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A deer horn, or deer whistle, is a (whistle) mounted on automobiles intended to help prevent collisions with deer. A Shu-Roo is a similar device used in Australia to scare off kangaroos. Air moving through the device produces ultrasound or other high-frequency sound waves, intended to warn deer of a vehicle's approach. Deer are highly unpredictable, skittish animals whose normal reaction to an unfamiliar sound is to stop, look and listen to determine if they are being threatened.
Scientific studies of these devices have indicated that they do not in fact reduce collisions.
- Some deer whistles do not emit any ultrasonic sound under the advertised operating conditions (typically when the vehicle exceeds 30 mph).
- Ultrasonic sound does not carry very well. It does not travel a long enough distance to provide adequate warning, and also is stopped by virtually any intervening object, so any curves in a road will block the sound.
- Little is known about the auditory limits of deer, but current knowledge indicates that deer hear approximately the same frequencies as humans, and thus if humans can't hear a sound, deer probably can't either.
- If deer could hear ultrasound, it is unknown if it would alarm them or induce a flight response. Certainly if they heard it on a regular basis, they would get used to the sound and not react to it.
In addition to the Georgia and Wisconsin studies, a study by the Ohio State Police Department also indicated the whistles are ineffective. Independent testing carried out by the Department of Zoology at the University of Melbourne reached the same conclusion about shu-roos and kangaroos.
- "Blowing the Whistle on Deer Scare Devices", Farm Journal, Mid-February 1993 issue.
- Schwalbach, Randall P.: Whistles and Whitetails, Deer and Deer Hunting, Nov. 1989.
- Insurance Institute for Highway Safety Advisory #31
- An article from Road Management and Engineering Journal