Seasonal Changes in Body Weight and Composition of Australian Bush Rats, Rattus fuscipes, and Adaptation to Winter

Abstract

A montane population of Australian bush rats, Rattus fuscipes, was studied for 3 years. Bush rats were also kept in captivity in natural conditions of temperature and light during the same period; these rats had food and water ad libitum. The body weights of free-living rats declined in autumn, and those of captive rats in winter. Changes in organ weights and body composition fell into three groups. (1) Testes, heart, spleen and adrenals were lighter in winter than in summer. (2) Hair weight increased gradually from February to a peak in June. The weight of carcass lipid and of brown adipose tissue increased rapidly in late autumn (May). (3) Body weights, and the weights of the lean carcass and the liver, were at a minimum in May, had a minor peak in June, and declined again in July and August. There was no evidence that any of these changes were related to diet or to food supply.