Campus Units

Ecology, Evolution and Organismal Biology

Document Type

Article

Publication Version

Published Version

Publication Date

7-2010

Journal or Book Title

Auk

Volume

127

Issue

3

First Page

626

Last Page

635

DOI

10.1525/auk.2010.09213

Abstract

Sexual size dimorphism occurs throughout the animal kingdom, and its ecological and evolutionary causes and implications have been intensively studied. Sex-specific differences in bill curvature are known in several species of birds, including some tropical hummingbirds. Despite the importance of bill shape for foraging, comparative studies of sexual dimorphism of bill shape are few. We quantified bill shape in two temperate hummingbird species, Black-chinned Hummingbird (Archilocus alexandri) and Ruby-throated Hummingbird (A. colubris) and compared patterns of sexual shape dimorphism. Several commonly used bill-curvature indices yielded contrasting results; one found differences between species and sexes, a second identified no differences in curvature, and a circle-curvature approach revealed shape differences between species and between the sexes. By contrast, landmark-based geometric morphometric methods identified significant differences in sexual shape dimorphism and also revealed that Ruby-throated Hummingbirds exhibited significant sexual differences in shape, whereas Black-chinned Hummingbirds did not. Female Ruby-throated Hummingbirds exhibited relatively greater bill curvature than males, a pattern consistent with observations of some tropical hummingbirds. Although the causes of differences in bill-shape dimorphism between Black-chinned and Ruby-throated hummingbirds remain unclear, we hypothesize that it may be attributable to differences in the structure of the community in which each species breeds and the interplay between inter- and intraspecific competition for resources in these communities. Finally, we recommend that future studies of bill shape include geometric morphometric approaches because they are better suited than univariate approaches for identifying more complex shape differences within and among species.

Comments

This article is from the Auk 127 (2010): 626, doi:10.1525/auk.2010.09213. Posted with permission.

Copyright Owner

American Ornithologists' Union

Language

en

File Format

application/pdf

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