The function of distress calls given by tufted titmice ( Parus bicolor): an experimental approach

Abstract

I studied the response of tufted titmice ( Parus bicolor) to distress-call playbacks to discern the function of distress calls given in a non-breeding context. At baited locations, titmice were presented with three different stimuli: (1) a hawk model, (2) a distress-call playback, and (3) a hawk model in association with a distress-call playback. The reactions of titmice to these stimuli were measured in terms of the number of titmice attracted to the stimuli, time spent by titmice in the area around the stimuli, and the number of visits made by titmice to the area around the stimuli. Titmice approached closer to and spent more time near the source of the distress call when the call was not associated with a hawk model than when a hawk model was present. In either case, the approach of titmice was slow and cautious. Exposure to a hawk model in the absence of a distress-call playback caused titmice either to mob the model or ignore it. Titmice recognized the hawk model more often when it was associated with a distress-call playback than when it was presented alone. These observations are in accordance with predictions of the hypothesis that distress calls warn other birds of danger. Conversely, many observations contradicted the hypothesis that distress calls are calls for help.