The relationship of nestling qualities to survival and breeding strategies of cooperatively breeding American crows in Ithaca, New York

Cooperative breeding describes the scenario in which one or more individuals work together to help raise non-descendant offspring of a breeding pair. As of 2009, cooperative breeding is known to occur in ∼3% of all bird species. Individuals who help breeders care for their offspring include the offspring of the breeders, siblings of the breeders, or immigrants into the social group. The interest in cooperative breeders originates with the fact that individuals who assist the breeders often have delayed personal reproduction and have directed their efforts toward raising non-descendant kin. The evolution of this scenario depends upon several issues including: the relatedness of breeders to helpers, the change in productivity that results from helper effort, and whether helpers gain direct fitness benefits as a result of their prolonged association with the breeding pair. This thesis reports on three observational studies on the breeding biology of cooperatively breeding American Crows ( Corvus brachyrhynchos brachyrhynchos) in Ithaca, New York. I found that helpers in the American Crow population of Ithaca, New York, do not increase the number of nestlings produced in the broods they help, but do increase the quality of the young leaving the nest. Helper contributions are associated with trade-offs by the breeding pair that may improve overall nesting success in ways that were not directly assessed. Predicting which individuals will likely become breeders in this population was not based on the nestling characteristics of individuals, unlike the relationship often seen in short-lived bird species. Finally, the mouth color of nestlings near fledging-age is apparently related to individual age and does not correlate with potential hunger level or body temperature. Future studies on cooperatively breeding species will benefit from the research reported in this thesis because of the insights gained from the within-species, comparable study on helping behavior, the exploration of which factors influence the probability of becoming a breeder in a species where breeding dispersal is relatively constrained, and because my investigation of nestling mouth color as a signal of need is the first to be reported in a cooperatively breeding species.