Minimum viable population size of capercaillie Tetrao urogallus: results from a stochastic model

Abstract

In order to estimate minimum area requirements for viable isolated populations of capercaillie Tetrao urogallus in Central Europe, we developed a stochastic population model. Model parameters were largely based on the results of a field study in the Bavarian Alps. Environmental fluctuations (amount of rainfall in June and July) are taken into account in the early survival of chicks. For the default parameter set, the model predicts a minimum capacity needed for viability, i.e. for the extinction risk not to exceed 1% in 100 years, of about 470 individuals. In the Bavarian Alps, this corresponds to area requirements of an isolated viable population in an order of magnitude of 250 km2. These results are, however, sensitive to small changes in model parameters such as female survival, clutch survival and chick survival. We conclude that minimum viable population size and minimum area requirements may vary considerably across the range of the capercaillie. Therefore, we plan to apply our model to different parameter sets from different regions in order to explore the range of conditions under which capercaillie populations may be viable.