Biometrics of the Twite Carduelis flavirostris

Publication Type:Journal Article
Year of Publication:2001
Authors:Clark, H, Sellers, RM
Journal:Ringing & Migration
Volume:20
Issue:4
Date Published:2001
ISBN Number:0307-8698
Keywords:Carduelis, Carduelis flavirostris, Fringillidae, Ireland, Linaria, Linaria flavirostris, United Kingdom
Abstract:This paper presents a summary of information on the biometrics of the Twite Carduelis flavirostris based on measurements of live birds captured during the winter months in Caithness, weights of birds caught on Fair Isle, North Ronaldsay, Spurn Point and Oronsay, and wing and tail lengths of skins of birds collected in Britain, Ireland and Scandinavia. A significant sexual dimorphism was found in wing and tail lengths, with males being the larger sex, but not in tarsus or bill length; no significant age?related differences were found. Scandinavian birds (C. f. flavirostris) had significantly longer wings and tails than British or Irish birds (C. f. pipilans). There was also significant variation in these two parameters within Britain & Ireland and a significant trend of both mean wing and tail length with latitude and longitude. It is concluded that there is a roughly southwest to north?east cline in body size within the western European population of the Twite. Birds wintering in Caithness increased weight progressively more or less throughout the hours of daylight at rates of 0.15g h?1 in females and 0.21 g h?1 in males. Weights also increased steadily from October to December, changes which were largely parallelled by increases in fat. Females reached their maximum weights during the breeding season whilst males reached a maximum around the beginning of moult in July. Lowest weights occurred in late winter and around the end of moult. The weights of birds caught on migration were similar to those of birds trapped in mid?winter and it is estimated that such birds maintained around 1g fat, sufficient to enable the birds to fly c. 300km in still air, which is at the upper end of the range of distances Twites typically move in Britain.This paper presents a summary of information on the biometrics of the Twite Carduelis flavirostris based on measurements of live birds captured during the winter months in Caithness, weights of birds caught on Fair Isle, North Ronaldsay, Spurn Point and Oronsay, and wing and tail lengths of skins of birds collected in Britain, Ireland and Scandinavia. A significant sexual dimorphism was found in wing and tail lengths, with males being the larger sex, but not in tarsus or bill length; no significant age?related differences were found. Scandinavian birds (C. f. flavirostris) had significantly longer wings and tails than British or Irish birds (C. f. pipilans). There was also significant variation in these two parameters within Britain & Ireland and a significant trend of both mean wing and tail length with latitude and longitude. It is concluded that there is a roughly southwest to north?east cline in body size within the western European population of the Twite. Birds wintering in Caithness increased weight progressively more or less throughout the hours of daylight at rates of 0.15g h?1 in females and 0.21 g h?1 in males. Weights also increased steadily from October to December, changes which were largely parallelled by increases in fat. Females reached their maximum weights during the breeding season whilst males reached a maximum around the beginning of moult in July. Lowest weights occurred in late winter and around the end of moult. The weights of birds caught on migration were similar to those of birds trapped in mid?winter and it is estimated that such birds maintained around 1g fat, sufficient to enable the birds to fly c. 300km in still air, which is at the upper end of the range of distances Twites typically move in Britain.
URL:http://dx.doi.org/10.1080/03078698.2001.9674259
Short Title:Ringing & Migration
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