This is bird note.

Hummingbirds make hovering look effortless.

They're built for it, with flexible wrists that rotate their wings in a rapid figure

8 motion, generating almost constant lift.

But wind tunnel experiments with flying birds show that hovering is hard work.

As one scientist put it, a hovering hummingbird represents the upper limit of

aerobic locomotion invertebrates. In other words, hummingbirds are athletes on par with galloping horses or humans running a marathon.

But hummingbirds aren't the only flyers up to the challenge.

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Euressian skylarks even sing while hovering, sometimes for minutes on end.

Different from a hummingbird, a lark flutters its wings 10 to 12 times per second, relying entirely on lift produced by the downstroke.

Other small birds hover briefly.

In search of insects, tiny birds like kinglets float above the tips of branches for just a few seconds.

Even larger birds like hawks and kites make use of head-on breezes and what's called wind hovering when they search the ground for prey.

The kestrel is a master of wing hovering. Flapping forward but counterbalanced by the wind, the

Kestrel appears tethered to the ground by a string.

So while Hummers might be the most impressive hoverers, they're not the only birds to employ

this gravity-defying maneuver.

For Bird Note, I'm Ariana Rimmel.