Social determinants of affiliation and cohesion in a population of feral horses.
Investigating affiliative behaviors (e.g. proximity, grooming, cooperative behaviors) is essential to understand group cohesion and stability in animal societies, as they may foster, or be fostered by long-term social bonds and ultimately determine an individual's lifetime reproductive success. Despite growing interest in affiliative behaviors across a wide range of mammalian taxa, little focus has been given to feral horse populations. In this study, we examined the influence of dyadic social factors (sex, rank difference, familiarity and genetic relatedness) on affiliative behaviors and group cohesion. We collected data on 16 feral horse groups in Northern Portugal who were subjected to both predation pressures and anthropogenic interference. A combination of all occurrence sampling methods and drone technology was used to record the horses' social behavior and spatial data. Same-sex dyads showed a preference to remain in close proximity, however they did not groom as frequently as different-sex dyads. Similar rank individuals were observed in proximity more often than non-similar rank individuals, but only in newly formed groups. Familiar individuals spent more time in proximity and groomed more often than unfamiliar (new) dyads. However, affiliation between conspecifics was not predicted by genetic relatedness. These results suggest that social bonds and group cohesion are mostly sustained by familiar individuals in both stable and newly formed groups. While maintaining close proximity may function to sustain bonds between same-sex individuals, grooming may reinforce both intra-sexual and inter-sexual bonds. Examining the variation of affiliation patterns on horse populations may shed light on their behavioral plasticity and have crucial implications for the welfare and conservation of horse breeds.