SPERRY, T.S.*; WINGFIELD, J.C.: Effects Of The Antiandrogen Flutamide Upon Territorial Aggression In Male Free-Living Song Sparrows

Male song sparrows, Melospiza melodia morphna, display territorial aggression in both breeding and nonbreeding seasons. Previous studies have demonstrated that estrogen plays a critical role in maintaining aggressive behavior in song sparrows. However, the role of androgens, acting via androgen receptors (AR), in regulating aggressive behavior in song sparrows is not known. Since blocking estrogenic effects does not completely inhibit aggressive behavior, it is hypothesized that a combined effect of androgens and estrogens releases the full repertoire of aggressive behavior during the breeding season. In order to test this, we implanted male free-living song sparrows with an antiandrogen (flutamide) and measured territorial aggression in populations living in Western Washington. These studies were conducted during the early breeding season when territories are being established and one month later prior to the first clutch being laid. Males were captured using mist-nets combined with conspecific playback and implanted with three 10mm silastic implants with or without flutamide. After 3 weeks, we returned to the territory and aggression was quantified using a 10 minute simulated territorial intrusion followed by 10 min observation. The results demonstrated that flutamide implants had no effect upon song rate, response latency or time within 5m of the decoy. However, there was a significant effect of the antiandrogen upon the number of flights associated with territorial aggression. This suggests that AR may mediate only one component of territorial aggression. We are conducting studies to determine whether this result is specific to territoriality or represents a nonspecific effect upon general activity.