The temporal organisation of the feeding behaviour of four species of wallaby: examining chronobiological and homeostatic influences

Abstract

We studied the temporal distribution of feeding events of tammar wallabies, parma wallabies, brush-tailed rock-wallabies and swamp wallabies by infrared video-recording of captive animals maintained in a 12 : 12 light : dark cycle with constant temperature, and by radio-microphone surveillance of free-ranging animals on Kawau Island, New Zealand. Analyses of mean time spent feeding per 20-min period for tammar and parma wallabies showed significant circadian variation in both captive and free-ranging animals but not in captive or free-ranging brush-tailed rock wallabies or swamp wallabies. While there was no significant difference in the extent of circadian variation of feeding rate between tammar and parma wallabies there were significant differences according to the type of food being fed. Thus, circadian variation in feeding rate was greater in both species when standing sward was fed. None of the survivorship curves of the interfeed intervals of either captive or free-ranging animals showed a discontinuity suggestive of organisation of feed events into meals. There were bicrepuscular peaks of feed-event density in both captive and free-ranging tammar and parma wallabies. There was a similar bicrepuscular distribution of feed-event density in free-ranging brush-tailed rock-wallabies but a more uniform temporal distribution of this parameter in captive specimens. There was a more uniform circadian distribution of feed-event density in a single captive and a single free-ranging swamp wallaby. Thus the circadian incidence of the feeding events of tammar and parma wallabies were more resistant to changes in the incidence of stochastic environmental variables such as predation whereas those of bush-tailed rock-wallabies and swamp wallabies were more susceptible to changes in these stimuli.