Females cooperate, rather than monopolize reproduction, in multi-female groups of cooperatively breeding birds and...

Scholars have long sought to understand why, in some cooperatively breeding species, females care for the offspring of other group members while forgoing their own reproduction. Here, we analysed data from 101 cooperatively breeding populations of 73 bird and mammal species to advance research on this question. First, we illustrate the extent to which this question is relevant by mapping the substantial interspecific variation in the prevalence of multi-female groups (because only in these groups can females either compete or cooperate with respect to reproduction). Second, we show that in multi-female groups, females more often alloparent each others' offspring and share, rather than monopolize, reproduction. Third, we demonstrate the misleading effect of ignoring social composition when curating empirical data to test theoretical models of social behaviour by revisiting evidence presented to support the limited control model. Taken together, our findings uncover a high degree of reproductive cooperation in multi-female groups of cooperatively breeding birds and mammals. They thereby highlight the need for further research on the conditions that (i) favour the formation of multi-female groups (i.e. as a precondition for reproductive cooperation), and (ii) subsequently support the realization and maintenance of female cooperation once it becomes possible.