Every time I see a car (or more likely, a truck) with a deer whistle I wonder what motivated the owner to buy it, and if there’s any reason to think they work. I assume the efficacy of deer whistles has be determined largely based on anecdotal evidence, not science.
It turns out a surprising amount a scientific thinking has been applied to deer whistles, and the results, while not exactly conclusive, don’t surprise me much. I came across an article on the subject in Improbable Research.
The paper, Analysis and effectiveness of deer whistles for motor vehicles: frequencies, levels, and animal threshold responses, is only 6 pages and fairly easy to read.