Thermal Consequences of Roost-site Selection: The Relative Importance of Three Modes of Heat Conservation

Thermal factors potentially important in the selection of nocturnal roosts by birds include shelter from wind, local increases in air temperature, and improvement in radiation balance. I analyze the relative importance of these three factors using data describing the thermal relations of Phainopepla nitens and the meteorological properties of winter roost sites selected by this species. Shelter from forced convection provides approximately 5 times more thermal benefit than improvement of radiation balance. Possible metabolic heating by the bird of air within the roost site is unimportant.