Evol Ecol Res 5: 781-786 (2003)     Full PDF if your library subscribes.

The impact of thermoregulatory costs on foraging behaviour: a test with American Crows (Corvus brachyrhynchos) and eastern grey squirrels (Sciurus carolinensis)

A. Marm Kilpatrick*

Department of Zoology, University of Wisconsin, Madison, 1117 W. Johnson Street, Madison, WI 53706, USA

e-mail: kilpatrick@conservationmedicine.org


I attempted to test for the effects of thermoregulatory costs on the foraging behaviour of eastern grey squirrels (Sciurus carolinensis) and American Crows (Corvus brachyrhynchos). I examined the foraging of these two animals in paired trays filled with sand and sunflower seeds under cold winter conditions. One tray was exposed to direct solar radiation that reduced the thermoregulatory costs of the animal foraging in that tray. Both crows and squirrels foraged more in trays exposed to the sun, resulting in reduced giving-up densities (the mass of seeds remaining) in those trays. I also examined the foraging behaviour of American Crows under warmer conditions within their thermal-neutral-zone, and found no significant difference in giving-up densities between trays in the sun and the shade. This verified that the differences in giving-up densities (sun vs shade) found in cold conditions were a result of thermoregulatory costs and not something else (e.g. predation risk due to differences in lighting). As a result, this study provides the first direct evidence that thermoregulatory costs can play a significant role in the patch-leaving decisions of foragers. Solar radiation and temperature can cause differences in thermoregulatory costs and lead to changes in foraging pressure that may have important consequences for the distribution of seeds and other prey items.

Keywords: foraging costs, giving-up density, temperature.

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