Time available for moulting shapes inter- and intra-specific variability in post-juvenile moult extent in wheatears (genus Oenanthe)

Abstract

Moult is a vital and endogenously controlled process in the avian life. However, birds may modulate their feather renovation properties, such as the extent of moult, based on exogenous factors. Despite the large body of knowledge about moult patterns, numerous questions remain unclear. In this study, we aimed to improve our knowledge about the factors that affect variation in the extent of the post-juvenile moult in passerines by performing inter- and intra-specific comparative analyses. We assessed the effect of internal and external factors on passerines’ moult by comparing post-juvenile moult extent among 16 wheatear species (genus Oenanthe) from the Palearctic Ecozone. The tested factors included migration distance used as a proxy of time available for moulting and habitat type. We also explored the relationship between the extent of the moult, migration distance, and sex in the Northern Wheatear Oenanthe oenanthe across a latitudinal gradient in Western Europe. The results indicate that post-juvenile moult extent in wheatears was negatively related to migration distance, such that species with shorter migration distances moult extensively compared to long-distance migratory species. In contrast, the extent of post-juvenile moult in the Oenanthe genus was not related to preferred habitat type (arid or non-arid) of the species. Migration distance was also related to post-juvenile moult extent in the Northern Wheatear, with fewer renewed feathers in northern populations. However, the extent of the post-juvenile moult did not differ between sexes. Thus, our results support that time constraints affect moult extent in long-distance migratory species and populations.