Circadian Activity Rhythms of Captive Heath Rats (Pseudomys shortridgei)

Abstract

The activity rhythms of four male and four female heath rats (Pseudomys shortridgei) were monitored under natural lighting for 35 days. Activity was detected with passive infrared sensors and recorded on data loggers. Data down-loaded from the loggers were plotted as actograms on a line-printer. During the 35-day recording period, all heath rats showed a markedly nocturnal activity pattern, with 87·7% of activity occurring during the night. In all heath rats, activity levels increased markedly across the night. Activity was bimodally distributed, with the highest levels occurring just prior to dawn. However, a second smaller peak in activity occurred just after dusk. With increasing seasonal photoperiod, all heath rats showed a concomitant compression of nocturnal activity. Little difference was found between activity patterns of males and females. Male heath rats displayed 85·7% (s.d. 4·8%) of their activity at night while females showed 89·7% (s.d. 5·4%) of their activity at night. During the daylight hours, heath rats remained in their nest boxes and emerged on most days just prior to, or at, sunset. The pattern of activity observed in these captive heath rats appears to be more nocturnal than that of heath rats living under natural conditions. This difference may reflect the fact that, in captivity, food was available ad libitum and was of high quality. In the natural habitat, heath rats probably have to spend more time foraging, and food may be of poorer quality. The additional time spent foraging would extend activity into the daylight hours.