Female-female territorial aggression and its hormonal control in the song sparrow

Thesis (Ph. D.)--University of Washington, 1997The function, seasonality and hormonal control of aggression among male conspecifics have been well studied in many taxa. In most cases, female-female intraspecific aggression has been less well studied. Male song sparrows are aggressive all year in resident populations, but levels of testosterone correlate with aggression only during periods of social instability. The seasonal pattern and possible hormonal correlates of female aggression are unknown. Female-female aggressive responses are similar to males' and include flights, threat vocalizations, wing waving and posturing. Possible functions, seasonal differences and hormonal underpinnings were tested with a series of field and laboratory experiments. To investigate function and hormonal control of female-female aggression, at two field sites in Western Washington, either a live caged female song sparrow and playback of female calls, or the control, a Rufous-sided Towhee mount and Towhee vocalizations, were presented to females on their territories in the spring prior to breeding, while the female was incubating, or in the fall following the molt. Females responded more to simulated song sparrow intrusion than to towhee presentations in all seasons. Female-female aggression was highest in spring and decreased across the breeding and post-molt (fall) seasons. Female-female aggression appeared to function to protect a female's monogamous status and access to paternal care, food and nest sites on the territory. At one site, females removals suggested that there were few female floaters. Blood samples taken following the simulated female intrusions were compared to those taken from passively netted females during the same season. Passively netted females had significantly higher levels of testosterone and dihydrotestosterone than females experiencing simulated female song sparrow intrusions in the field. There were no significant differences in circulating estradiol, progesterone or corticosterone. To test possible hormonal control of female-female aggression directly, captive females were ovariectomized and given hormone implants then behaviorally tested in single aviaries. There were no significant differences in behavioral response to simulated female intrusion in captive females given either an empty, estradiol or testosterone filled implant. These data suggest that androgens do not activate female-female aggression in song sparrows. Comparisons to data on male song sparrows are discussed