STRONGER TERRITORIAL RESPONSES TO FREQUENCY-MODULATED COOS IN COLLARED DOVES

Playback experiments were used to investigate the perception of freque ncy variations in perch coos by collared doves, Stteptopelia decaocto. Territorial males responded more strongly to modulated than to unmodu lated coos. This effect was seen whether all three elements of the coo , or just the first element, were modulated. Modulated coos differed f rom unmodulated coos in two ways, first by an increased average freque ncy, and second, by the presence of a discrete change in frequency. We show that it was the change in frequency that was responsible for the level of response to modulated coos. The stronger responses to modula ted coos are interpreted as a result of the receiver rating the sender as a stronger competitor. (C) 1997 The Association for the Study of A nimal Behaviour.