Solberg, H., Bellemain, E., Drageset, O.M., Taberlet, P., Swenson, J.E. 2006. An evaluation of field and genetic methods to estimate brown bear (Ursus arctos) population size. Biological conservation 128, 158-168.

Estimates of population size and density are essential for successful management and conservation of any species. Although there are a variety of methods available for estimating abundance and density of populations, most studies rely on only one estimator and very few studies have compared and critically evaluated the adequacy and the cost of these methods. We used the brown bear (Ursus arctos) in south-central Sweden to compare the performance of three different methods of estimating population size, including methods based on conventional field data as well as on non-invasive genetic data. The method based on observations of females with cubs underestimated the true population size, as the estimates were below the number of unique genotypes determined from fecal data inside the study area. The genetic method using the closed population MARK estimator, as recommended in a previous study, seemed to perform the best. We conclude that approximately 223 (188-282) bears were present in our 7,328 km_ study area during 2001 and 2002 and suggest that this hunted brown bear population has been relatively stable for about ten years. The non-invasive genetic method was less expensive than the most reliable traditional field method, and preferable from an ethical point of view. We recommend that future studies should aim at collecting 2.5 to 3 times the number of faecal samples as the “assumed” number of animals.

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