Hibernation and circannual rhythms of food consumption in marmots and ground squirrels.

In order to understand better the evolution and adaptive value of hibernation, ecological aspects and experimental studies of closely related hibernators, the Marmotini, are examined. The central hypothesis is that annual changes in the environment integrate three or, perhaps, four physiological processes: torpor, reporduction, consumption of food, and metabolism. Reproduction occurs promptly after emergence from hibernation. For most species, the breeding season is very short. Although the experimental data are rather meager, no variation in external factors has consistently altered the season of reproduction. Consumption of food and change in weight increases until July or September and then decreases. The large members of the Marmotini store their energy as fat, but small species store their energy as seeds and nuts. Experiments to test the hypothesis that some aspect of the supply, such as fat content, might vary seasonally have produced negative results. Complex experiments on the length of the photoperiod on woodchucks and several species of ground squirrels failed to alter the annual cycle of consumption of food. Animals kept in constant conditions showed a cycle of about 11 months, but woodchucks sent tto Australia changed their cycle in two years to match the seasons of the southern hemisphere. Experiments with temperature and torpor and castration did not alter the annual did not alter the rhythm...