Mechanisms of sound localization in the barn owl (Tyto alba)

We investigated the mechanisms by which the barn owl (Tyto alba) determines the azimuth and elevation of a sound source. Our measure of localizing ability was the accuracy with which the owl oriented its head to a sound source. When localizing tonal signals, the owl committed the smallest errors at frequencies between 4 and 8 kHz. The azimuthal component of these errors was frequency independent from 1 to 8 kHz, but the elevational component increased dramatically for frequencies below 4 kHz. The owl's mean error when localizing wide band noise was nearly three times less than its mean error when localizing the optimal frequency for tonal localization (6 kHz). Occluding the right ear caused the owl to orient below and to the left of the sound source; occluding the left ear caused it to orient above and to the right of the sound source. With ruff feathers (facial ruff) removed, the owl continued to localize sounds accurately in azimuth, but failed to localize sounds in elevation. We conclude from these results that the barn owl uses interaural comparisons of sound spectrum to determine the elevation of a sound source. Both interaural onset time and interaural spectrum are used to identify the azimuth of the sound source. If onset time is not available (as in a continuous sound), the owl can derive the azimuth of the source from interaural spectrum alone, but its spatial resolution is poorer