I am fortunate in that there are a couple of hummingbirds that live near my home and I frequently get to see them hovering just outside my window, giving me a close-up view. This article looks at what we have learned about how the hummingbirds get their name.
The results reveal that aerodynamic forces produced as the wings move, together with the speed and direction of the wing movements, are largely enough to explain the hummingbirds’ hum.
The team note a crucial factor is the motion of a hummingbird’s wings. While most birds only create lift on the downstroke – found by the team to be the primary sound source – hummingbirds do so on the down and upstroke as a result of their unusual wing motion, which follows a path akin to a U-shaped smile. What’s more, these strokes occur much faster for hummingbirds – about 40 times a second. As a result, the team say, the hummingbird wing movement generates sounds at both 40Hz and 80Hz – sounds that are well within our hearing range and which were found to be the dominant components of the birds’ hum.
But variations of the forces within the strokes, together with further influence of the U-shaped wing motion, generate higher frequency overtones of these sounds.
“The lovely thing about the hummingbirds’ complex wingstroke is that those two primary pulses also cause even higher harmonics,” said Lentink, adding that such tones added to the timbre of the overall sound.
“It truly is the specific way that the forces fluctuate that creates the sound that we hear,” he said.
The team applied a simplified version of their theory to data for flying creatures from mosquitoes to birds like pigeons to reveal why their motion produces different sounds.
“It’s the way they generate forces that is different,” said Lentink. “And that causes why they whoosh versus hum, versus buzz, versus whine.”
They just don’t know the words.
It would be particularly odd if the wing motion didn’t produce overtones. That would only occur if the motion was perfectly sinusoidal. I don’t find any of this info to be new. I thought this was well understood. We get hummers at our house every summer and we have a couple of feeders. They can be particularly territorial and will dive bomb other hummers who venture too near to “their” feeder. Love to watch them and if they sneak up behind you, the sound can be startling.
The study wasn’t about understanding why there were any overtones at all, but about why they have the specific timbres that they do (i.e., why these sorts of patterns rather than something else). It’s of course not the case that every non-sinusoidal waveform sounds the same, and you obviously couldn’t explain what makes them different from each other by appealing to the fact that they all have the same property (of being non-sinusoidal).
@3
Not so much. A little Fourier analysis of the waveform will yield precisely which partials exist at specific frequencies and amplitudes, and from that, you can determine pretty well what they sound like, in qualitative terms, at least with some knowledge of human hearing. The wave shape is the timbre. The are inseparable.
Saying that you’ve come up with a mathematical model of the wing forces that produces an accurate rendering of the acoustic pressure wave (i.e., wave shape) is what they did, but that doesn’t sound nearly as interesting to the lay person as talking about “the sound of a hummingbird’s wings”.
jimf:
Do you think this is correcting something I said?
In case you still haven’t noticed, this is “new information” to you. It isn’t something that was already “well understood” by you.
Seems like you didn’t get this when you wrote your comment #2. So what was that about?
I guess you could be talking about the Guardian article … or if not them, who? They didn’t actually talk like that. I think it was reasonably clear about the research, at least as news articles go.