Avian flight III: hummingbird flight

Hummingbirds are amazing fliers. They fly forward at up to 26 miles per hour; they fly backward; they hover. They beat their wings 50 times a second, so all you see is a blur, with that enameled little body floating serenely in the middle. They are flight acrobats. They are flight artistes. How do they do that?

Rufous Hummingbird. Photo by M. LaBarbera

Rufous Hummingbird. Photo by M. LaBarbera

It helps that they are quite small. The amount of power that you can get out of your muscles increases as muscle mass (size) increases—bigger muscles, more power—but the amount of power increases less quickly than mass does. That is, if you double the size of the muscle, you get less than twice the amount of power out of it. This means that as an animal gets bigger, its ratio of muscle power to muscle mass decreases. An ant can carry enormous things for its size. A small bird can generate enough power with its muscles to hold its own body aloft and still in the air—to hover. A California Condor? Not so much. Hummingbirds’ small size means that they are, relative to their own body mass, very strong.

Rufous Hummingbirds are small. Photo by M. LaBarbera

Small size is a Rufous Hummingbird’s secret weapon.
Photo by M. LaBarbera

They are also built rather differently from other birds, specialized for their aerial lifestyle. Their legs are extremely short: there’s no point carrying around the extra weight of long legs if you won’t ever need to walk. The structure of the joint where their wing connects to their body is specialized for the large range of wing motions that hummingbirds use. It is this variation in wing motion that lets hummingbirds move in all directions so well.

The following slow-motion video lets you get a better look at how the wings move. Watch for the change in wing motions as the bird changes direction: in hovering flight, the bird’s wingtips trace out a horizontal figure-eight in the air, while when the bird moves backwards or forwards, the wingtips trace out ovals at different angles.

That figure-eight motion of the wings is key to the hummingbird’s phenomenal ability to hover. Most flapping birds generate lift on the downstroke of the wings but not on the upstroke, the same way that when you paddle a canoe, you move the canoe forward on the initial stroke, but don’t generate any thrust on the recovery stroke. A hovering hummingbird, however, generates lift both on the forward stroke and on the backstroke of its wings. That figure-eight wing motion keeps the wings relatively horizontal, and so generating upward force, all the time, so the hummingbird can stay still in the air rather than bobbing up and down.

(It’s not perfect: the backstroke generates only one-third of the lift that the forward stroke generates [Warrick et al. 2005]. But it’s better than nothing!)

This very-slow-motion video clearly shows the figure-eight wing motion:

Notice that on the backstroke, the wing is essentially turned upside-down: the feathers trailing the leading edge flip around so that what was the “top” of the wing on the forward stroke is now the “bottom” for the backstroke. That’s a pretty neat trick.

Upside-down wings! Photo by Bill Gracey*

Upside-down wings!
Photo by Bill Gracey*

Possibly the most impressive thing about hummingbird flight is that not only can they beat their wings 50 times per second, hover, and fly backwards, but on top of all that, they do so many other things that make flight even more challenging. They chase and fight each other in midair. They grow long ungainly tails to impress females. They live on mountaintops where the thin air is even less willing to hold them up. They are not fragile, about-to-fall-out-of-the-sky jewels; they are pugnacious little helicopters.

All this aerial mastery stuff is too easy, so I figured I'd add a huge tail. Long-tailed Sylph; photo by Francesco Veronesi*

All this aerial mastery stuff is too easy, so I figured I’d add a huge tail.
Long-tailed Sylph; photo by Francesco Veronesi*

Here is an Anna’s Hummingbird hovering in increasingly heavy rain. You can see that its body orientation changes, but it has no problem staying airborne or staying still enough to continue feeding. (Video from Ortega-Jimenez & Dudley 2012a.)

And once the rain stops, you have to get that water off somehow—why not enjoy a vigorous full-body shake while flying? An Anna’s Hummingbird demonstrates. (Video from Ortega-Jimenez & Dudley 2012b.)

Admittedly, the shakes seem to be even more vigorous when the bird doesn’t have to worry about staying airborne too. (Video from Ortega-Jimenez & Dudley 2012b.)

References:

Gill FB. 2007. Ornithology, 3rd ed. New York: W.H. Freeman & Company.

Ortega-Jimenez VM, Dudley R. 2012a. Flying in the rain: hovering performance of Anna’s hummingbirds under varied precipitation. Proceedings of the Royal Society B 279:3996-4002.

Ortega-Jimenez VM, Dudley R. 2012b. Aerial shaking performance of wet Anna’s hummingbirds. Journal of the Royal Society Interface 9:1093-1099.

Warrick DR, Tobalske BW, Powers DR. 2005. Aerodynamics of the hovering hummingbird. Nature 435:1094-1097.

*Photos obtained from Flickr and used via Creative Commons. Many thanks to these photographers for using Creative Commons!

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5 thoughts on “Avian flight III: hummingbird flight

  1. Are there any studies of how quickly they can pick up speed or change direction? What amazes me is that they seem to be able to dart: to go from absolutely still to too-fast-to-see-where-they-went. I expect that ability is related to being so small?

    • Sorry for the delayed response – still looking for a proper answer to this! Intuitively, I think you’re right that being small helps: small mass means lower momentum, so it’s easier to stop, start, and turn quickly. Being able to fly backward probably also helps when stopping suddenly: where other birds mostly use gravity and drag to stop, hummingbirds can actively cancel out their forward momentum by creating some backward force.

  2. Pingback: What do birds do when it rains? | Tough Little Birds

  3. The hummingbird was waiting as I hung my feeder for the first time last week. She was feeding frequently and often just sitting at the feeder. I imagine tired from her long trip. The past few days, blasting wind, low 40’s, and continuous rain. She continued to sit at the feeder in the rain and wind. It was so cold! Today it is calmer. I put fresh solution out. I have not seen her once. Now Im fearing she is sick from the cold, drenching, continuous wind. Is that possible?
    Worried in Lake Shore, MN

    • It is possible that she got too wet and cold. Hummingbirds are able to put up with pretty incredible conditions, though; I wouldn’t assume the worst. It may be that she’s taken this first nice day as an opportunity to fly around a bit – find some other food sources, look for a mate, look for a nesting spot.

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