How can hummingbirds fly upside-down and backwards?
How can hummingbirds fly upside-down and backwards? asks a reader.
Hummingbirds use enormous amounts of energy simply being themselves. When a hummingbird is sitting quietly on a branch, its heart beats a staccato 550 times a minute. When a bird is engaged in aerial acrobatics, its heart can speed up to 1,200 beats a minute. A person whose body burned energy at the rate of a hummingbird would have to eat about 155,000 calories a day. In fast food, that’s the equivalent of about 287 Big Macs.
But hummingbirds prefer nectar to burgers. So instead of hovering at the nearest drive-through window, a hummingbird helicopters alongside a flower.
Just as a helicopter can perform feats that put ordinary planes to shame, so hummingbirds can fly rings around other birds — including upside down and backwards (although not in heels).
Most birds fly by flapping, moving their wings forward and downward with great force. A bird’s flight muscles are specialized chest muscles (pectorals), souped-up versions of human pecs. The average bird’s “upstroke” muscles are weak, weighing only 5 to 10 percent as much as its powerful downstroke muscles. But hummingbirds are built for acrobatics. A hummingbird’s pecs make up nearly a third of its body weight, compared to 15 to 20 percent for other birds. (Imagine a 180-lb. body-builder — with 60-lb. pecs). And a hummingbird’s upstroke muscles are as big and powerful as its downstrokes.
Like a regular bird, a hummingbird flaps his or her wings to fly forward. But a hummingbird’s wings rotate at its flexible shoulders nearly 180 degrees. Meanwhile, the tiny bird’s wings beat about 18 to 80 times a second. (Compare that to a vulture’s once-a-second flap.)
By slanting the angle of its wings and using its powerful chest muscles, a hummingbird can tip up and fly backwards. And by spreading its tail and doing a quick backward somersault, a hummingbird can also fly upside down (a position in which its improved upstroke — now a downstroke — becomes important). Finally, a hummingbird can hover. It does so tilting its body nearly straight up and down, while moving its wings forward and backward in a figure-eight. In addition, like a helicopter, a hummingbird can lift straight up into the air.
Recent studies have revealed that hummingbirds combine a bird’s body with the flying tricks of insects, like the hover-and-dart motions of dragonflies. Researchers used microscopic droplets of olive oil, tiny enough to float and move in air. With a laser lighting the droplets, the researchers used an ultra-fast camera to capture the air patterns left in a hovering hummingbird’s wake.
Insects have nearly flat wings, and use a figure-eight wing pattern that creates nearly equal lift during downstrokes and upstrokes. Bird wings are more like human arms than insect wings. And a hummingbird is no match for an insect, since about 75 percent of its weight support, according to the researchers, comes from the downstroke. But other birds’ in-flight weight support comes almost 100 percent from the downstroke. The 25 percent lift on the upstroke gives hummingbirds their insect-like hovering advantage.
