Fitness and feather wear in the Collared Flycatcher Ficedula albicollis

Individual variation in the degree of feather wear is potentially a useful marker of individual quality or fitness, but next to nothing is known about causes and fitness consequences of feather wear in birds. We studied the effects of sex, age, year and experimental manipulation of blood size on primary feather wear in Collared Flycatchers Ficedula albicollis, and related variation in degree of feather wear to differences in fitness (viz. recruitment, survival). At the end of the breeding period, females and young birds had more worn flight feathers than males and adult birds, and the sexual difference in the degree of feather wear was particularly pronounced in one of the two study years. Experimental reduction of brood size reduced the degree of primary feather wear, whereas experimental enlargement of brood size did not lead to increased Feather wear. In both sexes, there was a clear tendency for very old ( > 5 years old) birds to have more worn feathers than middle aged birds. The individual differences in the degree of feather wear were not correlated with individual differences in recruitment rate of young, but survival probability to the nest breeding season increased with increasing degree of feather year.