Evidence of helping behaviour in a free-ranging population of communally breeding warthogs

Cooperative breeding societies are defined by the presence of helpers. Defining helping behavior in cooperatively breeding mammals has been difficult because lactation limits the ability of individuals to pro- vision non-genetic young. As a consequence, ‘‘helping’’ behavior has frequently included predator and conspecific defense and thermoregulation. However, these behaviors are often associated with the benefits of group living and their expression may not warrant a species’ classification as a cooperative breeder (e.g., many ungulates and pinnipeds). In this study, we examine cooperative breeding behavior in the common warthog, Phacochoerus africanus. Warthogs exhibit substantial variation in breeding strategies and females will raise their young alone or in association with other females. The size of warthog groups varies throughout the year and we investigate fission and fusion of individual breeding groups to elucidate the costs and benefits of adopting different reproductive strategies. We found that the cohesion of female groups was related toparturition suggesting that there are benefits to sociality that are related to the production and care of offspring. Additionally, we found that reproductively-aged group members will help other group members by both baby- sitting and adopting the group’s offspring indicating active selection for cooperation. We did not witness any inci- dences of yearling group members exhibiting these behaviors indicating differential trade-offs to cooperation possibly related to the helper’s age/experience.