LAUSR

In cooperative species, parental investment may be shared with auxiliaries. Kin selection and other types of benefits have been proposed to explain the evolution of helping behavior. Auxiliaries are expected to be more helpful when closely related to the breeders. In this context, breeders may adjust parental investment in at least three ways: (a) reducing their effort and being compensated by the auxiliaries’ investment (compensatory effect); (b) maintaining their effort, with an increase in total investment (additive effect); or (c) partial compensation, i.e., a decrease in care by the parents but not by as much as the increase in care from the auxiliaries. We studied the cooperative species Colaptes campestris campestris and tested the following hypotheses: (1) partial compensation effect occurs, (2) parents modulate their investment relative to the auxiliaries’ investment, (3) auxiliaries adjust their investment according to their relationship to the offspring, and (4) groups whose members are in better physical condition fledge more young or these are in better condition. We determined relatedness within groups and monitored parental and alloparental behavior during breeding. Breeders in cooperative groups presented the same investment as unattended breeders. Restricting the analysis to cooperative groups revealed that the investment made by auxiliaries reflected their relatedness to the young and positively affected the investment by breeders. Results suggest that a partial compensation occurs in the species, with breeders reducing their effort despite the small increase in overall nest investment. Results highlight the importance of kin selection in the evolution of cooperative breeding in campo flickers.Significance statementCooperatively breeding birds may have auxiliaries that help rear their brood. The evolution of helping behavior may derive from kin selection, where auxiliaries could gain a genetic benefit by helping to rear kin, which occurs when groups are composed of closely related individuals. However, it is often the case that some offspring may not be closely related to the auxiliaries due to the species’ mating system. We used the cooperatively breeding campo flickers to investigate whether and how the presence of auxiliaries might affect parental care patterns and nest productivity. We found that breeders did not reduce their investment in the presence of auxiliaries and that cooperative groups present the same overall investment when compared with unassisted pairs, indicating that the investment made by auxiliaries was not large enough to affect the total investment nor the breeders’ investment. Our results also show that auxiliaries increased their investment when they were more closely related to the brood.