Brooding, provisioning, and compensatory care in the cooperatively breeding acorn woodpecker

We analyzed reproductive investment in parental care (brooding and the provisioning of nestlings) in the acorn woodpecker (Melanerpes formicivorus), a cooperatively breeding species in which both polygynandry and helping-at-the-nest are common. As predicted based on the strategies pursued by birds of different sex and status, breeders generally invested more in parental care than helpers, and breeder females invested more than breeder males. Contrary to expectations, however, the degree to which individuals reduced their effort with increasing group size (i.e., patterns of load lightening or compensatory care) did not match overall investment. Instead, as group size increased, there was no significant difference in compensation in either brooding or provisioning among the different categories of birds. Compensation, at least by breeders, was significantly lower during the first week of the nestling period than later on, supporting the hypothesis that compensatory reduction in care is less likely when brood reduction is more common and was not affected by the acorn crop, which had no significant effect on the incidence of brood reduction despite being important to overall reproductive success. Our results offer support for the hypothesis that levels of compensation are influenced by the relative importance of brood reduction. More theoretical work, however, will be needed in order to understand the basis for patterns of compensation among individuals of different sex and status.