Sexual size dimorphism and moult in the Plain Swift Apus unicolor

• Published in: Ringing & migration Vol. 24; no. 2; pp. 81 - 87
• Main Authors: Garcia-Del-Rey, Eduardo, Gosler, Andrew G., Gonzalez, Javier, Wink, Michael
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 01.01.2008
• ISSN: 0307-8698; 2159-8355
• DOI: 10.1080/03078698.2008.9674379

The biometrics and moult of swifts are poorly known, yet represent important aspects of their breeding biology. In this study we investigated moult and used molecular sexing to characterise sexual size dimorphisms in the Plain Swift Apus unicolor. In contrast to previous work based on skin specimens, males were significantly larger than females with respect to wing length (2.0 mm difference) and tail length. The sexes did not differ in body mass. We derived a discriminant function by binary logistic regression to separate the sexes using wing, bill and tail length; the function was accurate in assigning 70% of the birds to their correct sex. Moult data obtained from 30 birds suggested that almost 25% of individuals overlapped breeding with the start of moult (estimate: 16 August ± 20 days) and that the progress of primary-feather moult was slow and initiated from at least two moult centres. Further studies are needed to investigate moult in relation to migratory strategy in this swift species.