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Brumation and torpor: How animals survive cold snaps by playing dead-ish

A stunned iguana lies on the sidewalk after having fallen from a tree on Jan. 6, 2010, in Surfside, Fla. Very cold temperatures can stun the invasive reptiles into a state called brumation. But the iguanas won't necessarily die.
Wilfredo Lee
A stunned iguana lies on the sidewalk after having fallen from a tree on Jan. 6, 2010, in Surfside, Fla. Very cold temperatures can stun the invasive reptiles into a state called brumation. But the iguanas won't necessarily die.

While people in the Northeast are the ones bearing the brunt of another snowstorm, the rest of the country is still experiencing winter weather. Parts of the Pacific Northwest and Northwest are receiving their own dose of rain and snow this week. And Floridians are experiencing low temperatures in the 30s in some areas, after getting an icy blast in January.

Humans can make do with scarves, coats and gloves in cold weather. But animals need to use their innate abilities to cope.

While rodents and some other animals hibernate for the winter, reptiles and birds do something similar but a little different.

Reptiles go into brumation

In Texas, where the city of Beaumont reached a low of 18 degrees Fahrenheit last month, alligators were seen frozen — yet alive! — in iced-over water. By ensuring their snouts stayed above the water line, the coldblooded creatures were able to lower their body temperatures to survive the cold snap.

The process, in the case of coldblooded animals like reptiles, is called brumation — it's like a temporary version of a mammal hibernating. While in this state, reptiles become lethargic and they can go for long stretches without eating or drinking. Alligators, bearded dragons, and turtles can be in brumation from just a few hours to months.

On the occasions when temperatures plummet into the 30s of 40s in Florida, residents are warned to watch out for falling iguanas. When it gets cold, the lizards fall into a deep slumber, during which they can lose their grip when they're up in trees. That can spell trouble for people walking below and it can be especially dangerous for smaller iguanas.

"Generally speaking, the larger the iguana, the more it survives without showing any type of lasting effects. The smaller ones, however — you know, when you get the 2-footers and smaller — those animals many times do not recover," Ron Magill of Zoo Miami told NPR after a particularly chilly winter storm in 2018.

The sight and thud of the raining iguanas, which often land legs-up, can sometimes startle Floridians. Several captured the motionless animals in photos and on video across social media, marveling when they appeared to reanimate and walk off as soon as temperatures warmed.

But as NPR reported in 2018, one man got an even greater surprise after he'd picked up a mess of iguanas and loaded them into his car. (Mess is the term for a group of iguanas.) He'd hoped to take them home and eat them. Instead, Magill said, "when they went back into the vehicle, the vehicle warmed up, and those iguanas started coming back to life. And all of a sudden, they started getting up and running around in the car, and it caused an accident."

Birds go into a state called torpor

An Anna's hummingbird is pictured. Recent winter storms in Oregon and British Columbia have been sending Anna's hummingbirds into a popsicle-like state.
USFWS Pacific Southwest Region / Flickr Creative Commons
Flickr Creative Commons
An Anna's hummingbird is pictured. Recent winter storms in Oregon and British Columbia have been sending Anna's hummingbirds into a popsicle-like state.

Like reptiles and mammals, avians can go into a state called torpor in order to conserve energy under frigid conditions.

"Torpor is somewhere between a power nap and hibernation," said Justin Baldwin, a Ph.D. candidate in biology at Washington University in St. Louis and a co-author of a 2023 study about hummingbirds published in Proceedings of the Royal Society B.

Baldwin studied 29 species of hummingbirds living in the mid- to high-altitude mountains of Colombia. He and other scientists collected various data related to the tiny birds' torpor while in the wild. Researchers found that hummingbirds can enter into deep or shallow torpor, depending on several factors, including their size and weather conditions. Similarly, some can remain in torpor for just a few hours or an entire night. And how quickly they regain their full movement can also vary.

In Oregon and British Columbia, winter storms have been sending Anna's hummingbirds into a popsicle-like state, and that in turn has sent bird-loving residents into a bit of a panic in recent winters.

That's because cold snaps can prove fatal for the tiny birds found along the West Coast, which weigh about 4 grams, have a resting heart rate between 420 to 460 beats per minute and an average body temperature of 107 degrees Fahrenheit. By going into torpor, they can dip their heart rate to about 50 beats per minute and their temperature as low as 48 degrees.

Ted Stannard told the Salish Current in 2022 that he found a seemingly passed out Anna's hummingbird in his Bellingham, Wash., backyard. He could see that although the bird was unresponsive, it was still breathing, so he placed it in a box and took it into his home. He hoped the cozy indoor temps would help it spring back into action.

"He was thoroughly conked out and I let him sleep," Stannard said. "I thought maybe he would wake up and just sit there," he told the newspaper.

It took a few hours but eventually that's exactly what happened, he recounted.

Tips for those with bird feeders

The Bird Alliance of Oregon offers a few tipson how to keep the colorful hummingbirds from having their tongues or other body parts freeze against iced over water in feeders. That starts with ensuring the device has no leaks.

The organization also suggests moving feeders out of the path of direct cold winds and exposure to snow, sleet and ice. Another option is to bring the devices indoors overnight so that the sweet water mixture doesn't freeze.

The human-made nectar that provides food for the hummingbirds — four parts water to one part white sugar — can also be kept from freezing with the use of a feeder warmer, or by wrapping cloth, bubble wrap or holiday lights around it.

"But please be careful to never leave anything dangling or sticky that the birds could get tangled or caught in," the group warns.

If a hummingbird is already stuck, the Wildlife Rescue Association of British Columbia suggests drizzling tepid water on the part of the bird that's stuck to the feeder, then waiting for the bird to pull itself away from the surface.

In cases where the the bird's tongue remains stuck even after the application of tepid water, then it's best to "move the bird and feeder to a warm indoor location to let the surface thaw as quickly as possible."

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Vanessa Romo is a reporter for NPR's News Desk. She covers breaking news on a wide range of topics, weighing in daily on everything from immigration and the treatment of migrant children, to a war-crimes trial where a witness claimed he was the actual killer, to an alleged sex cult. She has also covered the occasional cat-clinging-to-the-hood-of-a-car story.
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