I was wandering through the forest in western Washington when I heard a series of high-pitched, whistling bird calls. As I peered into the foliage, I finally made out the Cedar Waxwings that were making the sound. Another time, I was in southern Texas, along the Rio Grande border. Again, I heard birds singling some very high notes. In this case, they were followed by a series of lower notes and a distinctive two-tone call. I realized that I was surrounded by a number of Ruby-crowned Kinglets.
Since those experiences, I’ve often been out with friends who simply could not hear the very high-pitched sounds that some birds make. I’m blessed with good hearing, and even then these calls were quite high, requiring some concentration to make out.
That got me thinking. Just as chickadees can see into the ultraviolet, beyond anything humans can perceive, I wondered if birds had hearing ranges that extend beyond ours. So of course I Googled it.
First of all, I wanted to know what the typical range of human hearing is. Turns out that, although we vary as individuals, most people can hear sounds between 20 and 20,000 Hz. We are more sensitive to the lower end of this range. As we get older, it’s normal to experience some hearing loss, particularly at the higher frequencies. That explains why my (mostly older) friends couldn’t hear the birds I could.
While they rely heavily on their sense of hearing, birds are actually less sensitive than us primates, with an optimal range between 1,000 and 4,000 Hz, although they can hear pretty much the same frequencies that we can. As one would expect, this varies by species.
Waxwings and kinglets tend to be at the high end, reaching 8,000 Hz or even higher. They’re joined by other birds with high-pitched songs such as Brown Creepers, and many sparrows and warblers. The Blackpoll Warbler is a virtuoso, with songs rising to 10,000 Hz. This is still well within the range of a person with normal hearing.
What about animals with the ability to echolocate; how high can they hear? I was amazed to learn that dolphins and bats are able to hear frequencies up to 100,000 Hz! The few birds that use echolocation (including some cave-dwelling swiftlets and oilbirds) make sounds that are much lower—rapid chirps and clicks between 2,000 and 8.000 Hz that we too can discern.
What about the other end of the spectrum? Do birds hear lower notes than humans? The lowest sound made by a bird is the Dwarf Cassowary of New Guinea, whose calls have been recorded as low as 23 Hz, still within human hearing range. We don’t know if they can hear lower sounds than that. Compare that to the ability of whales, who can hear sounds as low as 7 Hz. (I ran into some disagreement over whether pigeons can hear lower notes than humans. Thesis, anyone?)
I was a bit disappointed to discover that hearing isn’t one of a bird’s superpowers. Or is it? While their range may be more limited than ours, birds are extremely sensitive to variations of sound, and excel at sound recognition. According to one article:
Birds are especially sensitive to pitch, tone and rhythm changes and use those variations to recognize other individual birds, even in a noisy flock. Birds also use different sounds, songs and calls in different situations, and recognizing the different noises is essential to determine if a call is warning of a predator, advertising a territorial claim or offering to share food.
Moreover, birds have perfect pitch, something few people can claim. They’re better at hearing very quiet sounds, ones we’d overlook; a hunting owl can hear the pitter-patter of a mouse beneath a layer of snow. They also hear shorter notes. Humans process sounds in bytes about 1/20 of a second long whereas birds discriminate up to 1/200 of a second. This means where we hear one sound only, a bird may hear as many as ten separate notes.
So it turns out that birds’ hearing is pretty impressive after all. Are we surprised?