Information transfer during mobbing: call rate is more important than the number of callers in a southern temperate passerine

Abstract

Abstract Many bird species vary their alarm calls according to the level of risk they face and this information can be used by receivers to respond to the mobbing event. Recent studies have also found that the number of callers can play an important role in the decision of subsequent individuals to join a mobbing event. We conducted a playback experiment to assess if differences in calling rate and number of callers elicit different behavioural responses in the house wren (Troglodytes aedon chilensis). We broadcast the alarm call of either one or two individuals, at different calling rates along the breeding season. We found that house wrens responded more frequently during playback of alarm calls at higher rates than during playback of calls at lower rates. However, focal individuals moved closer to the speaker when calls were played back at lower rates. There were no differences in the response of house wrens when we broadcast the calls of one or two individuals. These results suggest that call rates are an important element in the communication of danger in the house wren, rather than caller number.