Daily activity patterns of a near-threatened endemic wetland specialist, the Southern African vlei rat (Otomys auratus)

The genus Otomys exhibits diverse activity patterns in the field, making them ideal subjects for studying circadian biology. The Southern African vlei rat (Otomys auratus) has previously been categorised as diurnal or crepuscular, but also displays some nocturnal activity. This study aimed to confirm the temporal niche of vlei rats in a laboratory setting and examine changes in activity when provided with a running wheel. The length of the free-running period was also calculated. In this study, 75 % of vlei rats displayed nocturnal activity rhythms when housed without a wheel. Access to a running wheel reduced individual variation and led to an increase in overall activity counts. All individuals had free running rhythms in constant darkness, with a period shorter than 24 h, which is consistent with other nocturnal rodents. This demonstrates that vlei rats are more active in darker conditions, likely as a means of avoiding diurnal avian predators in wetland habitats. With this species at risk of local extinction, this study is an important first step in understanding the behaviour of vlei rats under controlled conditions. As this species is displaced when its habitat becomes disturbed it may act as a useful bioindicator of wetland health and disturbance level.