Monday, August 27, 2012

Ultrasonic Bird Control? Don't Throw Your Money Away!

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.

Birds, on the other hand, usually hear best between 1-5 kHz, with total hearing between .5 and 8 kHz.  There is a huge amount of variation between species.  Some songbirds—especially those with high pitched songs—can hear up to about 20 kHz.  There are some discrepancies in studies of the upper limits of bird hearing, but in the most recent tests, no birds have been shown to hear frequencies above 20 kHz.  Even birds like oilbirds and swiftlets that are known to use sound for echolocation in dark caves only use audible sounds between 1 and 15 kHz. For this reason, ultrasonic devices using frequencies between 15-30 kHz are completely ineffective save for a few songbirds.

While birds may not hear higher frequency sounds any better than people do, a few including pigeons and owls may actually hear lower frequency sounds better.  In 1979 researchers discovered that some pigeons can hear sounds as low as .05 Hz.  That's the kind of low infrasounds created by earthquakes, winds over distant mountains, or waves on distant shorelines.  Some researchers have speculated that these birds can use these distant sounds to help them maintain a general sense of direction.

So before you buy an ultrasonic bird scaring device costing several hundred dollars, remember this general rule: most birds hear about as good as you do—even with your middle-age hearing loss!