On a list of very loud sounds, birdsong would probably land very near the bottom. Of course, anything could hurt your ears if it was amplified enough, but you wouldn’t normally expect to be cowering before the almighty screech of a robin. With good reason, perhaps. Except squeakiness: a robin’s song, at a reasonable volume, approaches notes so high they’re near the limits of human hearing. The robin in this recording is singing as high as 10kHz, but its overtones (high-pitched resonances) go up to about 17kHz, which is about as high as most humans can hear.
Do you ever hear anything else that high-pitched? Maybe the occasional worn out vehicle brakes or emergency sirens, but there aren’t that many other examples. The standard theory for why birds sing high-pitched songs in cities is that it helps them avoid auditory ‘masking’, where sounds in the same frequency range interfere with each other. Masking is the reason why you wouldn’t be able to hold a spoken conversation in the same room as someone playing a tenor saxophone, for example: the instrument occupies almost the same frequency range as the human voice.
The newer theory about this is that birds in high-traffic areas are actually just trying to sing louder, which happens to be easier for them at higher pitches—again, curiously enough, like a saxophone. A 2013 study of 45 blackbirds found that the volume of their songs correlated strongly with pitch, and argued that volume is actually the most acoustically efficient way for birds to overcome additional background noise.
If anything, the gradual electric car takeover in the world’s wealthier cities will quieten their streets, and we might then be able to settle this question: will birds breathe a sigh of relief and lower their volume again, reducing their pitch as a side effect, or will they predominantly use pitch as their anti-masking tool and continue to fit it around other sounds? Whichever is the case, this robin’s song costs time that it could spend looking for food, so we will continue to love birds for singing anything at all. º
by Jay Richardson
Friday 27th May 2022