Physical parameters of sound that affect acoustic location in the barn owl (Tyto alba) were studied. The frequency of pure tone best suited for location was 7-8 KHz. Above and below this range, error of location increased. Tone bursts did not consistently give better location clues than sustained tones. Neither binaural phase nor time differences seem to be used for location. Results can be explained partly by assuming the use of binaural intensity differences. These owls located wide-band noises containing frequencies optimal for location more accurately than narrow-band and pure tone signals. Marler (1955) pointed out that some animal calls are more locatable than others. These two classes of sound differ from each other in their physical structure. Marler's nonlocatable signals are pure tones or narrow-band sounds, and his locatable animal calls contain wide spectra. Results presented here partly support Marler's predictions. However, in the barn owl, differences in locatability between the two classes of signals are not due to the reasons given by Marler for predators in general. If frequency characteristics of sound are used for location, the bandwidth of a signal is one of the major determinants of its value as a location clue. On this basis alone, the present results as well as Marler's hypothesis can be expected.
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文章 : 英语