We developed a new method to estimate the auditory abilities of animals using responses elicited by the presentation of auditory stimuli, without restraining or training the subjects. Using this method, we examined the hearing ranges of four raptors (a Mountain Hawk-eagle Spizaetus nipalensis, Northern Goshawk Accipiter gentilis, Common Buzzard Buteo buteo, and Grey-faced Buzzard-eagle Butastur indicus) kept in Ueno Zoo, in Japan, by presenting pure tones and white noise at two sound-pressure levels. Unconditioned responses, such as pupillary dilation and physical movements, were observed in all subjects. We then presented paired video clips of the raptors, with and without auditory stimuli, to human assayers, who were asked which clip contained the auditory stimulus. The accuracy of the human perceptual assay (HPA) suggested that the Mountain Hawk-eagle and Northern Goshawk hear frequencies from 1 to 5.7 kHz best, which is comparable to the results of an experiment with an American Kestrel Falco sparverius and European Sparrowhawks Accipiter nisus. The assayers reported that they used movements of the neck, head, and eyes, and changes in the pupils of the raptors as critical cues. Our method reliably reflected the hearing ranges of the raptors, and should be helpful for estimating the auditory capabilities of rare animals, such as the Mountain Hawk-eagle studied here.

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