Young individuals of many passerines undergo a partial moult and replace most of their body feathers and a variable number of coverts and minor wing feathers. In many species, this moult generates perceptible coloration differences, which may act as status signals. This study analyses how the extent of partial moult is related to different estimators of condition. A total of 43 young White Wagtails Motacilla alba caught in an urban roost in the city of Seville were analysed. The extent of their partial moult was positively correlated to the heterophil-lymphocyte ratio, but not to the abundance of leukocytes or to body mass. Individuals with more adult-like plumage may be exposed to higher stress due to the aggressiveness of territorial adults. Consequently, the increased heterophil-lymphocyte ratio found in the study is probably a consequence of the extent of moult rather than an explanation of intraspecific variation in the extent of moult.

Peer reviewed