in the Svalbard ecosystem related to abundance of polar bear and walrus, both reservoir species for Trichinella. In order to update the assessment of the infection rate and search for differences between sex, age, trapping season and location of trapping sites, we examined arctic foxes from Svalbard in 1996-2004 ( n = 429) for antibodies against Trichinella spp. For support and muscle larvae (ML) identification, the diaphragm of a subsample of 330 of the foxes, 40 foxes from 2007 to 2008, and a polar bear ( Ursus maritimus) tongue sample, were examined for ML by an HCl-pepsin digestion method. The antibody assay (enzyme-linked immunosorbent assay, ELISA) demonstrated a seroprevalence of 11.7 %. The prevalence increased with age, was similar in females and males, and body condition was similar in seropositives and seronegatives. There were differences in prevalence between trapping seasons and sites. A previously reported spatial (north-south) difference appeared to be eliminated. The seroprevalence was significantly higher in males (50.0 %) than females (20.0 %) of age 4 years and older. An ML prevalence of 6.7 % was demonstrated for the foxes. This was probably an underestimate due to small sample weights. ML were found also in the polar bear. Multiplex PCR identified eleven ML isolates, ten from the arctic foxes and the polar bear isolate, as Trichinella nativa. [ABSTRACT FROM AUTHOR]

The red fox ( Vulpes vulpes) expanded its distribution over large parts of the Canadian Arctic during the twentieth century and is now considered a threat to the arctic fox ( Vulpes lagopus). Some authors have proposed that the European red fox, introduced in Eastern North America during the eighteenth century, may have spread and caused the species' expansion in the Arctic. Assessing the biological origin of red foxes in the Nearctic is critical to determine whether their presence constitutes a case of an invading exotic species. We analyzed genetic material obtained from four red foxes at Herschel Island (Yukon) and Bylot Island (Nunavut), at the northern expanding front of the species. Samples from Bylot provide the northernmost genetic information on red fox obtained worldwide. We identified mitochondrial DNA haplotypes in red foxes from both Arctic locations that were phylogenetically divergent from those in Eurasia, but shared with neighboring indigenous North American populations. Thus, our results indicate that the twentieth century expansion of red foxes in the Canadian Arctic involved nearby populations potentially benefiting from habitat changes, rather than an exotic species invading new habitats. [ABSTRACT FROM AUTHOR]

Pink-footed geese Anser brachyrhynchus nest in two contrasting but commonly found habitats: steep cliffs and open tundra slopes. In Svalbard, we compared nest densities and nesting success in these two environments over ten breeding seasons to assess the impact of spring snow cover, food availability to nesting adults and arctic fox Vulpes lagopus (main terrestrial predator) abundance. In years with extensive spring snow cover, fewer geese at both colonies attempted to breed, possibly because snow cover limited pre-nesting feeding opportunities, leaving adults in poor breeding condition. Nesting success at the steep cliff colony was lower with extensive spring snow cover; such conditions force birds to commit to repeated and prolonged recess periods at far distant feeding areas, leaving nests open to predation. By contrast, nesting success at the open tundra slope was not affected by spring snow cover; even if birds were apparently in poor condition they could feed immediately adjacent to their nests and defend them from predators. Foxes were the main nest predator in the open tundra slopes but avian predators likely had a larger impact at the steep cliffs colony. Thus, the relative inaccessibility of the cliffs habitat may bring protection from foxes but also deprives geese from readily accessing feeding areas, with the best prospects for successful nesting in low spring snow cover years. Our findings indicate that spring snow cover, predator abundance and food proximity did not uniformly influence nesting success of this herbivore, and their effects were dependent on nesting habitat choice. [ABSTRACT FROM AUTHOR]

With increased polar anthropogenic activity, such as from the oil and gas industry, there are growing concerns about how Arctic species will be affected. Knowledge of species' sensory abilities, such as auditory sensitivities, can be used to mitigate the effects of such activities. Herein, behavioral audiograms of two captive adult Arctic foxes ( Vulpes lagopus) were measured using a yes/no paradigm and descending staircase method of signal presentation. Both foxes displayed a typical mammalian U-shaped audiometric curve, with a functional hearing range of 125 Hz-16 kHz (sensitivity ≤ 60 dB re: 20 μPa) and average peak sensitivity of 24 dB re: 20 μPa at 4 kHz. The foxes had a lower frequency range and sensitivity than would be expected when compared to previous audiograms of domestic dogs ( Canis familiaris) and other carnivores. These differences indicate Arctic foxes ( V. lagopus) may have a lower frequency range than previously expected, which was similar to the only other fox species tested to date, kit foxes (Vulpes macrotis). Alternatively, differences may be due to testing constraints, such as masking of test signals by ambient noise and/or an unintentionally trained conservative response bias, which most likely resulted in underestimated hearing curves. While results of this study should be interpreted with caution due to its limitations, findings indicate that foxes have a narrower frequency range than formerly presumed. Anthropogenic activities near fox habitats can mitigate their impacts by reducing noise at frequencies within the functional hearing range and peak sensitivities of this species. [ABSTRACT FROM AUTHOR]

In the twentieth century, red fox ( Vulpes vulpes) expanded into the Canadian Arctic, where it competes with arctic fox ( Vulpes lagopus) for food and shelter. Red fox dominates in physical interactions with the smaller arctic fox, but little is known about competition between them on the tundra. On Hershel Island, north Yukon, where these foxes are sympatric, we focused on natal den choice, a critical aspect of habitat selection. We tested the hypothesis that red fox displaces arctic fox from dens in prey-rich habitats. We applied an approach based on model comparisons to analyse a 10-year data set and identify factors important to den selection. Red fox selected dens in habitats that were more prey-rich in spring. When red foxes reproduced, arctic fox selected dens with good springtime access, notably many burrows unblocked by ice and snow. These provided the best refuge early in the reproductive season. In the absence of red foxes, arctic foxes selected dens offering good shelter (i.e. large isolated dens). Proximity to prey-rich habitats was consistently less important than the physical aspects of dens for arctic fox. Our study shows for the first time that red foxes in the tundra select dens associated primarily with prey-rich areas, while sympatric arctic foxes do not. These results fit a model of red fox competitively interfering with arctic fox, the first detailed study of such competition in a true arctic setting. [ABSTRACT FROM AUTHOR]

Food availability can impact group formation in Carnivora. Specifically, it has been suggested that temporal variation in food availability may allow a breeding pair to tolerate additional adults in their territory at times when food abundance is high. We investigate group occurrence and intraspecific tolerance during breeding in a socially flexible canid, the arctic fox ( Vulpes lagopus). We compare Iceland and Sweden where resource conditions differ considerably. A breeding pair was the most common social unit in both populations, but as predicted, groups were more frequent where food abundance varied substantially between years (Sweden: 6 %) than where food availability was stable (Iceland: ≤2 %). Within Sweden, supplemental feeding increased group occurrence from 6 to 21 %, but there was no effect of natural variation in lemming ( Lemmus lemmus) availability since group formation was rare also at lemming highs. Thus, additional factors appeared to influence the trade-off between intraspecific territoriality and tolerance. We report two cases where related females showed enduring social relationships with good-neighbour strategies. Related females also engaged in alloparental behaviour in a 'fox town' with 31 foxes (4 adults, 3 litters). In contrast, when unrelated foxes bred close to each other, they moved or split their litters during summer, presumably because of territorial conflict. We suggest that fluctuating food availability is linked to group formation in this Arctic carnivore, but also when food availability increases, additional factors such as relatedness, alloparental benefits, competition and predator defence appear necessary to explain group formation. [ABSTRACT FROM AUTHOR]

During the last century, the red fox ( Vulpes vulpes) has expanded its distribution into the Arctic, where it competes with the arctic fox ( Vulpes lagopus), an ecologically similar tundra predator. The red fox expansion correlates with climate warming, and the ultimate determinant of the outcome of the competition between the two species is hypothesized to be climate. We conducted aerial and ground fox den surveys in the northern Yukon (Herschel Island and the coastal mainland) to investigate the relative abundance of red and arctic foxes over the last four decades. This region has undergone the most intense warming observed in North America, and we hypothesized that this climate change led to increasing dominance of red fox over arctic fox. Results of recent surveys fall within the range of previous ones, indicating little change in the relative abundance of the two species. North Yukon fox dens are mostly occupied by arctic fox, with active red fox dens occurring sympatrically. While vegetation changes have been reported, there is no indication that secondary productivity and food abundance for foxes have increased. Our study shows that in the western Arctic of North America, where climate warming was intense, the competitive balance between red and arctic foxes changed little in 40 years. Our results challenge the hypotheses linking climate to red fox expansion, and we discuss how climate warming's negative effects on predators may be overriding positive effects of milder temperatures and longer growing seasons. [ABSTRACT FROM AUTHOR]

Here, we report from the first direct observation of a red fox ( Vulpes vulpes) intrusion on an arctic fox ( Vulpes lagopus) breeding den from the southern Arctic tundra of Yamal Peninsula, Russia in 2007. At the same time, as a current range retraction of the original inhabitant of the circumpolar tundra zone the arctic fox is going on, the red fox is expanding their range from the south into arctic habitats. Thus, within large parts of the northern tundra areas the two species are sympatric which gives opportunities for direct interactions including interference competition. However, direct first-hand observations of such interactions are rare, especially in the Russian Arctic. In the present study, we observed one red fox taking over an arctic fox breeding den which resulted in den abandonment by the arctic fox. On July 19, eight arctic fox pups were observed on the den before the red fox was observed on the same den July 22. The pups were never seen at the den or elsewhere after the red fox was observed on the den for as long as we stayed in the area (until August 10). Our observation supports the view that direct interference with red fox on breeding dens may contribute to the range retraction of arctic foxes from the southern limits of the Arctic tundra in Russia. [ABSTRACT FROM AUTHOR]

We examined how large seasonal influxes of migratory prey influenced population dynamics of arctic foxes and how this varied with fluctuations in small mammal (lemming and vole) abundance-the main prey of arctic foxes throughout most of their range. Specifically, we compared how arctic fox abundance, breeding density and litter size varied inside and outside a large goose colony and in relation to annual variation in small mammal abundance. Information-theoretic model selection showed that (1) breeding density and fox abundance were 2-3 times higher inside the colony than they were outside the colony and (2) litter size, breeding density and annual variation in fox abundance in the colony tracked fluctuations in lemming abundance. The influence of lemming abundance on reproduction and abundance of arctic foxes outside the colony was inconclusive, largely because fox densities outside the colony were low, which made it difficult to detect such relationships. Lemming abundance was, thus, the main factor governing reproduction and abundance of arctic foxes in the colony, whereas seasonal influxes of geese and their eggs provided foxes with external subsidies that elevated breeding density and fox abundance above that which lemmings could support. This study highlights (1) the relative importance of migratory prey and other foods on the abundance and reproduction by local consumers and (2) how migratory animals function as vectors of nutrient transfer between distant ecosystems such as Arctic environments and wintering areas by geese thousands of kilometres to the south. [ABSTRACT FROM AUTHOR]

In July 2008 we outfitted reproductively active adult arctic foxes with satellite tracking collars on Bylot Island, Nunavut, Canada and recorded their movements over a complete annual cycle. We present the tracking data from two individuals, one female and one male, who traveled extensively from February to July 2009, covering minimum distances of 4,599 and 2,193 km, respectively. We recorded high and sustained travel rates on both land and sea ice that reached 90 km/day for the female and 88 km/day for the male. Our data confirm that arctic foxes can move extensively and demonstrate sustained travel rates that are 1.5 times those previously measured for the species. Our study is the first presenting detailed year-round satellite tracking of adult arctic foxes and has implications for our understanding of navigational abilities, foraging ecology, trophic interactions with lemming populations, and genetic population structure of arctic foxes. [ABSTRACT FROM AUTHOR]

The extensive use of sea-ice by three arctic foxes ( Alopex lagopus) in northern Alaska was documented using satellite telemetry during the winter of 2005–2006. Here we present the first detailed data on movements of individual foxes while on the sea-ice. Two juvenile males and one juvenile female traveled long distances (904, 1,096, and 2,757 km) and remained on the sea-ice for extended periods of time (76, 120, and 156 days). Average distances traveled per day ranged from 7.5 to 17.6 km and foxes achieved maximum rates of travel of up to 61 km/day. These findings verify the use of sea-ice by arctic foxes and raise concerns that the diminishing arctic ice cover may negatively impact populations by limiting access to marine food sources. [ABSTRACT FROM AUTHOR]

We examined 83 arctic fox ( Alopex lagopus) dens on Bylot Island (Canada) during the summers of 2003–2005, to determine how arctic foxes select a denning site among potential sites, and a breeding den among existing dens. We compared denning sites to random locations in a 425 km2 study area (landscape scale) and to other potential denning sites in a 100 m radius (local scale). Dens were located on mounds or in slopes and were closer to streams than expected. Sites with low snow cover in spring, high ground temperature, high depth to permafrost, and steep and southerly exposed slopes were preferred. Of the 83 dens, 27 were used at least once for reproduction from 2003 to 2005. We show with a resource selection function analysis that an attractive force (distribution of food resources) and an apparently repulsive one (presence of other dens in the vicinity) affected selection of dens for reproduction. We generate testable hypotheses regarding the influence of food and social factors on the denning ecology of arctic foxes. [ABSTRACT FROM AUTHOR]

We describe the manifestations and occurrence of hypotrichosis in arctic foxes and compare it to the Samson character in red foxes. During 1979–2005, we collected carcasses of both normal and hypotrichotic arctic foxes from foxhunters in Iceland for macroscopic and microscopic examination and study of demography. We obtained live pups for breeding and transmission experiments in captivity during 1985–1992. Placental scar counts showed that hypotrichotic vixens were more fertile than normal vixens and generally all their pups were hypotrichotic. Fertility in hypotrichotic vixens was positively correlated with winter air temperature but not in normal vixens. Hypotrichotic males were less likely to breed than normal males and probably had a higher mortality rate than either hypotrichotic females or normal foxes. Hypotrichosis can be transmitted between adult foxes. Microscopic examination revealed prominent chronic inflammation of the dermis in hypotrichotic specimens, degenerative changes, vacuolisation and necrosis of hair follicles. Hypotrichosis persists in coastal areas with mild winters and may become more common with global warming. [ABSTRACT FROM AUTHOR]

Metabolic rates of four resting, post-absorptive male adult summer- and winter-adapted captive arctic foxes ( Alopex lagopus) were recorded. Basal metabolic rates (BMR) varied seasonally with a 36% increase from winter to summer, while body mass was reduced by 17% in the same period. The lower critical temperature ( T 1c) of the winter-adapted arctic fox was estimated to −7°C, whereas T lc during summer was 5°C. The similarity of these values, which are much higher than hitherto assumed (e.g. Scholander et al. ), is mainly due to a significantly ( P<0.05) lower BMR in winter than in summer. Body core (stomach) temperature was stable, even at ambient temperatures as low as −45°C, but showed a significant ( P<0.05) seasonal variation, being lower in winter (39.3±0.33°C) than in summer (39.8±0.16°C). The thermal conductivity of arctic fox fur was the same during both seasons, whereas the thermal conductance in winter was lower than in summer. This was reflected in an increase in fur thickness of 140% from summer to winter, and in a reduced metabolic response to ambient temperatures below T lc in winter. Another four arctic foxes were exposed to three periods of forced starvation, each lasting 8 days during winter, when body mass is in decline. No significant reduction in mass specific BMR was observed during the exposure to starvation, and respiratory quotient was unchanged at 0.73±0.02 during the first 5 days, but dropped significantly ( P<0.05) to 0.69±0.03 at day 7. Locomotor activity and body core (intraperitoneal) temperature was unaltered throughout the starvation period, but body mass was reduced by 18.5±2.1% during these periods. Upon re-feeding, locomotor activity was significantly ( P<0.05) reduced for about 6 days. Energy intake was almost doubled, but stabilised at normal levels after 11 days. Body mass increased, but not to the level before the starvation episodes. Instead, body mass increased until it reached the reduced body mass of ad libitum fed control animals. This indicates that body mass in the arctic fox is regulated according to a seasonally changing set point. [ABSTRACT FROM AUTHOR]

Arctic fox (Alopex lagopus) numbers vary greatly, with cyclic fluctuations often associated with fluctuations in microtine rodents. However, in areas where small prey mammals are absent, such as Iceland and Svalbard, such cyclic fluctuations are lacking. Annual fluctuations in the density of the arctic fox population on the Brøggerhalvøya peninsula and Kongsfjorden region on Svalbard, Norway, were studied from 1990 to 2001 by using indices of fox abundance. All indices showed similar trends; fox numbers were low in 1990, increased until 1995 whereupon they decreased sharply, before increasing again and levelling off in 2001. Increasing numbers of foxes during the first part of the study paralleled increasing numbers of Svalbard reindeer (Rangifer tarandus platyrhynchus) carcasses in winter and increasing numbers of nesting barnacle geese (Branta leucopsis) in summer. This study shows that the number of arctic foxes varies greatly even in areas without fluctuating microtine rodents. [ABSTRACT FROM AUTHOR]

We examined the relationship between the distribution of arctic fox dens and the occurrence of rugged terrain on Svalbard, Norway, using indices of terrain ruggedness (TRI) based on contour characteristics from topographic maps in 240 grid cells, each 4 km2. The distribution of rugged terrain co-varied with occurrence of arctic fox dens. Moderately rugged terrain (TRI=1.5–3.0) constituted only 21% of the total study area, but contained 77% of all natal dens recorded in the study area. Large clusters (8–36 km2) of moderately rugged terrain were generally preferred for location of den sites compared to smaller scattered clusters of rugged terrain. The importance of rugged terrain is discussed in relation to snow cover, exposure, soil conditions and distribution of prey species. This simple and non-invasive analysis of terrain ruggedness may be used to predict the distribution of potential arctic fox denning areas across landscapes. [ABSTRACT FROM AUTHOR]