Brood-patch development and female body mass in passerines

Abstract

The brood patch in passerine birds is an area of thickened and vascularised skin which develops to facilitate incubation. In the British Trust for Ornithology Ringing Scheme, the stage of brood-patch development is recorded using a six-point scale. Since eggs represent a substantial proportion of adult body mass, the body mass of females may vary as a result of ovarian growth, egg laying and incubation. The aim of this study was to test the hypothesis that the body mass of females varies in relation to brood-patch stage, using ringing data collected at a single site in the UK during the breeding season. The data analysed were for females of four species of summer migrants and six resident species. Data for a migrant species in which the males also incubate and develop brood patches were also analysed to compare males and females at equivalent stages. In eight of the 10 species studied, female body mass was highest at a brood-patch score equivalent to a pre-incubation stage. There was a clear seasonal decline in female body mass for birds with fully developed or regressing brood patches. Comparisons of standardised body mass between species suggests that brood-patch data could be used to measure annual and regional variation in breeding phenology. © 2010 Taylor & Francis Group, LLC.