Group Size Effects in Quokkas

The amount of time allocated to vigilance, foraging, and locomotion as a function of group size were studied in the quokka (Setonix brachyurus), a small, moderately social, macropodid marsupial, on Rottnest Island. Despite living in isolation from most predators for up to 7000 years, quokkas exhibited typical group size effects of aggregation: they foraged more and showed less visual vigilance as group size increased. Group size effects, therefore, may result from factors other than antipredator benefits. In groups larger than 10, quokkas, uniquely among macropodids, allocated virtually all of their time to foraging and none to looking. Given virtually no predation risk on Rottnest Island and no antipredator benefit from aggregation, competition for food or other resources may also be important factors influencing time allocation in quokkas. Quokkas seemingly retained some apparent antipredator behaviour: they remained sensitive to the distance they were from cover and to the time of day when allocating time to foraging and looking.