Written By: Rob Fergus, Ph.D.
Sometimes hardware or lawn & garden companies advertise ultrasonic devices that are supposed to drive birds away with high frequency noises undetectable to humans. Sounds like a good idea, right? Blast out sounds birds can hear but we can’t—what’s not to like? Unfortunately, the truth is that birds do not actually hear these ultrasonic sounds any better than humans do, and there is no scientific evidence that these devices actually work. The bottom line is that birds cannot hear ultrasonic frequencies and ultrasonic devices don’t work.
Humans hear sounds between the frequencies of about 20 to 20,000 acoustical vibrations per second (hertz or Hz). Middle C is about 262 Hz and the highest piano key (C8) is about 4186 Hz. As you get older, you lose the higher frequency sounds; middle-aged people can often hear sounds only up to 12,000-14,000 Hz (12-14kHz). High frequency dog whistles work because dogs can hear sounds up to 40-60 kHz. Bats use sounds up to 100 kHz to help them locate their flying insect prey and avoid obstacles in the night sky. (more…)