FOREST FRAGMENTATION DUE TO AGRICULTURE AFFECTS THE REPRODUCTIVE SUCCESS OF THE GROUND-NESTING BLACK GROUSE TETRAO TETRIX

We used data from the Finnish wildlife triangle censuses (1989-92) to test the prediction that the reproductive success of ground nesting bi rd species is lowered in forest landscapes fragmented by the occurrenc e of agricultural land, presumably as a consequence of increased densi ties of generalist predators. Our study was based on 201 wildlife tria ngles located in central Finland (total length 2412 km). As expected, the proportion of black grouse hens with a brood in August decreased r elative to the increasing proportion of agricultural land in a landsca pe (100 km(2)). However, on a smaller spatial scale (10.8 km(2)), the probability of an observed hen being with a brood was higher in the vi cinity of fields. This finding may be explained by differences in habi tat selection between hens with a brood and those without a brood. We did not find any negative effect of landscape composition on brood siz e. We conclude that increased predation pressure in forest landscapes fragmented by agriculture affects nesting success, but not the surviva l of black grouse chicks after hatching. Our results also emphasize th e importance of spatial scale in studies of landscape ecology.