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Function of colored bill tips, stripes and spots in breeding gulls

Ferns, Peter Norman and Ross-Smith, Viola 2009. Function of colored bill tips, stripes and spots in breeding gulls. Marine Ornithology 37 (1) , pp. 85-92.

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We used independent contrasts analysis to investigate the function of differently colored tips, spots and stripes on the beaks of adult gulls. We combined continuous and categorical variables set out in an Open Document Format spreadsheet (available as Appendix 1 at the Marine Ornithology website) that can be adapted for similar analyses in other contexts. Our results show that a uniformly colored bill occurs in species with a small adult body size and a relatively large egg size (average egg length » 14% of body length), whereas a red gonys spot occurs in those with a large body size and a relatively small egg size (average egg length » 12% of body length). Both a differently colored bill tip and a black stripe on the bill occur in species with adult body and egg lengths of intermediate size (average egg length » 13% of body length). Egg length also increases more quickly per unit increase in body length in species of intermediate size than in the other groups. Patterned beaks may thus have evolved to focus the pecking response of chicks which are relatively small at hatching in relation to their parents, red spots being present in cases where the size difference is greatest. Such adaptations would have enabled adult gulls to evolve larger body sizes, without their eggs and chicks having to increase in size to the same extent.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Biosciences
Subjects: Q Science > Q Science (General)
Uncontrolled Keywords: gulls, beak colouration, body size, egg size, comparative analysis, independent contrasts
Publisher: Pacific Seabird Group
ISSN: 1018-3337
Last Modified: 04 Jun 2017 03:50

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