Accuracy of auditory distance and azimuth perception by a passerine bird in natural habitat.

Small birds should localize sound poorly because small head size limits azimuth resolution and because the loose correlation of acoustic degradation with distance limits accurate estimation of auditory distance. We determined the accuracy of sound localization by a passerine bird in the field using an open-loop phonotaxis experiment. After hearing a playback of a conspecific contact call, eastern towhees, Pipilo erythrophthalmus, approached the silenced source. Mean auditory distance resolution was 7% of total speaker distance and mean azimuth resolution was +/-5 degrees. In a second experiment, we played birds the same calls rerecorded previously over the 10- or 20-m distance beyond each playback location. In 13 of 30 trials, the birds over-flew the speaker by a distance propotional to rerecording; but in 15 trials, approach distances were comparable to speaker distance despite the addition of distance simulated by attenuating and rerecording the calls. Signal-specific and location-specific distance cues are derived to explain the bimodal distribution of flight distances we observed. Copyright 1998 The Association for the Study of Animal Behaviour