MALUEG, A. L.*; MOORE, I. T.; WALTERS, J. R.; Virginia Polytechnic and State University; Virginia Polytechnic and State Univeristy; Virginia Polytechnic and State University: Hormonal differences between helpers and breeders in a cooperatively breeding bird

Red-cockaded woodpeckers (Picoides borealis) are cooperative breeders, living in family groups that consist of a breeding pair and zero to five non-breeding helper males. Helpers do not copulate nor father any offspring. They do, however, assist the breeding pair in territory defense, cavity construction and maintenance, and care of offspring, including feeding and incubation. While theories for the ultimate causes for this breeding strategy have been proposed, there is little data to explain a proximate mechanism driving helping behavior and accompanying lack of sexual activity. Previous studies have shown that helpers and breeders in this species have similar levels of testosterone and prolactin. However, studies in other species have found that concentrations of the stress hormone corticosterone often differ between individuals of different social status, and corticosterone is well known for its inhibitory effects on reproductive function. From July 15 to August 18 of 2005 we collected preliminary blood samples from nine breeding males and five helper males living on Marine Corps Base Camp Lejeune in Jacksonville, North Carolina. We are investigating whether the observed differences in sexual behavior in male red-cockaded woodpeckers may be attributed to differences in corticosterone concentrations.