![]() Dice (1945) calculated the minimum intensities of light required by the barn owl ( Tyto alba), the long-eared owl ( Asio otus), the barred owl ( Strix varia), and the burrowing owl ( Speotyto cunicularia) to see a dead mouse from a distance of 6 ft. Work prior to that time had suggested that, in the wild, light levels must often fall below that at which owls can see their prey, thus forcing them to rely upon some non-visual sense in hunting. Though Pumphrey (1948), Southern (1955) and others have suggested that the asymmetrical ears of owls may be useful in hunting, prey location by hearing was first demonstrated by Payne & Drury (1958). Although the asymmetry may involve the modification of different structures in different species ( Stellbogen, 1930) the result is usually the same: one ear has its opening above the horizontal plane, the other below it. The external ears of many species of owls are asymmetrical ( Ridgeway, 1914 Stellbogen, 1930). Movements of a flap of skin in front of the ear opening changes the overall directional sensitivity patterns by redirecting the regions of maximum sensitivity.Ī theory is presented to explain how a barn owl might locate the position of a sound source by moving its head until the intensity of all frequencies comprising a complex sound is brought to a maximum in both ears (aided perhaps by differences in inter-aural time delay that are enhanced by intensity disparities). These regions of good sensitivity are correlated with the asymmetry of the barn owl’s external ears. At such frequencies, regions of high sensitivity (tightly isolated by peripheral regions of low sensitivity) are directed along different paths for the two ears. Measurements of sound pressure in the region of the owl’s eardrum, made with a probe-tube microphone while moving a loudspeaker around the owl’s head, reveal that for frequencies above 8-5 kHz the ear is highly directional. Barn owls ( Tyto alba) can locate prey in total darkness using only the sense of hearing, with an error of less than 1° in both the vertical and horizontal planes.ĭifferences between the behaviour of barn owls flying at prey in complete darkness (analysed from films taken under infra-red illumination) and their behaviour in the light are correlated with the problems they must face in acoustic orientation.Įxperiments with owls trained to strike a concealed loudspeaker show that they depend on frequencies of sound above 5 kHz.
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