Grouping patterns in warthogs, Phacochoerus africanus: is communal care of young enough to explain sociality?

Group-living will evolve when individuals increase their lifetime reproductive success by joining with other individuals. In cooperatively breeding societies, individuals living in a group will participate in the communal rearing of young. Several factors can influence the evolutionary trade-offs of grouping and it is often unclear whether cooperative breeding is advantageous or is simply a by-product of selection acting on grouping behaviour. We used sightings of 1318 warthogs in 711 groups to investigate whether the advantages of sociality in the warthog differ depending on an individual's age, sex, reproductive state, or the time of year. Adult males only formed temporary associations with other individuals indicating that participation in a group was not advantageous. In contrast, yearlings were almost inevitably found in groups, regardless of their sex or time of year, suggesting any costs to sociality were outweighed by the benefits. Grouping in adult female warthogs was complex; adult females were more likely to form groups in the presence of juveniles and when juveniles were at their most vulnerable stage indicating that sociality in females could be partially explained by the benefits of communal care of young. However, other factors influenced female cooperation including group composition and the time of year.