A network-based analysis of signal use during approach interactions across sexes in chacma baboons (Papio ursinus griseipes)

Greetings in primates fulfil important functions including navigation of rank, maintenance of social relationships, and potentially establishing coalition partnerships. Papio makes a particularly valuable study genus as baboons show variation in greeting, male-male cooperation, philopatry, and social system. However, baboon greeting research has largely focused on male-male interactions, with female approach behaviour neglected except in relation to friendships and grunting. Most if not all signals seen in male-male greetings are also present in approaches between other sex combinations. To understand these signals further, their use in all sex combinations should be explored. We investigated approaches between male and female adult chacma baboons (Papio ursinus griseipes), the only savannah baboon reportedly lacking male-male cooperation, recorded in Gorongosa National Park, Mozambique. We compared male-male greetings with those of other baboon species, identified network clusters of co-occurring signals, and compared male and female approaches more broadly. Male-male approaches were similar to those in other baboon species. We identified several predictable signal combinations, ear-flattening with lip-smacking being a particularly strong signal of benign intent across sexes. Further research comparing greeting across sex combinations and species will help disentangle links between risk, cooperation, and greeting behaviour.