Data for: Weak, but not strong, ties support coalition formation among wild female chimpanzees

In social species, individuals may be able to overcome competitive constraints on cooperation by leveraging relationships with familiar, tolerant partners. While strong social ties have been linked to cooperation in several social mammals, it is unclear the extent to which weak social ties can support cooperation, particularly among non-kin. We tested the hypothesis that weakly affiliative social relationships support cooperative coalition formation using 10 years of behavioural data on wild female chimpanzees. Female chimpanzees typically disperse and reside with non-kin as adults. Their social relationships are differentiated but often relatively weak, with few dyads sharing strong bonds. Females occasionally form aggressive coalitions together. Three measures of relationship quality - party association, five-meter proximity, and whether a dyad groomed - positively predicted coalitions, indicating that relationship quality influenced coalition partnerships. However, dyads that groomed frequently did not form more coalitions than dyads that groomed occasionally, and kin did not cooperate more than expected given their relationship quality. Thus, strong bonds and kinship did not bolster cooperation. We conclude that cooperative coalitions among female chimpanzees depend on social tolerance but do not require strong bonds. Our findings highlight social tolerance as a distinct pathway through which females can cultivate cooperative relationships.

Methods
This data is comprised of behavioral data on adult female chimpanzees living in Kibale National Park from 2010-2019. For analysis 1 (long term correlational analysis), behavioural observations are summarized into dyadic rates and counts of behaviors per two year time periods. This includes the number of times the dyad was in the same party, the number of coalitions the dyad engaged in together, a five-meter association index, a grooming duration index, whethere or not the dyad ever groomed dudring the period (0/1) the combined rank of the dyad, whether the dyad involved any immigrant females, whether the dyad consisted of females related to each other, and the total time the dyad was in the same party when one of females was the focal. For analysis 2 (partner selection analysis), data is organized per dyad at each coalition event. This dataset includes relevant information about the dyad as in analysis 1, but also indicates which dyad formed the coalition out of all available partners at the time of the coalition event.