Personality homophily drives female friendships in a feral ungulate

Friendships, exhibited by both humans and non-human animals, have considerable adaptive benefits. In humans, similarity or homophily in personality is considered a proximate mechanism driving friendships, yet little is known about the behavioural decision rules underlying animal friendships. Some empirical research suggests that animal friendships can be driven by personality homophily. However, these studies are restricted to non-human primates, limiting our understanding of the mechanisms of friendships. We investigated a feral population of water buffalo (Bubalus bubalis) to determine whether homophily in personality drives friendships in this non-model social species in free-ranging environmental conditions. We conducted observations on females (n=30) and assessed their friendships and personalities. Close spatial proximity served as a behavioural indicator of friendship, validated by affiliative body contact. An objective bottom-up method revealed three personality traits - social tension, vigilance, and general dominance. We found that females with comparatively lower personality differences in social tension and general dominance traits exhibited significantly higher close spatial associations. We did not find an effect of kinship on close spatial associations. Our findings show that friendships in buffalo can form based on personality homophily, a decision rule attributed predominantly to primates. We discuss these findings in light of buffalo socioecology but emphasise their implications in the broader evolutionary context of animal personalities and friendships.