Sharing sleeping sites disrupts sleep but catalyses social tolerance and coordination between groups.

Sleeping refuges-like other important, scarce and shareable resources-can serve as hotspots for animal interaction, shaping patterns of attraction and avoidance. Where sleeping sites are shared, individuals balance the opportunity for interaction with new social partners against their need for sleep. By expanding the network of connections within animal populations, such night-time social interactions may have important, yet largely unexplored, impacts on critical behavioural and ecological processes. Here, using GPS and tri-axial accelerometry to track the movements and sleeping patterns of wild olive baboon groups (), we show that sharing sleeping sites disrupts sleep but appears to catalyse social tolerance and coordinated movement between groups. Individual baboons experienced shorter and more fragmented sleep when groups shared a sleeping site. After sharing sleeping sites, however, otherwise independent groups showed a strong pattern of spatial attraction, moving cohesively for up to 3 days. Our findings highlight the influence of night-time social interactions on daytime social relationships and demonstrate how a population's reliance on, and need to share, limiting resources can drive the emergence of intergroup tolerance.