Emperor penguins live in large groups on frozen sea ice in Antarctica. There, winter temperatures can drop to -58° Fahrenheit (-50° Celsius). That’s really cold—even for a penguin! To keep warm, the animals often huddle up. As many as 5,000 penguins can crowd together and stand that way for several hours. The birds take turns standing in the center, where they can keep their body temperature warmer.

Other birds and mammals huddle together to stay warm in the winter too. The strategy works because their bodies produce heat, explains biologist Terrie Williams. Heat escapes through the skin and breath, she says. When animals huddle up, the body heat released by each animal warms others nearby. Standing close together also leaves animals less exposed to the cold air, reducing heat loss.

Emperor penguins live in Antarctica. They form large groups on frozen sea ice. Temperatures can drop to -58° Fahrenheit (-50° Celsius) in the winter. That’s really cold—even for a penguin. The animals often huddle to keep warm! As many as 5,000 penguins can crowd together. They stand that way for several hours. The birds take turns in the center. That’s where they can stay the warmest.

Other birds and mammals huddle up to stay warm in the winter too. This works because their bodies produce heat, says biologist Terrie Williams. Heat escapes through the skin and breath, she says. The body heat given off by each animal warms others nearby. Standing close also leaves animals less open to the cold air. That means their bodies lose less heat.

When winter arrives, many animals build up extra layers of fat. Fat can be burned for energy when food is hard to find. But it has another important purpose—it keeps animals warm!

Good insulation is extra important for mammals like whales and seals that spend their lives in icy waters. “Heat moves through water much faster than air,” explains biologist Dominic McCafferty. That means that animals living in the ocean can lose heat quicker than animals that live on land.

That’s why whales and seals have a special layer of fat called blubber just beneath their skin. This fat keeps them cozy even in frigid water, and it gets thicker in wintertime. The thicker the blubber, the more it insulates the animal. The blubber layer on some types of whales can be up to 19 inches (48 centimeters) thick!

Many animals build up extra layers of fat for the winter. It can be hard to find food during this time. So the animals can use the fat for energy they’re not getting from food. Storing up fat has another important purpose. It keeps animals warm!

Mammals that spend their lives in icy waters need extra fat. This includes whales and seals. “Heat moves through water much faster than air,” says biologist Dominic McCafferty. That means ocean animals can lose heat quicker than those on land.

Whales and seals have a special layer of fat. It’s called blubber. It’s just beneath their skin. This fat keeps them cozy even in frigid water. And it gets thicker in the winter. The thicker the blubber, the more it insulates the animal. Blubber can be up to 19 inches (48 centimeters) thick on some types of whales!

On a snowy day, a bird sits on an ice-covered branch. Suddenly, the bird shakes and then puffs itself up into a big fluffy ball. This may look silly, but the bird is just trying to stay warm! When the air is cold, birds shiver just like humans. Shivering wakes up their muscles and releases heat, says Williams.

But for birds, shivering is just the beginning. Birds have a thick layer of down, or extra-fluffy feathers, next to their skin. Puffing out these down feathers creates air pockets that keep the birds warm. A layer of stiff feathers over the down keeps this trapped warm air from being blown away by the wind.

Still, birds lose a lot of heat through their legs. That’s why you sometimes see birds standing on one foot. They tuck the other leg inside the warm down on their bodies.

A bird sits on an icy branch on a snowy day. Suddenly, the bird shakes. It puffs itself up into a big fluffy ball. This may look silly. But the bird is just trying to stay warm! Birds shiver just like humans when it’s cold. Shivering wakes up their muscles, says Williams. And it releases heat.

But shivering is just the beginning for birds. Birds have a thick layer of down. These extra-fluffy feathers are next to their skin. Puffing out these feathers creates air pockets. They help keep the birds warm. There’s a layer of stiff feathers over the down. It traps the warm air, so it doesn’t blow away in the wind.

Still, birds lose a lot of heat through their legs. That’s why you sometimes see birds standing on one foot. They tuck the other leg inside the warm down on their bodies.

When air temperatures start to drop in Japan’s Jigokudani Snow Monkey Park, troops of snow monkeys know what to do. They climb down from the surrounding mountains to take a hot bath!

In the park’s valleys, pools of water are fed by natural hot springs. These water sources are warmed by heat produced by Earth deep underground. This keeps the pools at a toasty 104°F (40°C) year-round! The monkeys—also called Japanese macaques (muh-KAHKS)—spend winter bathing in these pools.

Hot-water bathing is a rare adaptation, says McCafferty. Most animals try to keep warm by reducing the heat that escapes from their body. Snow monkeys do something different. They absorb heat from their environment. As a result, they don’t need to burn as much fat to keep their bodies warm. That means they can save their energy to look for food, McCafferty explains.

It gets really cold in Japan’s Jigokudani Snow Monkey Park in winter. But troops of snow monkeys know what to do. They climb down from the surrounding mountains. And they take a hot bath!

The park has pools of water. They’re fed by natural hot springs. These water sources are warmed by heat deep inside Earth. This keeps the pools at a toasty 104°F (40°C) all year! The monkeys are also called Japanese macaques (muh-KAHKS). They spend winter bathing in these pools.

Hot-water bathing is a rare adaptation, says McCafferty. Most animals try to keep warm by having less heat escape from their body. Snow monkeys do something different. They absorb heat from their environment. They don’t need to burn as much fat to keep their bodies warm as a result. That means they can save their energy to look for food, says McCafferty.