Effects of habitat quality and hiking trails on the occurrence of Black Grouse (Tetrao tetrix L.) at the northern fringe of alpine distribution in Austria

The Black Grouse (Tetrao tetrix L.), listed in Annex 1 of the European Bird Directive, inhabits the vulnerable alpine treeline ecotone. Reacting sensitively to modifications of the environment, it can be regarded as an indicator species. To assess summer habitat use, we measured habitat parameters and recorded faeces (intestinal droppings) of Black Grouse on a mountain chain of the Northern Limestone Alps at the northern fringe of its distribution. In the area, the existing hiking trails are frequently used by hikers in summer. We modelled summer habitat use and included effects of hiking trails testing three different buffer radii around hiking trails (i.e., 50, 100 and 150 m); the buffer radius of 50 m significantly contributed to the final model of habitat use. Altitude, cover of grasses/herbs, canopy cover of woody plants < 5 m, canopy cover of woody plants a parts per thousand yen5 m, grazing intensity, and the interaction term cover of grasses/herbs x canopy cover of woody plants a parts per thousand yen5 m combined with presence-absence of hiking trails best predicted the occurrence of Black Grouse. Our calculations yielded lower probabilities of Black Grouse occurrence areas adjacent to hiking trails (odds of presence reduced by 93 %). Terrestrial mapping of indirect signs and the statistical model were appropriate to depict significant differences of probabilities of occurrence within and outside the buffer zone around hiking trails. Considering the habitat variables in the model, enhancing small-scale habitat heterogeneity seems to be a recommendable habitat management strategy; by creating a fine mosaic of higher woody plants, dwarf shrubs and open, grassy habitat patches, a rich supply of food and cover can be provided within short distances.