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How Do Hardworking Hummingbirds Keep Cool?

Special “windows” in the feathers covering their tiny bodies prevent overheating while hovering and flying

(Graeme Guy/ BIA/Minden Pictures/Corbis)
smithsonian.com

Hummingbirds are extreme flying machines. The tiny, superbly athletic birds can stay steady even in 20-mile-per-hour wind and can make abrupt dives by beating their wings between 70 and 200 times per second. That speed and agility requires some very active muscles, so experts have wondered how exactly the feathered birds keep cool while working so hard.

As it turns out, the jewel-colored birds have patches on their bodies where feathers are thin to non-existent, and they rely on them for heat dissipation, reports Claire Asher for Science.

By dangling their toes and legs in the air as they hover rather than tucking them in during flight like other birds, hummingbirds release some of the excess heat they generate. Hot spots on their feet, along with regions under their wings and around their eyes where feathers are thinner, can get up to 8 degrees Celsius warmer than the rest of their bodies, a research team reports in Royal Society Open Science. These are the places where the birds are shedding excess heat.

Reuters video produced by Christine Nguyen (via Tech Insider) shows what the feather windows look like on hummingbirds. The patches that release heat around their eyes and wings appear bright white through the lens of an infrared camera.

At speeds of zero feet per second (hovering) up to a darting 39 feet per second, the birds lost enough heat through these windows to keep their overall body temperatures within a safe range, the researchers report.

Hummingbirds’ small size also makes them vulnerable to heat loss. During cold snaps, the tiny birds can ramp down their metabolism, heartbeats and breathing rates to enter a state of torpor. They also migrate with the seasons, with some species traveling as much as 4,000 miles to reach warmer breeding grounds.

The heat windows, torpor and long migrations together help hummingbirds bear out temperature swings. Those strategies, along with other notable oddities such as reverberating feathers that make music and tongues that work like pumps, ensure that hummingbirds will fascinate with their biology as well as their charming looks.

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