Geographic and ecological variation in breeding parameters of insectivorous birds throughout the western Palaearctic

Abstract

The present study shows variation in some breeding parameters (laying date, clutch size) in relation to geographical coordinates (latitude, longitude), habitat, elevation and habitat type in insectivorous and hole-nesting passerine of European woodlands. The Great Tit (Parus major) was used as a model species. Laying date, at the population level, was not affected by habitat type, and did not show any relationship with longitude and elevation. Laying date showed a significant quadratic relationship with latitude, with the earliest values in central Europe. On the other hand, clutch size at the population level significantly differed among habitat type (large clutches being laid in deciduous forests), showed a positive and negative relationships with longitude and elevation, respectively. Mean clutch size showed a quadratic relationship with latitude, with the highest values at about 55 to 60ºN. In the present study, the main hypotheses proposed to explain these patterns found on the breeding parameters of passerines in the Western Palaearctic are discussed.