Activity Rhythms in the Marsupials Isoodon macrourus and Perameles nasuta in Captivity

Exercise wheels and closed-circuit television were used to record the activity rhythms of 34 1. macrourus and 32 P, nasuta (1) outdoors; (2) indoors with natural light; (3) indoors with artificial light in which the phases of night and day were normal; (4) same as (3) but with the phases of night and day reversed; (5) continuous dark; (6) continuous light. In tests (3)-(6) a faint red light was on continuously. These tests were made on animals caged singly or in pairs and lasted for periods of from 8 to 357 days. When a male and a female of different body weights were tested together, the animal using the wheel was identified by its weight. Five I. macrourus and 23 P. nasuta exposed to normal phases of night and day were active mainly during the dark periods. The daily activity pattern varied considerably but was fairly constant for individuals. When the phases of night and day were reversed, the animals continued to be active during the dark periods and, in many of them, the pattern of activity was similar to that under normal phases of night and day. They were, therefore, entrained to the artificial lighting system. However, in 17 out of 31 P. nasuta and 5 out of 31 1. macrourus exposed to reversed lighting conditions, activity started later each day. When the trigger for exercise began to fall close to the beginning of a light period, no activity was taken; the animals did not run in the wheel or take other exercise for 2-5 days, feeding and drinking were greatly reduced and some animals did not leave the nest box for 1-2 days. After this pause, exercise began again at the beginning of a dark period. In 10 I. macrourus exposed to continuous dark the period of the endogenous rhythm was either more than or less than 24 h, and in continuous light (four animals), the wheel-running activity was greatly reduced.