Direct observation of dispersal
In September 2018, we witnessed the dispersal of a subadult male, the oldest offspring of Group 1, from its natal home range and the formation of a new pair. First, we heard a single individual, presumably the subadult male, calling from the south-west border of Group 1’s home range, while the rest of the group was calling from the central part of its home range. The next day, we encountered the male in the company of an unknown female; they settled in an unoccupied area between the home ranges of Group 1 and Group 6 (Fig. 1). Until December 2018, this newly formed pair (Group 11) was having inter-group encounters with Group 1 almost every day, with calling and chasing between the pairs but no physical contact. As of September 2019, Group 11 was still occupying the same home range and had an infant born in February 2019. The female did not have any first-degree kin among the sampled animals, and her closest relative was the adult male of Group 4 with r = 0.156 (corresponding to a relatedness level between unrelated and half-sibling), with whom she also shared the same mtDNA haplotype (B; Supplementary Table 1).