Spatial association between females often mirrors pattern and strength of social relationships and cooperation within groups. Here we test for proposed differences in female-female associations and the role of sexual signaling between the two species of the genus Pan that have been linked to difference in female cooperation. Unlike previous studies, we found only limited evidence for a higher female-female gregariousness in bonobos. While bonobo females exhibited a slightly higher average number of females in their parties, there was neither a species difference in the time females spent alone, nor in the number of female party members in the absence of sexually attractive females. We found that the more frequent presence of maximally tumescent females in bonobos was associated with a significantly stronger increase in the number of female party members, independent of variation in food abundance. This indicates that conditions leading to changes in female sexual signaling ultimately affect female associations, potentially leading to marked behavioural differences between chimpanzees and bonobos. Our findings refute the idea that the higher gregariousness among bonobo females is driven by ecological factors alone and highlight that the temporal distribution of female sexual receptivity is an important factor to consider when studying mammal sociality.

This dataset has been collected at the field sites of LuiKotale, DRC and Taï, Cȏte d’Ivoire , between February 2015 and December 2017. We relied on female focal individual follows to reduce the bias towards larger groups stemming from party follows and be better able to quantify the durations individuals spend alone. We followed focal animals daily in two chimpanzee communities (Taï East and Taï South) and one bonobo community (Bompusa). We included all adult parous females at the start of our study period as our focal individuals (estimated older than 13 years). In the dataset there are the following columns:

Focal id, species, date (as character), halfday of follow, average number of female party members during focal follow, number party observation (conducted cumulative over 30 min), number of maximal tumescence females present in categories (see manuscript for categorization), percentage time spent in party with at least one maximally tumescent female, percentage of time spent with only females, percentage alone, monthly proportion of awake time spent feeding.