Abstract

Large-scale spatial gradients of environmental conditions shape organisms, populations and ecosystem. Even though environmental gradients are a key research theme in macro-ecology and biogeography, the effects of large-scale, east-west, environmental gradients are largely overlooked compared with north-south gradients. Our study focused on feather moult, an important and energy demanding process in birds. By comparing Eastern and Western Palearctic populations of 21 species, we found that passerines in the Eastern and Western Palearctic differ in the number of feathers moulted. This difference is most likely the result of a large-scale climatic gradient in cold season duration and differences in time available for moulting. Eastern populations were characterized by a limited extent of feather moult that was additionally affected by migration distance and body mass. These results highlight the importance of linking annual cycle processes at the organismal level to the specific environmental conditions in the distribution range of each species.