Sexing, ageing and moult of Buzzards Buteo buteo in a southern European area

In order to obtain a reliable method for sexing and ageing Buzzards Buteo buteo breeding in southern Europe, 115 birds from a wildlife rehabilitation centre and 43 trapped birds were measured, sexed and aged over four years (2000–2003). Dead birds were sexed by examining their gonads, and live birds by the presence of a brood patch. Wing length, minimum tarsus width and body weight were the only variables which differed significantly between the sexes, although there was much overlap for the wing length and weight. Buzzards with less than 7 mm minimum tarsus width were male and those greater than 7.9 mm were female. Birds did not complete moult in one year, moulting less than 60% of the flight feathers in one season. The first and the second moult followed a pattern, but afterwards moult was unpredictable and totally asymmetric. Also, half the females and 33% of males had started to moult within 30 days of their chicks hatching. These results differ from those published for Buzzards from northern Europe. The size and moult pattern depend on factors such as prey availability and migratory status, which in turn vary between areas. We therefore suggest caution when considering the moult strategies, ageing criteria and sexing criteria published for other countries.