Sleeping Site Selection in the Nocturnal Northern Lesser Galago ( Galago senegalensis ) Supports Antipredator and Thermoregulatory Hypotheses

Sleep is an important and time-consuming activity, during which animals may be particularly vulnerable. Selecting a suitable sleeping site is therefore essential for an individual’s fitness. Here we test the importance of antipredator and thermoregulatory hypotheses for the sleeping site preference of a nocturnal primate, the Northern lesser galago ( Galago senegalensis ), in Northern Tanzania. During June to August of 2015 and 2016 we conducted daily surveys of sleeping sites to record the number of galagos and their location within the sleeping tree, and used focal follows to record when galagos reached and left sleeping sites. We collected vegetation data for sleeping sites ( N = 47) and matched controls, and placed data loggers in sleeping ( N = 14) and control locations to compare temperature and humidity. Sleeping group sizes were similar to that of G. senegalensis in The Gambia, and the mean proportion of visits in which galagos were present at each site was 27 ± SD 25%. Galagos slept on branches ( N = 29), nests ( N = 6), palm leaves ( N = 6), and in tree cavities ( N = 1). Palm leaves have not been previously recorded as regular sleeping sites for galagos and were overrepresented relative to their occurrence in the habitat. Random forest classification analysis revealed that galagos sleep in areas with greater canopy cover and connectivity, greater mid-level vegetation cover, higher tree density, and a greater number of Acacia trees. Sleeping locations had significantly lower mean temperatures but greater mean humidity than control locations. Our findings support predator avoidance and thermoregulation as drivers of nesting behavior. In particular, the characteristics of galago sleeping sites correspond well to those expected for protection from aerial predators, while those related to protection from terrestrial predators seem to play a minor role.