The Question

The hummingbird (scientific family: trochilidae) does not fly in the same way other birds do. They can fly forward, backward, up, down, and even upside-down. The motion of their wings changes its angle with each flap. Unlike other birds, hummingbirds flap their wings horizontally in the shape of a figure 8.  They also expand and contract their tail feathers, which allows them to hover in mid-air.

However, hummingbirds flap their wings like this on an average of 50 times per second, and during courtship they can flap their wings up to 200 times a second. So, to us, the motion of a hummingbird's wings is just a blur. This brings up an interesting question:

How do you measure the number of wing beats of a hummingbird?

The Answer: With high-speed photography and electronic flashes.

This question remained unanswered until the late 1950's. It was then that Crawford H. Greenewalt, an expert on hummingbirds, developed a method that allowed for the wing beats of a hummingbird to be captured on film. He designed a special kind of camera that starts instantly when a hummingbird flies into a beam of light, which shines onto a photo cell. What this means is that the bird basically takes its own picture. This whole process aided in the discovery of how a hummingbird flaps it wings and provided a way to count the number of wing beats. Now we know that the average hummingbird flaps its wings about 50 times per second.

Greenewalt also invented a way to measure the flight speed of a hummingbird. He made a wind tunnel with a feeder at one end and a fan at the other. He then placed a bird in the tunnel, revving the fan at varying speeds.

The Interview

(Excerpt from an email interview with Mr. Greg Scott, Hummingbird Photographer)

What is the best method when trying to find the wing speed of hummingbird wings?
-The best way to compute the wing speed of a hummingbird is to calculate it from the blur in a photo. If you know precisely the duration of the flash, this is an easy and direct calculation. 4. another way to calculate it would be to just measure the frequency of the wing beat (from an audio recording), and use the wing stroke geometry to calculate the length of the stroke. The AVERAGE speed easy to calculate. The Maximum speed of the tip of the wing is a little more complex to approximate, but it would be a fairly simple calculation. Actually, there are several relevant speeds: The overall speed of the bird in normal flight, the speed of bird "near hover" as it approaches a flower. The wing beat rate, in cycles per second. The Wing Tip maximum speed. I suppose there would be many other relevant "speed" measures.

What are the steps used when finding the motion?
-To graph the motion of a hummingbird, a very high speed video or film would be most useful. However, a "composite" made from various stills is another very practical method, since we are talking about what is essentially an aggregate measure anyway.

Would you recommend flash photography or high speed photography as a means of finding the speed? If so, because of what reasons?
-Yes. High speed flash is a very easy means to calculate the speed of the wing stroke AT VARIOUS POINTS in the wing stroke. As I said, by measuring the blur of a short exposure directly, you can calculate the speed directly, if you know precisely the duration of the flash. I would recommend using an independent light sensor to make this measurement, since the length of the flash can vary tremendously, depending on exposure. Calibrating this measure would be extremely easy, using a rotating disc of known rpm, for example. The only downside is that flash which is fast enough is not cheap, nor readily available. My dad's fast flash is NOT commercially available, and it's maker is dead. See my web page links for Woods Electronics for a hope for a new maker. There are also "True" high speed flash which are even faster, but these are only suitable for the Fastest part of the wing stroke. If the flash is too brief, you won't be able to see the blur in the photograph. Flashes are adjustable, within limits. However, ambient light must be 2 stops lower than the flash light, as a rule of thumb, and hummingbirds won't fly in the dark.

How can hummingbirds flap their wings, yet stay in the same spot?
-Hummingbird can hover because they "scull" in the air. The motion is a figure 8, and they very the pitch of the wing as it moves along the path. If you think this is easy, then try it yourself in a canoe with a canoe paddle. It can move you slowly in any direction, but it takes a while to get the hang of it. The hummingbird pea-brain knows migration routes, flying, reproduction, rearing eating, and fighting, which is a variant on sex and eating. That's an amazing amount for such a pea-brain, but it's not a whole lot, either.

Links and Resources

Greg Scott's site
Hummingbirds.net
The Hummingbird Website
Operation Ruby Throat