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A comparative test of the correlated evolution of flightlessness and relative brain size in birds

Published online by Cambridge University Press:  18 June 2004

Andrew N. Iwaniuk
Affiliation:
Division of Birds, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013-7012, U.S.A. School of Biological Sciences, Monash University, Clayton, Victoria, 3168, Australia
John E. Nelson
Affiliation:
School of Biological Sciences, Monash University, Clayton, Victoria, 3168, Australia
Helen F. James
Affiliation:
Division of Birds, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013-7012, U.S.A.
Storrs L. Olson
Affiliation:
Division of Birds, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013-7012, U.S.A.
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Abstract

Secondary flightlessness has evolved independently many times in birds. Morphological changes in the pectoral girdle and flight feathers and changes in body size have been associated with the evolution of flightlessness, and it has also been suggested that flightless birds have relatively small brains. We therefore tested whether flightlessness is related to changes in relative brain size. Relative brain size was compared between volant and flightless species using both conventional statistics and modern comparative methods within nine taxonomic groups. No significant difference was found between flightless and volant species in six of these groups, regardless of whether body mass or tibiotarsal measurements were used as estimates of body size. Species with relatively smaller brains compared with their volant relatives were the great auk Pinguinus impennis, the kakapo Strigops habroptilus and some species of penguin. Thus, we found no evidence of a general correlation between the evolution of secondary flightlessness and the evolution of relatively small brains in birds. This suggests that neural requirements are not significantly different between flightless and volant species, although our methods may have overlooked subtle neurological changes that do not result in markedly different endocranial volumes.

Type
Research Article
Copyright
2004 The Zoological Society of London

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