Ageing and sexing of snow buntings wintering on the Aberdeenshire coast, their biometrics and sex ratio

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Abstract
We describe a method of ageing and sexing Snow Buntings in winter using the colour of wing feathers. Adults were best distinguished from first winter birds using feather wear. On average, males had longer wings than females but there was no difference in the average wing lengths of the age groups. On the basis of plumage colour, the sex ratio of the population in 1986/87 was about four females to every male. Using the frequency distribution of wing lengths, the sex ratio in 1985/86 was similarly biased but in the two previous winters the ratio was approximately even. We suggest the excess of females could be explained if they came from Iceland or Norway, where most males could winter locally. Male Snow Buntings may generally winter further north than females. We speculate that more males migrate south in severe winters when food is less available in the north.