Forest fragmentation due to agriculture affects the reproductive success of the ground‐nesting black grouse Tetrao tetrix

Abstract

We used data from the Finnish wildlife triangle censuses (1989‐92) to test the prediction that the reproductive success of ground‐nesting bird species is lowered in forest landscapes fragmented by the occurrence of agricultural land, presumably as a consequence of increased densities of generalist predators Our study was based on 201 wildlife triangles located in central Finland (total length 2412 km) As expected, the proportion of black grouse hens with a brood in August decreased relative to the increasing proportion of agricultural land in a landscape (100 km2) However, on a smaller spatial scale (10 8 km2), the probability of an observed hen being with a brood was higher in the vicinity of fields This finding may be explained by differences in habitat selection between hens with a brood and those without a brood We did not find any negative effect of landscape composition on brood size We conclude that increased predation pressure in forest landscapes fragmented by agriculture affects nesting success, but not the survival of black grouse chicks after hatching Our results also emphasize the importance of spatial scale in studies of landscape ecology