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Energy Conservation and the Evolution of Flightlessness in Birds

Brian K. McNab
The American Naturalist
Vol. 144, No. 4 (Oct., 1994), pp. 628-642
Stable URL: http://www.jstor.org/stable/2462941
Page Count: 15
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Energy Conservation and the Evolution of Flightlessness in Birds
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Abstract

I examine the hypothesis that energy conservation contributes to the evolution of a flightless condition in birds by comparing the factors that correlate with basal rate of metabolism in kiwis and flighted and flightless rails and ducks. Flightless rails have low basal rates, the level of which decreases with pectoral muscle mass. Kiwis also have low basal rates and small pectoral masses. The small pectoral masses found in flightless grebes, the flightless cormorant, and the flightless parrot suggest that these species have low basal rates. Penguins and flightless ducks, in contrast, have neither low basal rates nor small pectoral masses because these birds use their wings for locomotion. These data are compatible with the hypothesis that energy conservation contributes to the evolution of flightlessness in species in which pectoral muscle mass is reduced. On oceanic islands, rails have evolved a flightless condition repeatedly, usually in association with a small body size. Both adjustments reduce energy expenditure, which thereby facilitates the persistence of rails in environments with limited resources. The evolution of flightlessness in insects may also be a response to a restricted resource availability, especially in persistent habitats characterized by low rates of production.

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