Did you know? Nature's winter survival strategies

MOLLY MURRAY The News Journal 4:45 p.m. EST January 20, 2015

When it's bitter cold, windy and snow and ice cover the landscape, we can stay indoors, turn up the heat and settle down with a cup of hot cocoa. Or we can bundle up in layers, head outdoors and have a snowball fight.

But how would we fare without polar fleece, wool blankets, grocery stores and heat?

We may complain about how cold it is or how much snow covers the ground but for other animals from birds to bats to bugs, getting through winter is all about food, shelter and survival strategies that make the difference between life and death.

Our winter survivors adapt, find the best habitat and often alter their metabolisms. Some animals like snow geese, monarch butterflies and caribou migrate south for the winter.

Some mammals -- horses, dogs and cats, for instance -- grow in a thick winter coat. Many species even add a layer of fat.

Some slow down their systems, lower their heart rate and breathing and stop eating -- in short, they take a long winter's nap.

Others, like wood frogs, shut down completely and have sugars in their blood that allow them to freeze and then thaw,

And others have developed strategies to find food and shelter even when it is bitter cold.

Even with frogs, said Jim White, with the Delaware Nature Society, "there are different ways that different species survive winter."

Green frogs and bullfrogs, for instance, live in water through the winter so on warm, winter days, they can come out of a state called brumation, he said.

We've all heard of hibernation. But this term typically applies to warm blooded animals like mammals. These animals find a shelter like a den or nest, settle in, slow their heart rate, their breathing and essentially go into an energy-saving slowdown mode. They don't eat, instead, depending on fat reserves to maintain their body temperature and hold their organs in a safe mode.

With cold-blooded animals it's called brumation.

Reptiles, turtles and amphibians are ectotherms meaning they regulate their body temperature by the outside environment. As mammals, we are endotherms. We regulate out body heat internally from the foods we eat and by burning stored fats.

During brumation, bull frogs can become more active as temperatures rise and can slow down again as it chills -- a perfect solution in a place like Delaware where there can be wild winter temperature swings.

Wood frogs and American toads, on the other hand, brumate on land, White said.

"They are just waiting out the winter," and they pretty much don't move around until temperatures are warmer and more stable.

Wood frogs are among the first to appear in Delaware in the late winter and then, temperatures can still swing from above to below freezing, White said. They have sugars in their blood that allow them to freeze solid and then thaw without a problem, he said. These sugars keep crystals from forming. It's the crystals that do the damage in other animals, he said

For reptiles and amphibians, there are two issues in winter, White said. One is temperature and the other is lack of food. The colder these cold-blooded animals get, the less able they are to digest any food they might find.

As for salamanders in Delaware, they hunker down below the frost line and are active all winter in underground habitats, he said.

White said that sometimes in old farmhouses, you can find as many as 10 or 20 snakes living in the basement through the winter.

"We call them hibernaculums," he said.

There are other animals in Delaware that turn to man-made hibernaculums. Little brown bats spend the winter at places like Fort Delaware throughout the coldest part of winter.

In nearby New Jersey, scientists at Rutgers Cooperative Extension believe that little brown bats move into the hibernaculums when temperatures are 39 to 55 degrees.

An interesting thing about these bats is they mate in the fall but the females stockpile the sperm until the following spring when temperature rise and insects are more abundant.

But what about animals in really cold places? Caribou in the Arctic National Wildlife Refuge migrate south for the winter often from the coastal plain to the edge of the Brooks Range mountains on Alaska's North Slope. It's mighty cold in either location. One reason for their seasonal northward migration is to minimize the impact of insects. Females and their young seek places with cooler breezes to keep the bugs away -- something that is possible in the coastal plain.

As for Monarch butterflies, they migrate, too. A late hatch of butterflies from our area and the midwest fly south to a remote mountain region of Mexico for the winter.

"Now, mind you, this is not the day the system evolved - many of these species had ancestors that originated in the tropics or subtropics or somewhere substantially farther south than the boreal zone; these ancestors' patterns saw them move north out of the tropics and subtropics to exploit the seasonal flush of activity in points farther north such as the boreal forest black fly explosion after thaw in the Arctic summer," he said.

Birds like snow geese used to fly south to the Carolinas for the winter but with abundant food sources such as winter wheat, waste corn and soybeans and winters where waterways and marshes aren't frozen as often, these birds stop short in places further north like Delaware's coast marshes.

Non-migrating winter birds like cardinals have feathers, which Farnsworth said "provide exceptional warmth for birds. Their structures and interconnections allow for a literal cover beneath which birds can insulate themselves."

The means for many species cold, at least to a certain point, is less of an issue than the availability of food, he said.

Then there are those insects like the invasive Brown marmorated stink bug and the Asian lady beetle. In their native habitats, said University of Delaware entomologist and cooperative extension specialist Brian Kunkel, they would find nooks and crannies in rocks and tree bark as shelter from the cold. They do the same here in Delaware but they also find shelter in your house or your shed.

Often you might have many of these insects over wintering in your attic. They aren't feeding or reproducing. Instead, they are just staying warm enough to survive winter. But on warm days, they perk up and take a look around, which is why you may see them in your living areas, he said.

Japanese Beetles, on the other hand, survive winter in the white grub stage and they live beneath the ground, he said.

Other insects survive as eggs or larvae, he said.

While the air temperature is highly variable during the winter, underground and in the water are more consistant so seeking those areas is a survival strategy for some insects, he said.

"Any protection from the extremes," Kunkel said.

Animals that are active all winter can still find food and shelter.

White tail deer seek shelter from the cold and wind by finding a protected, wooded area to bed down. Deer have sharp, narrow hoofs and can cut through the snow to find food such as fallen acorns. They can also reach up to pull bark, leaves and branches from tree. Females, which are typically bred in the fall in Delaware, will give birth in the spring. Deer develop a thicker, winter coat.

Red and Gray Fox stay in dens when weather gets bad. They curl up in a ball and wrap their thick tail around their body like a sweater. Their fur provides insulation when it snows.

Eastern Cottontail Rabbit create shallow patch in the ground for warmth. This area is usually within a thicket or hedgerow to block the wind. rabbits can dig through the snow to find food.

Gray Squirrels stockpiled nuts all fall and in the winter they depend on these caches when they den up during extreme cold or bad weather.

Weasels curl into a ball to stay warm. Their coats turn white except in the southern part of their range.

Opossum den up when the weather is cold or stormy but this behavior only lasts a day or two.

Raccoon have a heavy winter coat to keep them warm. They mate in late winter.

Beaver, Muskrat, Mink and River Otter spend their time in and near water and have thick coats to keep them warm. They give birth to young in the spring.

Several species of birds are year-round residents of Delaware but one of the most striking when it snows is the American cardinal. Blue Jays, on the other hand, move short distances in the winter.

Animals that hiberate, bromate or slow their body functions

Eastern Chipmunk - Does not hibernate, but goes through a period of inactivity called torpor. Will occasionally awaken to eat food from its food cache.

Black Bear - Delaware's last known black bear was extirpated in the 1930s in the Great Cypress Swamp of Sussex County. But there are black bears in neighboring Maryland, Pennsylvania and New Jersey. These animals go into a winter resting state called "denning". It's not really hibernation because they can wake up and go outside if there is a warm spell. Once it turns cold, they head back to the den. Female black bears give birth in this dormant state.

Meadow Jumping Mouse - True hibernator, stays in a sleep until early spring

Little Brown Bats - Hibernate throughout the winter when there are limited insect sources of food.

Groundhog - Hibernation in the coldest part of winter, typically from December to early February in our region. In the wild, they don't necessarily emerge on Feb. 2, Groundhog Day!

Water frogs such as Bull frogs -- Bromulate in ponds but can "wakeup" if the weather warms.

Ground frogs and toads -- Bromulate on land. Don't typically emerge until the weather warms in late winter and spring.

Salamanders and snakes -- Spend the winter underground or in shelters where temperatures are about 50-degrees.

Animals that migrate

Canada and snow geese -- migrate south from Arctic breeding grounds. They often follow food supplies and some stay in our region year-round and never migrate back to the Arctic to breed.

Monarch Butterflies -- In our area and the Central U.S., they migrate to Mexico for the winter. On the Pacific coast, they migrate to Pacific Grove, California.

Caribou in the Arctic National Wildlife Refuge spend the spring and summer on the northern Alaska coast plan, where cooler breezes keep insects away. They spend winter to the south along the Brooks Range of the North Slope.

Many other bird species from hawks to warblers to osprey migrate south for the winter.

Sources: University of Delaware Cooperative Extension; Rutgers Cooperative Extension; Cornell Lab of Ornithology; Maryland Department of Natural Resources; Delaware Nature Society.

Contact Molly Murray at (302) 463-3334 or mmurray@delawareonline.com