Age-related differences in time budgets and parental care in wintering common cranes

Abstract

ABsTRcT.-We compared the behavior and food intake rate of parent, nonparent and juvenile wintering Common Cranes (Grus grus) to evaluate possible costs and benefits resulting from parental care. Time devoted to feeding and food intake rates were highest in autumn after arrival from the breeding areas, and decreased throughout the winter in all birds. This decrease was in part determined by a decrease in food availability, but also by satiation, as suggested by the increasing time devoted to resting and other nonforaging activities. Juveniles spent more time feeding and less time alert and preening than birds of both adult classes until February, but had achieved the same time budget as nonparent adults in March, when most juveniles were already independent from their parents. Increased feeding time allowed juveniles to obtain the same daily food intake as nonparent adults during the winter. Juveniles did not change their time budget when the family was in a flock, but the net intake rate of juveniles decreased due to interference from other birds. Parents spent less time feeding and resting, and more time scanning than nonparents. Parental vigilance effort was higher in isolated families than in flocks. However, parents seemed not to suffer from parental care, since their net and absolute intake rates were higher than those of nonparent adults. Received 3 October 1991, accepted 14 June 1992.