Redefining the activity pattern of the honey possum (Tarsipes rostratus).

Abstract

ANIMALS are commonly separated into two major categories based on their activity patterns: diurnal and nocturnal. However, evidence of numerous species exhibiting diverse periods of activity, including arhythmic and crepuscular habits, broadens the description. The honey possum (Tarsipes rostratus), a small West-Australian marsupial feeding exclusively on nectar and pollen, has been described as strongly nocturnal (Wooller et al. 1981; Russell and Renfree 1989). However, infrequent daytime activity in captivity (Russell 1986) and in the wild under cold, cloudy conditions, has been reported (Hopper and Burbidge 1982; du Plessis and du Plessis 1995). During trapping exercises in the region of Jurien Bay (250 km north of Perth, Western Australia), several animals were observed foraging after sunrise and before sunset, with occasional diurnal activity. To date, no study has investigated directly the activity periods of the species. Furthermore, studies of the visual capabilities of T. rostratus revealed that its retinal organisation is not compatible with a nocturnal lifestyle, but presents features comparable to those found in diurnal species (Arrese 2002; Arrese et al. 2002). Such discrepancies warranted the monitoring of activity periods (rhythmicity) of T. rostratus in its natural environment, a study reported here. We discuss our results in the context of the visual ecology of the species.