Pål Prestrud

Fat deposition and seasonal variation in body composition of arctic foxes in Svalbard

We studied the seasonal variation in body composition of arctic foxes (Alopex lagopus) to determine the adaptive significance of fat deposition in this species. Homogenates of 75 minced fox carcasses were analyzed. On a large sample of animals trapped in 1982-89, the thickness of subcutaneous fat was measured, and the amount of fat was indexed subjectively. Fat was deposited both subcutaneously and viscerally in September-October, and it reached a maximum of about 20% of the skinned carcass mass in November. The amount of fat deposited did not decline between November and March of any year. The fat deposits were depleted from March through May, reaching about 6% of the carcass mass by the summer. Fifteen percent of the trapped foxes did not have any subcutaneous or visceral fat deposits in winter

Local variation in arctic fox abundance on Svalbard, Norway

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.

Home range and movements of Arctic foxes Alopex lagopus in Svalbard

SummaryMovements and home ranges of arctic foxes Alopex lagopus were studied in two regions of Svalbard by means of radio tracking (n= 17), ear tagging (n= 192) and visual observations. The movements of radio collared foxes were highly variable, and most foxes roamed over wide areas at least during periods of the year. Home range size was estimated for 11 foxes when more stationary and for three other less stationary foxes, and were in the range 5–120km2. During non-stationary periods several foxes roamed over areas 500–1000 km2 or more. These movements may more correctly be classified as nomadic, and should not be termed home ranges. Only 3 of 12 radio collarec. foxes that disappeared from an area, returned later. Seven of the 17 foxes were relocated to the same area in more than one season. Overlap of home ranges was extensive, even more so when a number of non-tagged foxes in the regions were included. The heavier juveniles and adults were more sedentary than those of weight lower than median.

Reproductive responses to spatial and temporal prey availability in a coastal Arctic fox population

1. Input of external subsidies in the Arctic may have substantial effects on predator populations that otherwise would have been limited by low local primary productivity. 2. We explore life-history traits, age-specific fecundity, litter sizes and survival, and the population dynamics of an Arctic fox (Vulpes lagopus) population to explore the influence of the spatial distribution and temporal availability of its main prey; including both resident and migrating (external) prey resources. 3. This study reveals that highly predictable cross-boundary subsidies from the marine food web, acting through seasonal access to seabirds, sustain larger local Arctic fox populations. Arctic fox dens located close to the coast in Svalbard were found to have higher occupancy rates, as expected from both high availability and high temporal and spatial predictability of prey resources (temporally stable external subsidies). Whereas the occupancy rate of inland dens varied between years in relation to the abundance of reindeer carcasses (temporally varying resident prey). 4. With regard to demography, juvenile Arctic foxes in Svalbard have lower survival rates and a high age of first reproduction compared with other populations. We suggest this may be caused by a lack of unoccupied dens and a saturated population.

Growth, Size, and Sexual Dimorphism in Arctic Foxes

Increase in weight and length of lower leg of Arctic foxes ( Alopex lagopus ), captured in Svalbard, Norway, from 25 days of age to maturity were described using the Gompertz growth model. The asymptotic values of length of calf were 14.3 cm in females and 15.2 cm in males. The asymptotic values of body weight were 3,102 g in females and 3,583 g in males. Males grew larger than females mainly by growing for a longer time. Absolute growth rates were ca. 50% greater than were predicted from the established regression between growth rate and body weight in carnivores. Growth ceased when foxes were 6–7 months of age. Differences in body mass and lengths of body, tail, and calf among juvenile, yearling, and adult foxes caught in December–March were not significant. From measurements on a sample of trapped foxes ( n = 848), males were significantly larger than females in body weight (19%) and lengths of body (4%), calf (6%), and tail (4%). The high rate of growth for Arctic foxes is consistent with the observed rates of other canids and, consequently, is not an adaptation to a living in a more seasonal, Arctic environment. Sexual dimorphism was documented for Arctic foxes.

Spatial Distribution of Echinococcus multilocularis, Svalbard, Norway

In Svalbard, Norway, the only intermediate host for Echinococcus multilocularis, the sibling vole, has restricted spatial distribution. A survey of feces from the main host, the arctic fox, showed that only the area occupied by the intermediate host is associated with increased risk for human infection.

Terrain structure and selection of denning areas by arctic foxes on Svalbard

Abstract 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.

Fat indices of arctic foxes Alopex lagopus in Svalbard

We determined the validity of water content, rump fat thickness, a subjective fat index, a kidney fat index, and an index based on total body weight (TBW) and the hind foot length (HFL) in order to predict lipid content of arctic foxes Alopex lagopus. The total fat content was either determined by extracting lipid from minced carcasses (N = 75) or by dissecting all visible adipose tissue (N = 35). Water content and rump fat thickness proved to be the best predictors of fat content in arctic foxes. The ratio TBW/HFL was also a reliable index and should be a convenient and practicable way of estimating the condition of live foxes. A subjective fat index could be applied when divided into three categories, whereas the kidney fat index was not a reliable predictor of lipid content of arctic foxes.