Sexual size dimorphism and sources of variation in the growth of wing feathers in nestling Pied Flycatchers Ficedula hypoleuca

I report a 5-year field study of the growth of flight feathers, as scored by the lengths of the wing and first-primary feather, of Pied Flycatcher nestlings when they were 13 days old. Further evidence to that already published for gender differences in growth of different traits (fledgling tarsus length, mass and body condition) being already present early in the ontogeny in a passerine species with slight adult size dimorphism is presented. Familial and environmental sources of resemblance in both feather traits are suggested by highly significant correlations of feather growth within siblings, and within individual nestboxes independently of the identity of parents breeding therein. Retrospective analyses of gender differences in feather growth at the nest for a sample of recruited young show that feather traits of female fledglings were, on average, larger than those of males. However, the difference is reversed at recruitment due to compensatory gains in males that may be related with positive directional selection on wing length in males related to an early settlement in spring in this long-distance migrant.

Potti, J., Ardeola 47(1), 2000, 37-47