Colonization history and noninvasive monitoring of a reestablished wolverine population

The southern Norwegian wolverine (Gulo gulo) population was considered functionally extinct in the 1960s but has partly recovered in recent years. Proper management of this population is highly dependent on reliable estimates of critical population parameters such as population size, sex ratio, immigration rate, and reproductive contribution from immigrants. We report on a large-scale population monitoring project assessing these parameters through genetic tagging of individuals, with feces as the source of DNA. Sixty-eight different individuals were detected among 147 successfully genotyped samples collected in 2000 and 2001. Sixty of these individuals were represented in the 2001 sample, which may be considered a minimum estimate of the population size. Almost 50% of these animals were sampled only once, however, indicating that the true population size may be markedly higher. Accordingly, a capture-recapture estimate based on the observed resampling rates suggested a population size of 89 wolverines (95% confidence interval [CI] = 74-104), which is approximately 35% higher than an estimate of 64 obtained from the number of active natal dens (95% CI = 46-95; p = 0.08). Indirect estimates of dispersal distances inferred from mother-offspring relationships suggested that wolverine males have the ability to disperse up to 500 km, a distance exceeding anything previously reported in the literature. Dispersal distances of more than 100 km were detected for females. Bayesian clustering analysis and subsequent assessment of individual relationships suggest that immigrants from northern Scandinavia have contributed and still contribute to the southern Norwegian gene pool, counteracting genetic erosion and reducing the risk of inbreeding depression. Additional sampling efforts will be undertaken during the coming years to allow for observations of population trends, immigration rate, and reproductive variance among individuals. Such data will provide an important basis for the design of an appropriate conservation plan for this small and vulnerable population.