The streets remain quiet in several cities across the Midwest as the polar vortex continues to grip the region. Subzero temperatures and blizzard-like conditions convinced many residents to stay indoors rather than brave the storm.
But humans aren't the only ones taking cover.
Birds are also noticeably absent from the sky — and with record-breaking windchills, it's not surprising. On Wednesday, Chicago dropped to a low of around minus 23, slightly above the city's lowest-ever reading of minus 27 from January 1985. Milwaukee had similar conditions. Minneapolis recorded minus 27. Sioux Falls, South Dakota, saw minus 25.
While residents stay bundled inside, many can't help but wonder: What happens to the local birds?
Some feathered creatures are better equipped to take on the cold than others. Snowy owls, for example, are from the Arctic and can reportedly withstand temperatures as low as minus 40. Other birds that are used to spending the season in cities with harsher winters, such as Chicago or Minneapolis, are also adaptable in fluctuating weather.
“Species that spend the winter regularly in the region have evolved lots of different ways to deal with these cold snaps,” John Bates, associate curator of birds at the Field Museum of Natural History in Chicago, told Atlas Obscura on Wednesday.
Unlike humans, birds are built to survive freezing temperatures for longer periods of time.
Their feet and legs are "ingeniously designed" so they're basically numb already, according to the Mother Nature Network, which explains there's a group of arteries that essentially "wires" a bird's feet to its heart.
“Unlike humans, they have counter-current blood circulation in their legs, which allows heat to be transferred from warm arteries to cool veins and keep their legs from freezing,” Alexandra Anderson, a graduate student in environmental and life sciences at Trent University, told Atlas Obscura.
The fact their feet don't have any muscle or nerve tissue helps doesn't hurt. They maintain their 105-degree body temperature by fluffing their feathers, "thickening the insulation around their bodies," the Cornell Lab of Ornithology explained in a recent blog post.
However, the best tactic of birds when it comes to surviving freezing temperatures: preparation.
They "maximize calories ingested while minimizing calories spent," the Cornell Lab of Ornithology added.
Every type of bird may have slightly different ways of going about this, but their goal is the same — stock up on food and avoid movement in severe weather. Some birds, like chickadees, woodpeckers, jays and crows, store seeds in tiny crevices or hit up bird feeders, while other primarily insect-eating birds simply peck the ground or trees when they're hungry.
If they aren't thoroughly prepared for extreme temperatures — such as a polar vortex — they could run into problems, though. They need to "bump up" their metabolism to help keep their bodies warm.
"This uses much more energy than normal, which will mean the bird will need to eat more to stay alive,” Anderson says. “Eventually, if the body cannot generate enough heat, the birds will become hypothermic and likely die.”
But the chances of that happening are slim (hopefully) since the temperatures are expected to start rising again in the coming days, giving birds an opportunity to feast freely again.
A meteorologist says parts of the northern U.S. are going to experience an “unprecedented” and “dramatic warm-up.”
Weather Underground’s meteorology director Jeff Masters says places in Michigan and Illinois experiencing record or near-record cold this week are expected to be around 50 degrees by Monday.
The Associated Press contributed to this report.