Tammar wallabies (Macropus eugenii) associate safety with higher levels of nocturnal illumination

Moonlight is commonly reported to increase the time nocturnal animals allocate to antipredator vigilance and to affect space use patterns because predation risk increases as a function of light intensity. The majority of studies reporting moon-light effects have been conducted on small-body sized mammals which are relatively vulnerable to a variety of predators. Moonlight effects were studied experimentally on a mid-sized mammal, the tammar wallaby (Macropus eugenii), a macropodid marsupial. Four groups of six adult female wallabies were observed for 6 days during each of three moon phases (no moon, quarter moon and full moon). In addition to natural illumination, wallabies were exposed to 2 days each of three artificial light treatments (no light, red light, white light) during each moon phase treatment. Subjects were videotaped at night with an image intensifier affixed to a video camera. Time budgets were calculated from the video record, and later analyzed in a repeated-measures factorial ANOVA. There was no effect of natural moonlight on time allocation, suggesting that wallabies had no endogenous cycle associated with moonlight. There were effects of artificial illumination and of the experimental group on time allocation. Wallabies tended to forage more and allocate less time to antipredator vigilance under the two light treatments, suggesting that, unlike previous studies on a variety of other taxa, they associated safety with increased illumination. We speculate that differences among groups might reflect the different seasons over which wallabies were studied. Results suggest that the nocturnally active tammar wallaby exercises caution in the dark.