Date of Award

Spring 2021

Document Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences


Ecological Sciences

Committee Director

Eric L. Walters

Committee Member

Walter D. Koenig

Committee Member

Holly Gaff


Dispersal is a critical life-stage with consequences not only for the individual, but for population dynamics and thus the fate of the whole species. The creation of dispersal coalitions can lead to complex outcomes and affect how changes in abundance occur on the landscape. I examined population dynamics and dispersal coalitions in a population of cooperatively breeding acorn woodpeckers in central California, USA. Using a 34-year dataset on occupancy and abundance, I determined that increases in abundance were determined by dispersal to new locations. This resulted in increased occupancy, rather than increases in group size and larger coalitions. I then examined vocal recruitment via simulated breeding vacancy conflicts to determine whether vocal signaling was sufficient to recruit individuals to a simulated conflict. Despite using recordings of conflict vocalizations, individuals exhibited a territorial response to these simulations, rather than responding as if to a breeding vacancy. Finally, I examined observed coalition sizes during breeding vacancy conflicts relative to those inferred from historical records of group composition following breeder turnover. Coalition dissolution after the conclusion of an observed conflict was common in non-breeders, suggesting that indirect fitness benefits are a major driver of coalition participation. Surprisingly, individuals with breeding positions often participated in these conflicts but did not remain with the coalition following the successful acquisition of the new breeding position. This flips the paradigm of cooperative breeding, with helping behavior directed from breeders to their non-breeding kin and offspring, thus leading breeders to gain indirect and direct fitness benefits through improving the reproductive success of their so-called "helpers". Overall, as resources increase, the population expands by taking advantage of previously marginal habitat in non-combative dispersal events, primarily by single individuals rather than coalitions. Marginal habitat does not appear to attract coalition visits, even with simulated vocalizations of dispersal conflicts. Dispersal conflicts occur primarily at high-quality habitat and involve the majority of same-sex relatives residing at the home territory, even those with breeding positions.


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