In Fennoscandia, two hypotheses predict how predation on nests and broods of forest grouse may be connected to human-induced changes in landscape composition. First, predation rates are higher in forest areas fragmented and intermixed with agricultural land due to higher generalist predator densities supported by the agricultural matrix. Second, within forest land, fragmentation of mature forest due to clear-cuttings has been suggested to increase mammalian predator densities by increasing suitable grass-dominated habitats for Microtus. Using Finnish wildlife triangle census data (1989-94), the locations of 2,267 black grouse Tetrao tetrix and 1,060 capercaillie T. urogallus females after the breeding seasons (mid-August) were combined with land-use and forest resource data using GIS in two study areas (both 450 km?) in southern and northern Finland. Land-use and forest resource data (pixel size 25 m) were based on classification of Landsat TM 5 images with field plot network of Finnish forest inventories and digital masks of non-forest lands. After reclassifying landscape data to: 1) water area, 2) agricultural land, 3) clear-cuttings and plantations, 4) young forest, and 5) closed canopy forest, circular landscapes around locations of grouse females with six different radii (500, 1,000, 1,500, 3,000, 5,000, and 10,000 m) were formed, and the proportions of different habitat types were computed with FRAGSTATS. The probability of an observed grouse hen being with a brood was positively associated with the proportion of closed canopy forest in the landscape in both study areas. In the south, the effect was strongest with the radius of 3,000 m, and in the north with the largest radius (10,000 m), whereas in both areas the effect was weakest, although significant, with the shortest landscape radius (500 m). Among other habitat types, depending on study area and landscape radii, the increasing proportion of young forest, clear-cuttings, plantations, and agricultural land affected negatively the proportion of hens with a brood. Landscape composition was not correlated with brood size of grouse. Breeding success of forest grouse was landscape dependent in Fennoscandia, and breeding success was negatively affected by the fragmentation of closed canopy forests. A negative correlation between red fox Vulpes vulpes densities and proportions of closed-canopy forest in the landscape was also found. Brood size was not affected by landscape composition, thus, predation causes total losses of either nests or broods. Lowered breeding success of grouse as a result of forest fragmentation is most likely one of the reasons for declines in grouse populations during past decades in Fennoscandia.

Key words: Fennoscandia, forest grouse, fragmentation, nest success, predation, survival

Sami Kurki, Laboratory of Ecological Zoology, Department of Biology, FIN-20014 University of Turku, Finland
Ari Nikula, Finnish Forest Research Institute, Rovaniemi Research Station, P.O. Box 16, FIN-0-96301 Rovaniemi, Finland
Pekka Helle, Finnish Game and Fisheries Research Institute, Meltaus Game Research Station, FIN-97340 Meltaus, Finland
Harto Lind?n, Finnish Game and Fisheries Research Institute, P.O. Box 6, FIN-00721 Helsinki, Finland