Female robins aggressively defend territories and sing during the non-reproductive wintering phase. During this time plasma levels of testosterone are elevated in free-living females. We investigated if testosterone activates aggression and song by application of the antiandrogen flutamide to captive females during the non-reproductive wintering phase and of testosterone at the begin of the reproductive spring phase. Antiandrogen treatment during the winter phase did not inhibit aggressive behavior, and testosterone treatment during spring did not facilitate it. Although females were aggressive in winter they did not sing in the aviary. However, testosterone treatment in spring induced song. These results suggest that elevated winter levels of testosterone induce song but not defense of a territory in female robins.