Unique techniques help animals 'survive' through winter

Burrowing in the ground, hibernating and breathing underwater, or huddling together to keep warm. are some surprising "strategies" that help animals survive the cold winter.

While we can simply put on extra sweaters or crank up the air conditioning to 'warm up' through the winter, wildlife has its own ways of getting through the cold months.

Here are some unique 'techniques':

Spider burrows in soil

Many ground-dwelling spiders in North America, such as wolf spiders, overwinter by burrowing in the soil, under leaf litter, or inside logs.

'The temperature difference between the frozen snow surface and just a few inches below the cover is often surprising,' says ecologist George Uetz, a spider expert at the University of Cincinnati in Ohio.

"Many spiders and insects thrive in this 'sub-freezing' environment, or sometimes a few degrees above freezing."

Because spiders are poikilothermic and don't produce body heat, their metabolism slows down as temperatures drop. ' That said, it's not uncommon to see spiders and insects active on warm days,' says Uetz.

Many spiders 'weave' their egg sacs with multiple layers of silk insulation to protect their eggs during the winter. For example, the black and yellow garden spider hatches its eggs in the fall, so the young spiders gather in the egg sacs over winter to emerge en masse in the spring.

Some spiders also have a 'secret weapon': On cool autumn nights, they produce special antifreeze-like compounds to prevent ice crystals from forming inside their bodies, Uetz says . This is a useful 'trick' to survive until spring without freezing.

Turtles hibernate and breathe underwater

Turtles are slow in all seasons, and as winter approaches, they really slow down.

Some species, like the eastern box turtle, simply burrow underground, withdraw into their shells, and enter a state of inactivity—known as hibernation. They survive by burning stored fat.

Painted turtles spend the winter 'dwelling' at the bottom of water , which helps them stay cool even when the surface freezes. Since the body temperature of these poikilotherms matches the temperature of the surrounding water, the cold is not an issue.

Normally, these reptiles breathe air, but in winter they have evolved the ability to absorb oxygen from water and release carbon dioxide into it.

"When poikilotherms get cold, they don't need as much O2, so what they can get from water is usually enough to get them through the winter," says Jackie Litzgus, a biologist at Laurentian University in Ontario.

Turtles exchange gases through 'specialized' blood vessels near the surface of their skin, the lining of their mouths, and even the cloaca - a cavity that serves as both a waste disposal site and a reproductive opening.

When oxygen becomes extremely scarce, painted and snapping turtles can even switch to a metabolism that does not require oxygen. Respiration in this way creates a dangerous buildup of lactic acid, but turtles can eat calcium from their shells to neutralize the acid buildup.

Honey bees swarm and 'generate heat'

When it gets colder, they squish inward, improving insulation. (Source: National Geographic).

As temperatures drop, European honey bees fly back to their hives, huddle together and stay active throughout the long winter months.

"This is very unique, no other insect can get through the winter by keeping its body warm," said Thomas Seeley, a biologist at Cornell University.

Worker bees gather around the queen, adjusting the composition of the 'hive' to match the temperature changes. Bees generate heat by simultaneously contracting and relaxing two sets of muscles used to move their wings during flight.

'The energy they expend isn't moving or doing anything other than generating heat,' Seely explains .

The queen's nest in the middle of the hive is the warmest and most comfortable, but even the bees on the outside don't freeze. As it gets colder, they squeeze inward, improving their insulation and compressing the area that needs to be kept warm.

'The bees in the dense outer layer are meant to keep the temperature above 50 degrees F [10 degrees C]'. That helps them survive,' Seely said.

This 'strategy' depends on months of 'planning'. During the flower-rich summer months, bees produce and store 90 pounds (more than 40kg) of honey to sustain the hive through the winter. They also choose their location wisely, aiming for the top of a hollow tree, to create a warm environment.

Squirrels 'build' shelters

Chipmunks are members of the squirrel family, but unlike their bushy-tailed relatives, you won't see them out and about all winter. Nor do they hibernate all season, like groundhogs do before emerging to signal the arrival of spring.

Instead, these small mammals live in complex systems of burrows, tunnels and 'chambers' that they 'build' to connect small holes filled with nuts, seeds and other stored food.

The eastern chipmunk burrows near rotten logs or piles of rocks, carving a tunnel that leads to its "rooms," including its "toilet." (Source: Shutterstock/National Geographic) 

Eastern chipmunks spend days in hibernation, during which their heart rate drops from about 350 beats to the 'single digits,' and their body temperature drops from 94 degrees F (34 degrees C) to the ambient temperature of their burrows - as low as 40 degrees F (just over 4 degrees C). But they wake up every few days to eat and use certain 'toilet stalls.'

Snowbirds fly to warmer climates

According to Jill Deppe, director of the National Audubon Society's Migratory Bird Initiative, more than 70% of backyard birds in the United States and Canada are migratory, and many fly south for the winter.

'So even if they don't necessarily know what kind of birds they are, people notice that in the fall, their backyards become quieter.'

Audubon's Bird Migration Explorer maps the annual flights of more than 450 species of birds migrating to warmer climes - and some are ' very cryptic'.

These red-necked hummingbirds weigh only as much as a penny, but on their way to Central America, some of them have to fly across the Gulf of Mexico – up to 500 miles (805km) – in just one day.

'They're so light, they seem to ride the wind,' says Deppe. Meanwhile, some species of rufous hummingbirds in the western United States 'break the pattern of flying south'.

'Some birds will fly to places you don't expect,' says Deppe. ' There are quite a few that actually fly east, so you'll see them in your backyard in Louisiana or Florida in the winter.'

'If it's getting cold where you live, raise a glass to the resilient animals that can make it through the harshest of seasons' .