Vole abundance and reindeer carcasses determine breeding activity of Arctic foxes in low Arctic Yamal, Russia

Abstract

Background: High latitude ecosystems are at present changing rapidly under the influence of climate warming, and specialized Arctic species at the southern margin of the Arctic may be particularly affected. The Arctic fox (Vulpes lagopus), a small mammalian predator endemic to northern tundra areas, is able to exploit different resources in the context of varying tundra ecosystems. Although generally widespread, it is critically endangered in subarctic Fennoscandia, where a fading out of the characteristic lemming cycles and competition with abundant red foxes have been identified as main threats. We studied an Arctic fox population at the Erkuta Tundra Monitoring site in low Arctic Yamal (Russia) during 10 years in order to determine which resources support the breeding activity in this population. In the study area, lemmings have been rare during the last 15 years and red foxes are nearly absent, creating an interesting contrast to the situation in Fennoscandia.

Results: Arctic fox was breeding in nine of the 10 years of the study. The number of active dens was on average 2.6 (range 0-6) per 100 km² and increased with small rodent abundance. It was also higher after winters with many reindeer carcasses, which occurred when mortality was unusually high due to icy pastures following rain-on-snow events. Average litter size was 5.2 (SD = 2.1). Scat dissection suggested that small rodents (mostly Microtus spp.) were the most important prey category. Prey remains observed at dens show that birds, notably waterfowl, were also an important resource in summer.

Conclusions: The Arctic fox in southern Yamal, which is part of a species-rich low Arctic food web, seems at present able to cope with a state shift of the small rodent community from high amplitude cyclicity with lemming dominated peaks, to a vole community with low amplitude fluctuations. The estimated breeding parameters characterized the population as intermediate between the lemming fox and the coastal fox ecotype. Only continued ecosystem-based monitoring will reveal their fate in a changing tundra ecosystem.

Keywords: Diet; Food web; Numerical response; Reindeer carcasses; Small rodent community; Vole cycle; Vulpes lagopus.

Fig. 1

Map of the Erkuta tundra monitoring site in southern Yamal, Russia. The inset indicates the location of the area in the western Eurasian Arctic (represented by the red star) and shows the five bioclimatic subzones of the Arctic according to [2]. Subzones A–C represent the high Arctic whereas subzones D and E represent the low Arctic. The hatched ellipses show the three replicate areas (units), where herbivore faeces counts and small rodent trapping were carried out. All fox dens are shown. Red dots represent dens where pups have been observed during the study period, and red lines link dens between which fox families have moved. The green lines show the extent of the study area in the first year of the study (2007) and the maximal extent of the study area. Note, however, that in most years the area actually surveyed was somewhat less than this maximal area

Fig. 2

Dynamics of main herbivores from 2007 to 2016 at Erkuta, southern Yamal. a Number of voles and lemmings caught on trapping quadrats per 24 trap nights. b Occurrence of mountain hare and willow ptarmigan faeces estimated as the number of small plots surrounding a quadrat where faeces were recorded (max eight small plots). For each trapping/faeces counting session (second part of June and August each year except in 2007, where one observation was carried out in July, in 2009 for faeces counts and in 2016, when only the June trapping and counts were carried out), mean results for all habitats are shown with standard error. Lines join the estimates from June

Fig. 3

Number of active dens and litter size of Arctic foxes at Erkuta, southern Yamal. Number of active Arctic fox dens (breeding) per 100 km² and mean minimum number of pups with standard errors observed between 2007 and 2016 at Erkuta. The numbers on the bars show the number of active dens per year (lower) and the number of dens where a minimum number of pups could be determined either by proper observation or with automatic cameras (upper)

Fig. 4

Proportion of active dens in relationship to small rodent abundance and availability of reindeer carcasses. Observed proportion of active Arctic fox dens (breeding) in relation to the small rodent trapping index in June for years with and without high availability of reindeer carcasses for the years 2007 to 2016. Open symbols refer to 2007 and 2014, the years with high availability of reindeer carcasses, whereas filled symbols refer to the other years. Lines show the predicted probability for a den to be active as estimated from a generalized linear mixed model (additive effect of small rodents and reindeer on the logit scale), and polygons show 95% confidence intervals. The thin line and doted polygon refer to years with high availability of reindeer carcasses whereas the thick line and grey polygon refer to the other years

Fig. 5

Diet of Arctic foxes at Erkuta, southern Yamal. a Percentage of each prey category identified from scat dissection. In 2007 percentage of dry weight was estimated, whereas in 2013 and 2014 percentage of volume was estimated. These estimates can thus not be directly compared. b Proportion of den visits in the years 2010–2016 during which remains of different categories of prey were recorded. Number of visits per year are given in parentheses. c Polygons surrounding the stable isotope signatures of Arctic fox winter fur are shown in different colours for each year (i.e. the year during which the fur was growing; sample sizes in parentheses). Values have been corrected for isotopic discrimination according to Lecomte et al. [49]. Average signatures of main prey groups are shown with standard deviations: Dt, collared lemming; Mg, narrow-sculled vole; Mm and Mr, Middendorff’s vole and red vole; Oz, muskrat; Rt, domestic reindeer; Ll, willow ptarmigan; Lt, mountain hare; wp, waders and passerines; wt, waterfowl