Does song deter territorial intrusion in White-throated Sparrows (Zonotrichia albicollis)?

The role of the song of the White-throated Sparrow (Zonotrichia albicollis) as a deterrent to potential intruders was assessed by removing territorial males of the white-striped morph and replacing them with loudspeakers playing back their songs. Following removals, intrusions of new singing birds were both delayed and fewer in inner zones of playback territories, as compared with similar areas of control territories that had no playback. In peripheral zones (outside the area defined by loudspeakers), or after playback ended (after 2 days), there were no significant differences between playback and control territories. During the playback period, intrusions were reduced within 10 m of speakers but not at greater distances. Thus, song tends to inhibit territorial intruders from singing and thereby asserts the resident male's dominance. To achieve this effect, I suggest that a resident needs to sing to some extent throughout its territory. These results are compared with those obtained in studies of the Great Tit (Parus major).