Why Hummingbirds Hum

Some of my favorite things about summer are the sounds. I love the dawn chorus of birds in the morning and their calls to each other throughout the day. Crickets, grasshoppers, cicadas, and other bugs chirp, click, trill, and rattle. Frogs peep. And hummingbirds hum. In my yard, the sound of hummingbirds whizzing through the air has been constant this year.

UC Botanical Garden, Berkeley, California

But why do they make that noise? It’s not a purposeful call or song. Instead, it’s the sound of their wingbeats, roughly 70 strokes per second. More specifically, the upstroke of the birds’ wingbeats creates the sound.

This discovery was made by curious researchers at Standford using high-speed cameras, hundreds of microphones (2,176 to be exact), and some Anna’s hummingbirds. The technology created a 3D sound map of the wingbeats. What they found is that hummingbirds’ wings create lift on both the upper and downstroke of their wings, unlike other birds who create lift only with the downstroke. Further, the speed of hummingbird wingbeats, and the differences created in air pressure, make the humming sound. Different hummingbirds generate different sounds as a result of how air moves over their feathers and the shape of their wings.

It amazes me that the tiny wings on those tiny birds can fill the air with a summer song. I am going to savor that for a few more weeks…