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 studied nest predation pressure on birds along an urban gradient in urban parks in three Finnish towns. Artificial ground nests with Japanese Quail (Coturnix coturnix japonicus) eggs were depredated more in the urban area than in the adjacent forest area. Within each town, the nest predation rate was higher in the town center than in the less urbanized area of detached houses. Predation rates did not vary from year to year or between study towns. Abundances of generalist avian predators were higher in the town center than in the area of detached houses and in the surrounding forest area. Most of the nests in the town center were destroyed by avian predators. Predation rate of artificial nests in each of the town areas was higher in managed parks than in unmanaged parks, presumably due to the less dense vegetation in the managed than the unmanaged parks. A test involving covering nests revealed that artificial nests covered by adjacent vegetation survived better than nests with less cover. In our study, artificial nest loss reflected the distribution of avian nest predators. Ground nesters were present at lower abundances in areas where concealing vegetation was missing and avian nest predation was high. Apparently, nest predation is one of the several possible mechanism affecting urban bird assemblages.

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.

The risk to passerine birds of predation by the Sparrowhawk (Accipiter nisus) was analyzed with respect to differences in plumage brightness, body mass, and density of prey species, while taking into account phylogenetic relatedness of species. Data were collected from published sources in five separate areas along a south–north geographical gradient in Finland and consisted of 2214 prey remains collected from Sparrowhawk nests. Prey plumage brightness was the most important factor determining vulnerability to predation. In adults, male brightness was more important than female brightness in explaining prey vulnerability. Prey abundance did not affect the relationship between predation vulnerability and plumage brightness, because both rare and common species with bright plumage suffered higher predation. Prey species with large body mass were more vulnerable to predation in northern Finland, suggesting that in northern harsh conditions, Sparrowhawks may prefer large prey in order to fulfill their daily energy requirements. Our analyses provide evidence that predation may impose viability costs on sexually selected traits such as plumage brightness and body size.

Several aspects of the life history of reindeer (Rangifer tarandus) are related to the nutritional condition of the animals. Moreover, compensatory growth and fattening in summer decreases with age. The interaction of tooth wear and the standing crop of lichens on age-related variation in body size and tissue reserves was examined to evaluate the proximate causes of density-dependent food limitation on life history parameters in female reindeer. Studies in nine semi-domesticated free-ranging reindeer herds showed that molar height depended on the mean standing crop of terrestrial lichens in winter habitats. The extent of tooth wear had the strongest effect on body reserves among the oldest females (11-14 years). This indicates that severe tooth wear limits the animals´ ability to process food efficiently and, hence, to maintain their body reserves. Both tooth wear and the biomass of lichens influenced body mass in old females, probably because on heavily exploited winter ranges reindeer had to use higher proportions of lower-ranking coarser foods, especially dwarf shrubs.