Target-approaching behavior of barn owls (Tyto alba): influence of sound frequency.

We studied the influence of frequency on sound localization in free-flying barn owls by quantifying aspects of their target-approaching behavior to a distant sound source during ongoing auditory stimulation. In the baseline condition with a stimulus covering most of the owls hearing range (1-10 kHz), all owls landed within a radius of 20 cm from the loudspeaker in more than 80% of the cases and localization along the azimuth was more accurate than localization in elevation. When the stimulus contained only high frequencies (>5 kHz) no changes in striking behavior were observed. But when only frequencies from 1 to 5 kHz were presented, localization accuracy and precision decreased. In a second step we tested whether a further border exists at 2.5 kHz as suggested by optimality models. When we compared striking behavior for a stimulus having energy from 2.5 to 5 kHz with a stimulus having energy between 1 and 2.5 kHz, no consistent differences in striking behavior were observed. It was further found that pre-takeoff latency was longer for the latter stimulus than for baseline and that center frequency was a better predictor for landing precision than stimulus bandwidth. These data fit well with what is known from head-turning studies and from neurophysiology.