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The deep freeze gripping the nation earlier this week has finally loosened its hold, after breaking records from Minnesota to Florida. While we humans took refuge inside from the extreme cold, the creatures that inhabit the outside world were left to their own defenses.

Bears, bats, frogs, and other hibernators may not have been disturbed, but it was a different story for animals that stay active throughout the winter. “The extreme cold places additional stress on them,” says John Organ, chief of the U.S. Fish and Wildlife Service’s Northeast Region Division of Wildlife and Sport Fish Restoration. “They are burning more energy, which makes them susceptible to starvation and predation.”

The lack of snow cover in the Northeast likely put some creatures at a disadvantage, says Organ. Coyotes, for example, probably had to expend more energy finding food, since the snow wasn’t deep enough for good deer hunting. “Chasing them down isn’t as easy as when you have deep snow and a crust that deer punch through and coyotes can walk atop,” he says. Meanwhile, when the mercury drops, ruffed grouse normally bury themselves in the snow for insulation, and as protection from predators. “But again, we don’t have deep snow, so the combination of a deep freeze and limited snow can be a double whammy.” 

"On a positive note," Organ adds, "the extreme cold can serve to such as the hemlock woolly adelgid."

In general, birds that winter in the north are pretty well adapted to even extreme events like the one this week, says Bob Russell, a wetland bird biologist in the USFWS’s Minneapolis regional office. (Click here for “How Birds Cope With Cold in Winter.”) Some species will head south to escape the frigid temps. Northern harriers, for example, typically retreat south until they pass the snow line, he says. And waterfowl simply take to the wing when ponds and lakes freeze up. “Already this year hundreds of scoters [three species of sea duck] have been seen off the Florida coast in numbers not seen before,” says Russell.

Death is a real risk for those that stay. “Some mortality is likely to occur with weaker members of various species,” says Russell, “a culling effect to weed out the less hardy.

Russell suspects that northerly populations of northern cardinals might suffer some from the cold. American robins and cedar waxwings—overwintering in northern Illinois, Minnesota, and Wisconsin in impressive numbers because of a large fruit crop—are mobile and will likely survive as long as they can find food.

Less hardy birds, including eastern bluebirds, brown creepers, and kinglets, might suffer the most. “Some of them were lured into staying north of their usual haunts by mild November weather, and now with increasing daylight are not apt to move south, but tough it out in situ, with some losses to the cold likely,” says Russell. Other species, like northern saw-whet owls, unable to find rodents beneath iced-over snow, might starve.

In New Jersey’s Hunterdon County, the odd behavior of a downy woodpecker puzzled USFWS biologist Colin Osborn. The normally dynamic bird was resting motionless against the trunk of a sizeable red oak. “After going outside later though, I realized what this chilly little bird was doing,” says Osborn. “It was on the leeward side of the tree using the large trunk to shield itself from the strong and bitter cold wind.”

Duck researchers are keeping a close eye on the birds they’re tracking, since some species, including black ducks, hunker down in the extreme cold rather than fly away. “Tracked birds have been known to freeze,” says Patrick Devers, a scientist with the , an international conservation partnership dedicated to conserving the species. 

Chris Dwyer, acting chief of migratory birds for the USFWS’s Northeast Region, agrees that there’s mounting evidence that black ducks start dying off during severe winter weather.

He’s keeping tabs on what the weather might mean for long-tailed ducks in the Great Lakes as water bodies freeze up. “In the past we’ve heard similar reports from locals within the Great Lakes region that long-tailed ducks also hunker down and end up freezing as the ice closes and they no longer have access to food,” says Dwyer. “We've always thought the logical thing would be for these birds to pick up and move further south, but satellite transmitters have opened up a new window in our understanding of how reasonable that assumption may be.”

Dwyer points out that sea ducks along the coast also seem to stay put. “But as long as they continue to have access to food,” he says, “they do just fine.”

As counterintuitive as it may seem, we might actually experience more deep freezes, even as the planet continues to warm.

Climate Central :

The weather pattern driving the extreme cold into the U.S.—with a weaker moving around the Arctic like a slowing spinning top, eventually falling over and blowing open the door to the Arctic freezer—fits with other recently observed instances of unusual fall and wintertime jet stream configurations. Such weather patterns, which can feature relatively mild conditions in the Arctic at the same time dangerously cold conditions exist in vast parts of the lower 48, may be tied to the in the Arctic due, in part, to manmade climate change.

It's a chilly forecast, especially for species like black ducks.