How Does Extreme Winter Weather Affect Wildlife?

Carolina Wren

While visiting my parents and brother in central Pennsylvania over the holidays, I enjoyed watching the antics of the Carolina wrens visiting their bird feeders. They’re fun birds to observe, always active and vocal.

They’re also somewhat unfamiliar to me: growing up, we’d never see them around the yard. Indeed, Carolina wrens have been expanding their range north over the past decades. They are not migrants: they live in a locale year round.

However, these birds don’t fare well during periods of very cold weather. Since they don’t migrate, they often perish.

This pattern has been recorded by the Great Backyard Bird Count, a citizen science initiative held each February where participants keep track of birds seen in backyards or nearby parks. In years with very cold weather, Carolina wren sightings diminish greatly — the birds have died off, and their range contracts.

The Carolina wren population eventually expands northwards again. It takes time. According to Great Backyard Bird Count reports, it can be ten years or more until Carolina wrens return to northern states in numbers following a cold weather die-off.

My parents tell me they have not seen the Carolina wrens this week, not a promising sign. The polar vortex will likely wipe out many of these birds in the East and Midwest. They’ll be back, but not immediately.

Virginia Opossum

The opossum has been expanding its range north for decades. It’s particularly well adapted to humanity, able to survive amidst farms, city parks and suburbs.

It’s much less well adapted to winter weather.

Unlike some other mid-sized mammals that thrive in the presence of humans – think raccoons, red foxes, coyotes – opossums don’t have furry, protective tails. In fact, their tails (and ears) are hairless, making them particularly susceptible to frostbite and even hypothermia.

Many opossums bear physical evidence of  surviving harsh winters – damaged ears and tails. Their tails often appear stumpy or as if something had bitten them off, but these are signs that their tails suffered frostbite.

Opossums will den for a few days to escape the cold, but they don’t hibernate. They have to feed periodically. Sometimes they’ll change their nocturnal habits and feed in daylight hours during the winter, to take advantage of warmer temperatures.

That doesn’t make much difference, though, when it’s -20 degrees Fahrenheit (as it was in parts of their range this week).

Expect to see a lot of tail-challenged opossums this spring.

Bobwhite Quail

The northern bobwhite can survive harsh winters quite well – provided it has ample habitat.

This quail species was once a common farmland and grassland bird, and a celebrated game species over much of its range. Since 1966, its populations have declined by 85 percent. While the reasons for this decline remain contested, nearly all biologists agree that habitat loss plays a major factor.

Thick cover along fields provides many benefits for quail, among them protection from inclement weather. Bobwhites, like many species, need to burn more energy to stay warm in winter. Even a few degrees temperature can have a tremendous impact on survival. The conservation group Quail Forever has found that “the temperature inside a high-quality shelterbelt – ideal cover from the cold – can be 5°F warmer.”

Those 5 degrees can be the difference between life and death. Recent research found that a severe winter weather event can have long-lasting impacts on northern bobwhite populations. A healthy quail population could bounce back from this decline, but a population in peril – with inadequate habitat – may take years to recover, if it ever does.

Manatee

Perhaps hardest hit are animals like manatees that thrive in more tropical environments, but encounter chilly weather in the northern parts of their range. Florida, home to well-known populations of manatees, is also experiencing a cold spell this week.

Manatees require water 68 degrees or warmer. Despite looking rather plump, they  have very little fat to protect them in cold water.

When they swim in cold water for long periods, they suffer from what is known as manatee cold stress syndrome – leading to starvation and death.

There are current reports of hundreds of manatees moving into warmer springs that remain a constant temperature.   Fortunately, these springs are being closed to public access so the manatees can take refuge there without being further stressed by people.

These winter warm-water areas are vital to the continued survival of manatees in Florida.

New England Cottontail

The New England cottontail has faced numerous challenges to its survival – lack of young forest habitat, invasive plant species and competition from introduced eastern cottontails (a similar but separate species). And yet conservation efforts, including improved forest management and captive breeding, offer hope.

Will a harsh winter harm these “Yankee cottontails”? It would seem that a rabbit that lives in New England would be well suited to winter. And that’s probably often the case. With excellent habitat and a thriving population, the rabbits would likely do just fine. But a population on the brink without access to food may be wiped out by a heavy and persistent snow.

Researchers in 2015 found a 60 percent reduction in New England cottontail sites in Maine following a harsh winter. Every radio-collared rabbit in New Hampshire perished in that same winter. Plants like blackberry and raspberry bushes become buried with snow, making it harder for the rabbits to feed. The brown rabbits may also stick out more for predators (unlike snowshoe hares which turn white).

Non-Native Reptiles

In Florida, species like Burmese pythons and green iguanas can become invasive, posing serious threats to native wildlife. When these species are released into a new environment, they find lots of prey but none of their native predators. Their populations can grow rapidly.

Still, they’re not equipped for cold weather. Most conservationists consider this a good thing.

During the so-called “deep freeze” Florida experienced in 2010, there were frequent sensational media stories of iguanas dropping from trees.  Most of these iguanas weren’t actually dead; they enter a catatonic state when the temperature drops to 37 degrees Fahrenheit.

There were similar stories of pythons dying by the thousands, although this may have been overstated – there are still plenty of non-native snakes in South Florida.

Zoologist Vladimir Dinets reports in his new book Dragon Songs that non-native spectacled caimans (a crocodilian species) pretty much disappeared from the state following the freeze.

It’s interesting to note that native alligators did just fine. But Dinets reports that dozens of American crocodiles, a native species, died due to the cold in 2010.

Forest Pests

Frigid temperatures might have another positive effect: killing invasive forest pests. These non-native pests can hammer forests but cold weather offers some hope of slowing the spread.

As Minnesota Public Radio reports, the emerald ash borer could suffer through the kill of a high percentage of emerald ash borer larvae. Since it was first confirmed in southern Michigan in 2002, the emerald ash borer has spread rapidly — now infesting more than 100,000 square miles. It devastates ash trees, and there’s no hope of eradication. But at least the cold weather might slow the spread, buying conservationists more time.

The Don’t Move Firewood blog also reports that the hemlock woolly adelgid, an insect devastating to eastern forests, is affected by cold weather. However, the  temperature needs to drop below -22 degrees Fahrenheit before this pest begins dying in numbers.

Leigh Greenwood of Don’t Move Firewood notes that even the coldest weather won’t kill all forest pests, it will merely reduce their numbers. So please don’t move firewood to new locations; there may still be (living) invasive species lurking there, and you could spread the pests to new locations.

It will be interesting to learn what effects the “polar vortex” has on native and non-native wildlife. Are you seeing any impacts on wild creatures near your home? Your observations can help scientists learn more about how species fare in this cold weather.

Ruffed Grouse

Ruffed grouse thrive in winter and heavy snows and frigid temperatures will be unlikely to affect populations. But a sudden shift in temperatures might trap some grouse…under the snow.

As is the case with skiers, ruffed grouse love powder. When the snow is fluffy, this bird creates one of winter’s most unusual wildlife shelters.

Forget moving out of the snow; ruffed grouse plunge into it.

The ruffed grouse flies along and dive bombs head first into deep, fluffy snow – completely submerging itself. Its body heat then creates a sealed dome under the snow: essentially, its own igloo.

This structure allows the grouse to stay warm even in the most inclement conditions. Research shows that the snow shelter can warm to 32 degrees Fahrenheit, and rarely drops below 20 degrees — even when it’s much colder outside.

The ruffed grouse is found in many forested areas of North America, so it’s the grouse you’re most likely to see on winter wanderings.

In fact, numerous stories exist of grouse “exploding” out of the snow when a skier or snowshoer approaches – surely a dramatic sight, and one I always hope to see on my own winter outings. However, I’ve never seen a firsthand report, so it’s unclear how often this really happens.

Unfortunately, a snow shelter is not without risks for ruffed grouse. Researchers have found instances when a crust forms on the snow, trapping the grouse inside. If the crust lasts too long, the grouse is unable to escape and dies.