An experimental study of ecological constraints in the cooperatively breeding acorn woodpecker

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The mating system of the acorn woodpecker (Melanerpes formicivorus) is among the most complex of any vertebrate, with groups consisting of a breeding core of up to seven cobreeding males and three joint-nesting females mating together (cooperative polyyamy or polygynandry) in combination with a variable number of nonbreeding helpers that are offspring from prior years and that have delayed dispersal to remain on their natal territory. Cobreeders of the same sex are almost always close relatives, either siblings or parents and offspring. The project will experimentally test the role of roosting and nesting cavities and of storage facilities in which groups store acorns as ecological constraints leading to delayed dispersal by offspring and cooperative polygamy by same-sex coalitions of relatives. The project will involve a thorough survey of cavities and storage facilities of existing groups and an experiment in which artificial cavities and storage facilities will be provided in previously unused areas. The incidence and rate of colonization of experimental sites compared to control sites, together with the origin and identity of colonists, will be used to accept or reject these hypotheses. The project will provide new insights into the role of ecological constraints to the evolution of cooperative breeding, including not only delayed dispersal and helping at the nest but also cooperative polygamy. The project will focus specifically on the interactions between ecological constraints, social factors such as group size and composition, and variation in territory quality as factors influencing these social phenomena.The project encompasses significant public outreach, particularly with respect to informal talks and demonstrations regarding acorn woodpeckers made to visitors and students at the field site, Hastings Reservation. The latter include minority, underrepresented, and urban students spending time at Hastings Reservation as part of a major NSF-funded GK-12 program. The project includes a significant educational component in the form of postdoctoral training and the training of up to five undergraduate students per year who will directly participate in the research. The study involves work in California oak woodland, a threatened habitat known for its biodiversity, and continues a long-term project that contributes to our knowledge of how ecosystems are affected by human-induced changes.