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How the longspur won its spurs: a study of claw and toe length in ground-dwelling passerine birds

Authors


  • Editor: Andrew Kitchener

Correspondence
M. de L. Brooke, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK. Tel: +44 1223 336610; Fax: +44 1223 336676
Email: m.brooke@zoo.cam.ac.uk

Abstract

Noting that some ground-dwelling passerine birds have remarkably long claws, reflected in such names as longclaw (Motacillidae) and longspur (Emberizidae), this comparative study assessed whether these features might aid movement over grassy ground vegetation. Using measurements of museum specimens, we found that, corrected for body size, larks (Alaudidae) living in grassy habitats (n=31) had significantly longer toes and claws and hence larger footspans than species dwelling on bare substrates (n=25). Using phylogenetically corrected contrasts, the claw result remained strongly significant, and the footspan result marginally significant, while there was no significant difference between the toes of the two groups. Among 15 matched pairs of other ground-dwelling passerines, where one member of the pair inhabits vegetated ground and the other inhabits bare ground, the former had significantly longer toes and claws and hence larger footspans. We conclude that ground-dwelling passerines living on vegetated, typically grassy ground, have larger feet, due to both longer toes and claws. This probably facilitates movement over uneven and unstable vegetation.

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