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(詳細はthumb Most owls are nocturnal or crepuscular birds of prey. Because they hunt at night, they must rely on non-visual senses. Experiments by Roger Payne〔Payne, Roger S., 1962. How the Barn Owl Locates Prey by Hearing. ''The Living Bird, First Annual of the Cornell Laboratory of Ornithology'', 151-159〕 have shown that owls are sensitive to the sounds made by their prey, not the heat or the smell. In fact, the sound cues are both necessary and sufficient for localization of mice from a distant location where they are perched. For this to work, the owls must be able to accurately localize both the azimuth and the elevation of the sound source. ==ITD and ILD== Owls must be able to determine the necessary angle of descent, i.e. the elevation, in addition to azimuth (horizontal angle to the sound). This bi-coordinate sound localization is accomplished through two binaural cues: the interaural time difference (ITD) and the interaural level difference (ILD), also known as the interaural intensity difference (IID). The ability in owls is unusual; in ground-bound mammals such as mice, ITD and ILD are not utilized in the same manner. In these mammals, ITDs tend to be utilized for localization of lower frequency sounds, while ILDs tend to be used for higher frequency sounds. ITD occurs whenever the distance from the source of sound to the two ears is different, resulting in differences in the arrival times of the sound at the two ears. When the sound source is directly in front of the owl, there is no ITD, i.e. the ITD is zero. In sound localization, ITDs are used as cues for location in the azimuth. ITD changes systematically with azimuth. Sounds to the right arrive first at the right ear; sounds to the left arrive first at the left ear. In mammals there is a level difference in sounds at the two ears caused by the sound-shadowing effect of the head. But in many species of owls, level differences arise primarily for sounds that are shifted above or below the elevation of the horizontal plane. This is due to the asymmetry in placement of the ear openings in the owl's head, such that sounds from below the owl reach the left ear first and sounds from above reach the right ear first.〔Knudsen EI. 1981. The hearing of the barn owl. Sci Am 245(6):113-25〕 IID is a measure of the difference in the level of the sound as it reaches each ear. In many owls, IIDs for high-frequency sounds (higher than 4 or 5 kHz) are the principal cues for locating sound elevation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sound localization in owls」の詳細全文を読む スポンサード リンク
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