RESPONSES OF SONGS SPARROWS TO SONG-TYPE MATCHING VIA INTERACTIVE PLAYBACK

The aggressive and singing responses of ten territorial male song spar rows, Melospiza melodia, to sustained song-type matching via interacti ve playback were examined. This auditory stimulus, which involves both synchronous switching and song-type matching, was hypothesized to be a strong aggressive threat. Responses were compared to five other tria l types in which the switching pattern and song-type similarity were i ndependently varied. The six trial types were organized into a factori al design with three switching levels (no switching, synchronized swit ching, and rapid unsynchronized switching) and two matching levels (sh ared song-types and unshared song-types). The aggressive response of t he birds, a composite index of the correlated behaviors of singing rat e, perch change rate, and time spent close to the speaker, showed sign ificant main effects of both the switching and the matching factors, w ith no interaction effect. The response was highest for the shared/uns ynchronized switching trial and lowest for the unshared/no switching t rial. Since the synchronous switching trials produced aggressive respo nses intermediate between the no switching and rapid unsynchronized sw itching trials, our results corroborate earlier studies showing that s witching rate, song-type diversity and song similarity are the key det erminants of aggressive approach. However, the switching rate of the f ocal birds during playback was not correlated with the other response variables and showed a very different pattern from the aggressive resp onse. Switching rate increased during unshared/synchronized trials and decreased during shared/synchronized (i.e., song-type matching) trial s. The tendency of the birds to refrain from switching when they were song-type matched by playback led to long bouts of matched-type counte rsinging. These results suggest that song-type matching locks two coun tersinging birds into a new level of interaction in which information other than aggressive motivation is exchanged.