YOUNG, R.*; JAWOR, J.; KETTERSON, E.; Indiana University, Bloomington; Indiana University, Bloomington; Indiana University, Bloomington: Hormonal correlates of aggressionand dominance in female juncos

Aggressive behavior in male birds is well studied; males may sing at, approach, or attack intruders, and these behaviors are linked to a rise in testosterone. Female birds exhibit many of the same aggressive responses towards intruding conspecific females, but the hormonal basis of female aggression is not fully understood. Also not well understood are the relationships among aggression, hormones and monogamy. We studied a captive population of dark-eyed juncos (Junco hyemalis) in a simulated intruder situation. An intruder female was introduced to a bonded male-female pair. Behaviors, testosterone titers and corticosterone levels were monitored in both females and in the male. We began the experiment by taking baseline blood samples for testosterone and corticosterone from both females. We next introduced the male into a breeding aviary along with a female, hereafter the resident female, and the pair was given a 2-day adjustment period. A second baseline blood sample was taken before introduction of the intruder female, and behavior was monitored closely for 30 minutes, after which a third blood sample was collected. Males had usually bonded with resident females by the time the intruder was introduced, but they still courted the intruders and became aggressive only if the intruder behaved aggressively towards them. As predicted, resident females dominated the intruders in all but one case. Preliminary research with this species had indicated that dominant females are more likely to breed, and this held true in all cases, even the one in which the intruder became dominant over the resident. Hormonal assays are pending and will reveal whether female status as resident or intruder is hormonally linked and, if so, whether female testosterone might play a role in the maintenance of monogamous mating systems.