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.

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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.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. 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 colonies 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 decreased 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 fledglings, 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.

We used long-term breeding data to monitor the influences of fragmentation and habitat composition at different spatial scales on the reproductive success of Eurasian Treecreepers (Certhia familiaris) breeding in nest boxes. We collected data from the same forest patches (2.7-65.1 ha in size) during seven breeding seasons. Nest predation varied considerably over the years and was the primary cause of nesting failure (mean annual rate of 21.6 ± 12.8%). Nest predation explained most of the variation in fledgling production during the study period. Landscape-level fragmentation (radius of 500 m from territory center) affected nest predation more than did fragmentation on the territory scale (radius of 200 m from territory center). In general, nest loss due to predation in fragmented landscapes (32.4%) was almost threefold that of less fragmented (12.0%) landscapes. Of the habitat variables, predation rate correlated positively with the density of edges between forest and open land and with the proportion of sapling stands on the spatial scale of 500 m around a nest. In the core area of a territory (radius of 30 m from territory center), a high density of trees increased the frequency of nest predation. Further, a high proportion of agricultural land close to a nest site increased nest losses of treecreepers, probably because of a high degree of mustelid predation. Our results showed that the spatial scale on which we examined nest predation is important and that even within moderately fragmented landscapes it is possible to detect fragmentation-related nest predation.Resumen: Utilizamos datos de largo plazo para hacer un seguimiento de los efectos de la fragmentación y composición del hábitat en diferentes escalas espaciales sobre eléxito reproductivo de Certhia familiaris en nidos de cajón. Colectamos datos de los mismos parches de bosque (2.7-65.1 ha) durante sieteépocas reproductivas. La depredación de nidos varió considerablemente a lo largo de los años y fue la causa principal del fracaso reproductivo (tasa media anual de 21.6 ± 12.8%). la depredación de nidos explicó la mayor variación en la producción de crías durante el período de estudio. La fragmentación a nivel de paisaje (radio de 500 m del centro del territorio) afectó a la depredación de nidos más que la fragmentación a escala de territorio (radio de 200 m del centro del territorio). En general, la pérdida de nidos debido a la depredación en paisajes fragmentados (32.4%) fue casi tres veces mayor que en los paisajes menos fragmentados (12%). De las variables de hábitat, la tasa de depredación se correlacionó positivamente con la densidad de los bordes entre el bosque y terrenos abiertos y con la proporción deárboles jóvenes en la escala espacial de 500 m alrededor de un nido. En elárea núcleo de un territorio (radio de 30 m del centro del territorio), una alta densidad dé arboles incrementó la frecuencia de depredación de nidos. Más aun, una alta proporción de terreno agrícola cercano a un nido incrementó las pérdidas de nidos, probablemente debido a u...