Site fidelity of Svalbard polar bears revealed by mark-recapture positions

Abstract

The spring season is important to polar bears, since females with young cubs leave the maternity dens, ringed seal pupping creates a peak in prey availability, and it is the mating season. Understanding space- and resource use at this time is a key to understanding polar bear ecology. This study from Svalbard, Norway analyzed 348 measurements of spring-to-spring displacement from 220 polar bears obtained by mark-recapture sampling in the period 1987 – 2010 to assess whether the bears exhibit spring site fidelity. All age and sex classes of polar bears showed site fidelity when their movements were compared to a scenario of random movements between all capture locations. The median observed displacement for all bears was 43.0 km (bootstrapped 95% CI: 34.3 - 51.0 km), significantly smaller than the median potential displacement for random movements of 205.4 km (bootstrapped 95% CI: 205.1 - 205.6 km). Linear model analysis of all displacements showed that displacement length depended on both the age and sex of the individual. Subadult females had the longest displacements, followed by adult males and adult females. Consistent, precise site fidelity over time was only displayed by a subset of females. When only the first movement of each bear was included, the effects of age and sex in the linear model were less pronounced, and the difference between adult males (linear model estimate: 50.0 km) and adult females (40.7 km) was not significant. These findings support previous reports in the literature comparing movement patterns of males and females in other parts of the Arctic. Sufficient data to conclusively evaluate subadult movement patterns is still lacking. Overall similarities in site fidelity of adult males and females indicate that findings based on telemetry of females may be relatively representative of the whole adult Barents Sea population.