The activ ity rhythm for the spinous country rat (Niviventer coxingi) was investigated based on 246 photographs taken by automatic camera systems from February 1992 to October 1993. Results show that the rats are a strictly nocturnal species, and probably also exhibit two- to th ree-hour ultradian cycles within their active period. Initiation of activity at dusk correlates closely with sunset, while the complete cessation of activity at dawn correlates with sunrise. Evidence suggests , however, that certain unidentified internal physio logical factors probably also are involved in the decreasing activity level before dawn. The rats stay active longer in autumn and winter than in spring and summer. T)1e higher activity level of the species during autumn and winter, as indicated by the number of photos being taken per unit of time, could have been caused by the need for more food or, also possibly, by higher population size during this period of time.
Rats, Nocturnal activity pattern, Seasonality, Automatic camera
