The dynamics of hazel grouse (Bonasa bonasia L.) occurrence in habitat fragments

The aim of this study was to evaluate the effects of habitat fragment size and isolation on the dynamics of hazel grouse (Bonasa bonasia L.) occurrenc e. Habitat fragments surrounded by nonhabitat coniferous forest, in an inte nsively managed forested landscape, were censused during seven seasons. Non e of the 33 habitat fragments were occupied in all seven seasons and 7 were never occupied. Turnover occurred in 79% of the habitat fragments. The mos t common occupation of a habitat fragment was by only one hazel grouse male (84%). Thus, the dynamics of hazel grouse occurrence in the habitat fragme nts was basically monitored on the scale of individuals. Large and less iso lated habitat fragments with a high amount of cover were occupied significa ntly more often than small, isolated fragments. The effect of size appeared most clearly when analyzing the total number of hazel grouse occupying a h abitat fragment. The appearance of hazel grouse in the habitat fragments wa s best explained by the amount of cover, distance to the nearest suitable h abitat, and size of the habitat fragment. The effects of interfragment dist ance on the occurrence and appearance of hazel grouse implies that the habi tat has become functionally disconnected for hazel grouse and suggests that the amount of suitable hazel grouse habitat left in this landscape has fal len below a critical level.