The Effects of Insolation on the Diurnal Feeding Pattern of White‐Crowned Sparrows (Zonotrichia Leucophrys Gambelii)

Feeding activities of White—crowned Sparrows (Zonotrichia leucophrys gambelii) were observed in the field and recorded in captives held outdoors and indoors. To determine the importance of solar radiation in the daily energy budget the relationship of the diurnal feeding pattern to concurrent conditions of solar and artificially produced radiation were compared. A morning decrease in feeding activities of wild flocks begins before the air temperature starts to increase and coincides with sunrise. There is a more pronounced decrease in feeding on warm, clear days than on cold, cloudy days. The feeding pattern of captives held outdoors is modified during exposure to direct insolation. Food intake is inhibited while the birds are in sunshine. Birds held indoors and exposed to levels of short—wave infrared radiation that are submaximal in the field eat the same as control birds when air temperature is a constant 20°C. When the air temperature is held at 7°C, however, the irradiated birds eat significantly less than the control birds. These data are taken collectively to mean that sun—bathing has adaptive value because it alleviates the energy costs of thermoregulation when the birds are in cool conditions below their zone of thermal neutrality. The rapid adjustments of food intake during periods of insolation suggest that peripheral heat reception may be a source of information to the neural centers regulating appetite. The initiation of sunning hehavior is probably evoked by a variety of sensations.