Heterospecific responses to scream calls and vocal mimicry by phainopeplas (Phainopepla nitens) in distress

Using playback experiments, I tested whether distress calls by phainopeplas attract heterospecifics and elicit mobbing of a predator decoy. Phainopeplas use two types of distress calls: loud scream calls and mimicry of other species' vocalisations. Screams and imitations together attracted significantly more heterospecifics than in the absence of distress calls. When broadcast alone, scream calls were more effective at eliciting heterospecific approach and mobbing behaviour than were imitations. Birds were significantly more likely to mob the predator decoy during broadcast of screams and imitations than during broadcast of screams with digitally scrambled imitations, even though there was no significant difference between treatments in the number of birds initially approaching. This suggests that precise mimicry does not play a key role in attracting heterospecifics but may elicit increased mobbing once they have arrived. Mimicry did not appear to be directed at the species whose calls were imitated; only 4 of the 19 species responding to distress calls were model (mimicked) species, and birds mobbed the predator decoy regardless of whether imitations of their own calls were used in playback trials.