There have been many studies conducted in recent years testing the effectiveness of deer whistles used to prevent deer-vehicle crashes. The Wisconsin Department of Transportation funds the Deer-Vehicle Crash Information Clearinghouse (DVCIC), a center that compiles statistics about deer-vehicle crashes in the Midwest.
Center Director Keith Knapp recently reviewed many deer-vehicle crash deterrents, including deer whistles, and found that although effective at times, many whistles emit sounds outside the sensitivity of deer noise ranges. When the sounds are at the wrong frequency, deer are not able to hear the noise and avoid the cars. Knapp also found it was difficult for deer to hear some whistles when combined with everyday road noise.
For more information about deer whistles and deer-vehicle crashes in the Midwest, visit the Deer-Vehicle Crash Information Clearinghouse.