Abstract
Complex sociality in primates often is argued to have evolved after the appearance of diurnal activity. Studying the behaviour of nocturnal primates is fundamental to understanding the evolutionary origins of primate behaviour and ecology, yet much less is known about the nature of sociality in nocturnal primate species than their diurnal counterparts. We investigated group size, communication, and social interactions in free-ranging, Northern lesser galagos ( Galago senegalensis ) and present an activity budget and assessment of temporal variation in their behaviour. We collected continuous behavioural data using focal follows at three different stages of the night from individuals at Kwakuchinja, Northern Tanzania. We also collected group size data from Northern lesser galagos at Fongoli, Southeastern Senegal, and Lolldaiga Hills Ranch, Central Kenya. We categorised behaviours and, where sample sizes permitted, used Kruskal–Wallis tests to compare the durations of observed behaviours between the morning (pre-dawn), evening (from dusk), and later in the night. We analysed 140 focal follows (31.4 h of continuous behavioural data) and found that the proportion of time spent foraging, inactive, in locomotion, in self-maintenance, and vigilant, varied across the three stages of the night; galagos spent a great deal of their time inactive in the morning and foraging was more prevalent in the evening. Group size at Kwakuchinja was significantly larger than at Fongoli or LHR. Galagos were in groups of two or more in the majority of encounters at Kwakuchinja (55%; N = 76), rather than alone, but spent most of their nighttime activity alone at Fongoli (79%; N = 185) and LHR (80%; N = 142). Overall vocalisation rates were higher in the morning than other times throughout the night, although contact calls were relatively more frequent in the evening than other times. We recorded both affiliative and agonistic social interactions, but these contributed almost nothing to the overall activity budget. Our preliminary investigation into the social structure of Northern lesser galagos suggests that there are population differences in sociality and that overall, they connect more through vocalisations than through direct social interactions, thereby avoiding some of the potential costs associated with group-living. This variation in social organization suggests that we have more to learn about the drivers of sociality in nocturnal primates and the nature of their social structure.