We examined the breeding success of forest grouse in relation to anthropogenic forest fragmentation in Finland. Employing Geographic Information Systems (GIS) and grouse data derived from Finnish wildlife triangle censuses conducted during 1989–1994, we combined the locations of 2267 Black Grouse (Tetrao tetrix) and 1060 Capercaillie (T. urogallus) females after the breeding season in mid‐August with landscape data. The indicators of breeding success were the proportion of grouse hens with a brood and brood size. Two study areas (each 45 000 km2) in the boreal zone were selected for investigation. The breeding success of grouse was negatively correlated with both fragmentation of forest area per se by farmland and the decreasing proportion of older forest as a result of clear‐cutting. The extent of landscape accounting best for variation in nesting success was an order of magnitude larger (∼100 km2) than the area most probably used by a grouse female and her brood during the summer, which suggests that landscape‐scale factors may override local factors such as track size and distance from edge. The proportion of grouse hens with a brood was lower in heavily fragmented landscapes than in more continuous forest landscapes whereas only minor differences in brood size were detected. We suggest that the most likely cause of the observed spatial correlation was higher nest predation by generalist predators in fragmented forest landscapes. The effects of landscape composition on the breeding success of grouse were more marked in northern than in southern Finland, probably because predator populations are more food‐regulated in the north. The diminished breeding success of forest grouse as a result of increased forest fragmentation is a probable cause of population declines in forest grouse species during the past decades in Fennoscandia.

Summary 0[ The e}ects of human!caused fragmentation of boreal forest on the abundance of red fox Vulpes vulpes L[ and pine marten Martes martes L[ were studied by combining the Finnish wildlife!triangle snow!track data "0889Ð83# with land!use and forest resources data employing the GIS[ Two study areas "each 34 999 km 1 # located in northern and southern Finland were selected for the investigation[ 1[ The extent of landscape that best explained predator abundance "tracks per 09 km 13 h −0 # was the same "about 099 km 1 # in both species and study areas[ 2[ The decreasing proportion of older forest and the increasing proportions of young forest and agricultural land in the landscape positively a}ected track density of red fox[ The relationship between agricultural land and fox abundance\ however\ was characterized by a convex curve peaking at 19Ð29) of agricultural land[ With the habitat classi_cation used\ landscape composition explained 15) and 00) of the spatial variation in fox abundance in the northern and southern study area\ respec! tively[ 3[ The relationship between landscape composition and pine marten abundance was not as clear as in that of red fox[ Landscape composition explained 09) and 5) of spatial variation in pine marten abundance in the northern and southern study area\ respectively[ In both areas a positive impact occurred with the increasing proportion of young forest in the landscape\ but in the northern area the negative e}ect of increasing proportion of agricultural land was dominant[ 4[ The abundances of red fox and pine marten were not negatively correlated\ indi! cating that competition or intraguild predation by red fox do not determine abundance of pine marten on a landscape scale[ 5[ A general increase in predation pressure by generalist predators in fragmented forest landscapes has been an intensively discussed conservation problem during recent years[ We conclude that the red fox is a species potentially able to cause elevated predation pressure in boreal landscapes fragmented by human activities\ but that the evidence against the pine marten is weaker[ Key!words] Finland\ forest fragmentation\ geographical information systems\ land! scape ecology\ predation[ Journal of Animal Ecology "0887# 56\ 763Ð775

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We investigated how physiological stress in an area-sensitive old-growth forest passerine, the Eurasian treecreeper (Certhia familiaris), is associated with forest fragmentation and forest structure. We found evidence that the concentrations of plasma corticosterone in chicks were higher under poor food supply in dense, young forests than in sparse, old forests. In addition, nestlings in large forest patches had lower corticosterone levels and a better body condition than in small forest patches. In general, corticosterone levels were negatively related to body condition and survival. We also found a decrease in corticosterone levels within the breeding season, which may have been a result of an increase in food supply from the first to the second broods. Our results suggest that forest fragmentation may decrease the fitness of free-living individual treecreepers.

We manipulated the primary brood size of Eurasian treecreepers (Certhia familiaris) breeding in different sized forest patches (0.5-12.8 ha) in moderately fragmented landscapes. We examined the effects of brood size manipulation (reduced, control, enlarged) and forest patch size on physiological stress (heterophillymphocyte ratios; H/L), body condition and cell-mediated immunocompetence (phytohaemagglutinin test). Nestlings' H/L ratios were negatively related to forest patch area in control and enlarged broods, whereas no effects were found in reduced broods. The effects of forest patch area were strongest in enlarged broods, which had, in general, twofold higher H/L ratios than control and reduced broods. The elevated H/L ratios were positively related to nestling mortality and negatively correlated with bodycondition indices suggesting that the origin of stress in nestlings was mainly nutritional. Cell-mediated immunity of nestlings was not related to brood manipulation or to forest patch size. Also, the H/L ratios of adults were not related to brood manipulation or forest patch size. In addition, parental H/L ratios and body condition were not related to nestling H/L ratios. Our results suggest that during the breeding period the deleterious effects of habitat loss are seen explicitly in growing young.