The extent of white plumage patches in female Pied Flycatchers Ficedula hypoleuca is negatively associated with corticosterone concentration in partly unpigmented feathers

Abstract

Sexually and socially selected signals are predicated to express the present and past condition of individuals and thereby their capacity to cope with environmental challenges. The concentration of corticosterone in feathers (CORTf) has been validated as a marker of activation of the hypothalamic-pituitary axis in birds during feather development. Measurements of CORTf can thus express the physiological stress of migratory birds during non-breeding periods of the annual cycle when feathers moulted in the wintering range are analysed. Thus, negative trends of ornament expression with CORTf may be predicted. Unpigmented plumage patches may constitute signals of phenotypic quality and are used in many species in social interactions by both sexes. Pied Flycatchers of both sexes Ficedula hypoleuca show white forehead and wing patches during the breeding season, of which the forehead and part of the wing patch (tertials) are moulted on the wintering grounds before spring migration. These patches are used as signals in social and sexual interactions and their expression has been previously related to several indicators of physiological status. We collected tertials of females during nestling provisioning in a Spanish population and determined their CORTf in the laboratory. CORTf was thus measured in some of the prenuptially moulted feathers used as signals of social dominance by breeding females. According to AICc model selection, CORTf turned up in all the best models explaining forehead patch size and in most best models for wing patch size when controlling for age and size. Both forehead and wing patch sizes were negatively related to CORTf, although the trend for wing patch size was not significant. This indicates that breeding females expressing large unpigmented patches experienced low levels of stress during the prenuptial moult in their winter quarters, or that strongly signalling individuals present a lower level of activation of the HPA axis.