The biometrics of Twite Carduelis flavirostris in Ireland and Britain

In this paper we analyse and compare biometric data of Twite Carduelis flavirostris from Ireland, England and Scotland (Orkney). Data were separated by season (breeding or winter) to account for potential mingling of populations during the winter. The mean wing length of wintering male Twites, but not females, differed significantly between the countries. In the winter, for both sexes, Scottish Twites were significantly heavier than Irish and English ones, which did not differ from one another. Breeding Irish Twites were heavier than breeding English Twites, in both sexes. Males in all countries had longer wings than females. Males were heavier than females in Ireland and England but sexes were of equal mass in Scotland. These results raise questions about the structure, origins and behaviour of wintering Twite populations. Some of the difficulties of ageing and sexing Twites are discussed.