Diurnal Feeding Patterns in White-Crowned Sparrows, Zonotrichia leucophrys gambelii

Abstract

Food intake was measured continuously in the laboratory with a strain-gage apparatus and in the field by direct observation. Feeding patterns were related to the possible effects of daily and seasonal changes in the environment and in physiological state, and to the characteristics of premigratory and intramigratory fattening. The thermal environment has important effects on the daily total and pattern of caloric intake. The total daily intake of caged birds outdoors is inversely correlated with the mean daily air temperature both before and during premigratory hyperphagia but the diurnal pattern of intake is usually not affected by the daily cycle in air temperature. During premigratory hyperphagia wild flocks feed more intently than usual during midday. This alteration in feeding pattern probably indicates the origin of the extra energy that is accumulated as fat stores. Both wild and captive birds stop eating in the evening earlier than usual once they have accumulated maximum lipid reserves. It is suggested that this advance in the termination of feeding in birds showing a physiological readiness to migrate involves a negative feedback of lipid reserves on appetite, and that the early termination of feeding is adaptive because it provides a time interval for emptying the digestive tract just prior to migratory flight.