Emma Brindley has investigated the responses of European robins to the songs of neighbors and strangers. Despite the large and complex song repertoire of European robins, they were able to discriminate between the songs of neighbors and strangers. When they heard a tape recording of a stranger, they began to sing sooner, sang more songs, and overlapped their songs with the playback more often than they did on hearing a neighbor’s song. As Brindley suggests, the overlapping of song may be an aggressive response. However, this difference in responding to neighbor versus stranger occurred only when the neighbor’s song was played by a loudspeaker placed at the boundary between that neighbor’s territory and the territory of the bird being tested. If the same neighbor’s song was played at another boundary, one separating the territory of the test subject from another neighbor, it was treated as the call of a stranger. Not only does this result demonstrate that _____________________________________________, but it also shows that the choice of songs used in playback experiments is highly important.
* robin: 울새 ** territory: 영역