A few years ago, the Colorado State Patrol did several well defined tests on the deer whistles. The results: there was no idication that the deer ever heard the deer whistles, and close calls and deer hits were the same with and without the whistles. They recommended that you don't waste your money and don't trust the whistles to keep deer away.The Ohio State Patrol, The Georgia State Patrol and the Insurance Institute for Highway Safety tested deer whistles. They don't work!
https://www.thecherrycreeknews.com/content/view/1678/104/
https://www.coloradolaw-blog.com/2006/10/be...mbi_threat.html
https://adm.idaho.gov/insurance/risk/newsle...visor_v3-02.pdf
The University of Wisconsin Study says they don't work.
Articles in Road Management and Engineering say they don't work.
There is not one, independent study that shows they work. There are dozens that show they don't.
Motorcycle Consumer News reviewed studies and concluded that they don't work.
There is no research to show deer are startled by sound at any particular frequency or decibel level (DeNicola et al. 2000). One study showed that deer whistles did not alter deer behavior enough to prevent them from crossing highways (Romin and Dalton 1992).
"Deer whistles and ultrasonic devices will not help prevent car collisions with deer." Best Practices for Nuisance Wildlife Control in New York State.
Enough?
Don't trust anecdotal evidence like "Uncle Billy says they have saved his life many times." There is no way Uncle Billy could know one way or the other.
Ron