Abstract
The two groups of mammals whose activity patterns have been most intensively studied are the rodents and the insectivores. All rodents investigated so far have a 24-h rhythm which is regulated by light. It is most marked in nocturnal rodents like species of Apodemus, Peromyscus and Rattus, less distinct in Mus and least marked in Microtus, which is almost as active by day as by night (references in Southern 1954). Among the insectivores, a 24-h rhythm is present in Sorex spp. (Crowcroft 1954; Ingles 1960), but is not apparent in Talpa (Godfrey 1955). All of these have also a short-term or feeding rhythm, with a periodicity related to body size, i.e. 1-1I h in Sorex minutus, 1-1k h in Mus, 2j h in Microtus, 4 h in Rattus and 8 h in Talpa. Almost nothing is known about the activity rhythms of marsupials. Gurwell (1959) recorded the activity of a single male opossum (Didelphis) under different lighting conditions. Hickman & Hickman (1960) observed pigmy possums (Cercaertus, Eudromicia) daily for over 12 months. Caughley (1964) carried out a field study of activity in the red kangaroo (Megaleia rufa Desmarest) and the grey kangaroo (Macropus canguru Muller). In a study of wheel-running behaviour, Packer (1966) found a 24-h (circadian) rhythm in the Tasmanian devil (Sarcophilus). The principal methods used in laboratory studies of activity are reviewed by Reed (1947) and Southern (1964). Measuring devices include the running wheel, tambourmounted cage, treadle and photoelectric cell (see Veenstra 1958), each connected to a recording instrument such as a post-office meter or revolving drum. In such studies, the kind of activity studied depends upon the apparatus used: thus the running wheel generally measures running activity alone, while the tambour-mounted cage registers other movements as well. Recent studies have attempted to record total activity (Clarke & Hawkins 1957; Kavanau 1962; Chambers & Salmons 1966), and the apparatus used by Kavanau is, in fact, able to record and simultaneously to analyse the separate components of activity.
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