Neighbour recognition by resident males in the banded wren, Thryothorus pleurostictus, a tropical songbird with high song type sharing

Several studies and reviews have suggested that the ability to discriminate between neighbours and strangers decreases as neighbour song repertoire size and song type sharing increase. We tested the recognition capabilities of territorial male banded wrens by comparing the aggressive approach responses of focal birds to three playback treatments: shared song types sung by an adjacent neighbour (neighbour song), shared song types sung by unfamiliar birds (mimic song), and unshared song types sung by unfamiliar birds (unfamiliar song). All three treatments for each male were broadcast from the same location on the territorial boundary shared with the appropriate neighbour. As expected, focal males responded nonaggressively to the neighbour treatment and aggressively to the unfamiliar song treatment. The approach response to the mimic treatment was statistically indistinguishable from the unfamiliar treatment and significantly higher than the neighbour treatment, suggesting that most males were able to recognize unfamiliar singers even when the song types played were very similar to those of their neighbours. The relative strength of responses to the mimic varied: some males treated the mimic song with low aggression levels typical of responses to neighbour song. Repertoire sizes of focal and neighbour birds, the fraction of song types shared among neighbouring males, and the similarity of neighbour and mimic song types did not explain this variation. Therefore, within the short 3-min period of our playback experiments, some birds may have used repertoire composition as a recognition cue and confused the mimic with the neighbour.