Ari Jäntti

Forest management is associated with physiological stress in an old-growth forest passerine.

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.

REPRODUCTIVE SUCCESS OF EURASIAN TREECREEPERS, CERTHIA FAMILIARIS, LOWER IN TERRITORIES WITH WOOD ANTS

Few studies have considered the effects of interspecific competition between distantly related taxa on the reproductive success of individuals. We compared the food supply, laying date, clutch size, and breeding success of a small double-brooded passerine bird, the Eurasian Treecreeper (Certhia familiaris) between territories with or without col- onies of red wood ants (Formica rufa group) during four years. Both the wood ants and Eurasian Treecreepers forage on tree trunks and utilize the same food resources. It has been shown that the wood ants are able to depress the available food supply for the treecreepers and interfere with their foraging behavior. We found that food abundance was lower in territories colonized by wood ants, and that this difference was more pronounced during the second clutches. In territories without ants, treecreepers started breeding earlier and increased the size of second clutches, whereas birds breeding in territories with ants de- creased clutch size in second breeding attempts. In addition to hatching later, nestlings in territories with ants achieved lower body mass near fledging and suffered higher mortality than nestlings in territories without ants. Consequently, double-brooded treecreeper pairs produced an average of 2.3 more fledg- lings, also of higher quality, in territories without ants than in territories with ants. There were no differences between the territory types in any measure of habitat quality other than food abundance. Our results suggest that wood ants reduce territory quality of Eurasian Treecreepers by means of food depletion and have negative effects on the breeding success of individual birds. These results show that competition between organisms in different phyla may be effective in determining the reproductive success of individuals.

Forest fragmentation is associated with primary brood sex ratio in the treecreeper (Certhia familiaris)

We studied the primary brood sex ratio of an old–growth forest passerine, the Eurasian treecreeper (Certhia familiaris), along a gradient of forest fragmentation. We found evidence that male nestlings were more costly to produce, since they suffered twofold higher nestling mortality and were larger in body size than females. Furthermore, the proportion of males in the brood was positively associated with the provisioning rate and the amount of food delivered to the nestlings. During the first broods, a high edge density and a high proportion of pine forests around the nests were related to a decreased production of males. The densities of spiders, the main food of the treecreeper, were 38% higher on spruce trunks than on pine trunks. This suggests that pine–dominated territories with female–biased broods may have contained less food during the first broods. The observation was further supported by the fact that the feeding frequencies were lower in territories with high proportions of pines. In the second broods, territories with a high forest patch density produced female–biased broods, whereas high–quality territories with a large amount of deciduous trees and mixed forests produced male–biased broods. Our results suggest that habitat quality as measured by habitat characteristics is associated with sex allocation in free–living birds.

Effects of male removal on female foraging behavior in the Eurasian treecreeper

Abstract In old, spruce-dominated forests of central Finland, Eurasian treecreepers Certhia familiaris divide their territories spatially during the breeding season. Females forage primarily on the upper parts of the tree trunks, while males use the lower parts of the tree trunks. In this study we removed males from eight territories in the early nestling period to see if the mates absence would change the foraging patterns of the resident female. Widowed females foraged at lower heights, thus behaving more like paired males. These females also spent less time on each tree and on each foraging bout than did paired females. We conclude that male removal facilitated the change in a females foraging niche and foraging time at the trees. Females may re-optimize their foraging site selection owing to the absence of dominant males and a consequent need to increase their parental care. Behavioral plasticity may be the mechanism of niche partitioning between the sexes in this species.

Behavioural responses of Eurasian treecreepers,Certhia familiaris, to competition with ants☆

Competition for a specific resource that is essential for the survival of both the competitors may be intense even between very dissimilar taxa. However, the importance of the effects caused by such interspecific competition has seldom been emphasized. These effects can appear as differences in individual foraging behaviour during the breeding season, which can result in critical variation in fitness. In this study we examined the effects of wood ants (Formica rufa group) on the abundance of other invertebrates on tree trunks and on the foraging site selection of breeding Eurasian treecreepers, which use the same habitat as wood ants. Arthropods were scarcer on the trunks with ants present; the treecreepers avoided these trunks and foraged for a shorter time on trunks with ants than on trunks without ants. We also tested experimentally the existence of competition between ants and treecreepers by comparing the foraging behaviour of breeding treecreepers on spruce trunks with ants, without ants and with experimentally reduced numbers of ants. On average arthropods were scarcest on trunks with ants present. Male treecreepers also foraged for a shorter time on spruce trunks with ants. The reduction in ant numbers allowed food resources on trunks to recover over a week and led to longer foraging times of the treecreepers on these trunks than on trunks with ants present. The longest treecreeper visits were on trunks without ants. Our results suggest that competition between two very different taxa may be effective in determining the behaviour of foraging individuals.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour

Habitat-related nest predation effect on the breeding success of the Eurasian treecreeper

Abstract We studied the impact of habitat structure on the long-term breeding success of an old-growth forest passerine the Eurasian treecreeper (Certhia familiaris) assessed over a period of 7 years in the same forest patches. Breeding success was greater less variable in areas with a high proportion of mature forest lower more variable in areas with high proportions of young sapling stands. This difference was almost exclusively due to a high degree of nest predation in patches characterized by a low proportion of mature forest. In this study nest predation explained approximately 50% of the between-year variation in breeding success. We found that in patches where the proportion of mature forest in the landscape was over 60% nest predation was considerably lower than in patches below this threshold value. Small mustelids were likely responsible for the high nest predation rate increased year-to-year variability in the breeding success of the treecreeper. Small mustelids that mainly prey on voles may following a crash in the vole population shift their diet towards alternatives such as bird nests. This can happen especially in environments with a high human impact such as in sapling areas young forests since these habitats can support high numbers of voles their predators.