We measured oxygen consumption rates of 8 Screech? Owls (4 red and 4 gray phase) at 4 environmental temperatures, -10?, -5?, 5?, and 15?C. These data demonstrated a significant difference in oxygen uptake between color phases at -10? and -5?C. This supports our hypothesis that red phase Screech Owls are restricted in their northern distribution by color-related metabolic differences from the gray phase birds. The problems of low red phase occurrence in the Gulf Coast states and their absence from the Western states remain to be studied.
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Thermal adaptiveness of plumage color in screech owls