Natural factors or human disturbance: What shapes the occurrence of black grouse Lyrurus tetrix on the edge of its continuous range?

The black grouse belongs to a group of birds sensitive to environmental changes. A decrease in its numbers may signal the deteriorating habitat condition. In this study, we analyzed the impact of a number of predictors on the species' occurrence in one of its last Central European, mountainous refuge - the Polish Tatra Mountains. The study aimed to understand the land use of the species and identify the most important factors for its survival. Our results indicate the predominance of land cover over the other factors studied. Particularly, the presence of dwarf shrubs promoted the occurrence of black grouse. It showed a positive correlation with vegetation providing food and lekking sites and land cover by forest in the surroundings. A negative relationship was found with bare rock cover and high tourist pressure around the occurrence sites. Human disturbance had a negative impact on the species' occurrence, but it was less significant than habitat quality. However, it may be considered a habitat-fragmenting factor. Our results highlight the need to consider a large spatial scale when studying the effects of biotic and abiotic factors on a declining population, which is particularly important on the edge of the species’ continuous range. For conservation, it would also be optimal to incorporate our results along with data on reproductive success and the impact of climate change on shaping the local biotope.