Biometrics and sex ratios of skylarks alauda arvensis in winter in South-East Scotland

Abstract

Biometric data (wing length, tail length, head + bill, maximum tarsus) were collected from 255 individual Skylarks in winter at Musselburgh on the Lothian coast. Winglength and head+bill were measured most consistently by a single operator in the field. Winglength and tail length measurements were polymodally distributed, which allowed most birds to be allocated a sex class. Variation in the pattern of streaking of the under-tail coverts was noted, and is thought to represent individuality in plumage, although there may be an age-related bias in UTC streaking in males, which would repay further investigation. There were no significant differences from unity in the ratios of males to females caught in each of three winters with ‘normal’ weather, but in the one winter of severe weather, significantly more females than males were caught. From this ‘cold’ winter, there were significantly more retraps in later zuinters of birds caught during normal winter weather than of birds caught during severe weather. The only distant movements (three) reported were from the cold winter. Skylarks at Musselburgh appear to be rather site-faithful between winters. Results of the study are compared to those few from elsewhere, and it may be that nomadic flocks of Skylarks in winter, especially during spells of severe weather, are comprised largely of females, which are probably immatures. © 1997 British Trust for Ornithology.