Hibernation vs. Brumation: How Animals Survive Extreme Seasons

When food disappears and the weather turns harsh, some animals simply power down. Here is how hibernation and brumation work, and how they differ.

When winter settles over the mountains of northern Pakistan, the landscape changes completely. Snow buries the pastures, streams freeze, and insects vanish. For many animals, the season is not just uncomfortable. It is a food crisis. There is almost nothing to eat, and staying warm burns energy that cannot be replaced.

So what do you do when you cannot leave, cannot find food, and cannot afford to stay awake? Some animals have discovered a remarkable answer: they shut down. Marmots curl up in underground burrows. Bears retreat to dens. Lizards and snakes slip into cracks and tunnels and stop moving for weeks or months.

You have probably heard of hibernation. You may also have come across a less familiar word, brumation, especially if you keep reptiles as pets. They sound similar, and in some ways they are, but they are not exactly the same thing. This guide explains both in simple, beginner-friendly language, along with a few related survival tricks, examples from Pakistan, and ways to help animals through the toughest season of the year.

The Problem: Surviving When Life Gets Hard

Living things need energy, and energy comes from food. In places with extreme seasons, such as freezing winters or scorching dry summers, food can become scarce for months at a time. Animals have three basic ways to deal with this:

Move away. Many birds, whales, and other animals migrate to places where conditions are better.
Stay active and adapt. Some animals grow thicker fur, change their diet, or store food to eat later. Squirrels bury nuts, and wolves and snow leopards keep hunting through the snow.
Slow down. Other animals reduce their energy needs so dramatically that they can get by on stored body fat, or on very little food, until conditions improve.

The third strategy is called dormancy, and hibernation and brumation are two forms of it. Think of it like putting a phone in battery-saver mode: the animal still exists, but it is doing the bare minimum to stay alive.

A Quick Word About Torpor

Before we get to hibernation, we need one more term: torpor. Torpor is a temporary state in which an animal lowers its body temperature, heart rate, and breathing to save energy. It can last for a few hours or a few days.

Hummingbirds are a good example. They burn energy at an astonishing rate, and on cold nights some of them enter torpor to avoid running out of fuel before morning. Some small bats do the same during the day.

Hibernation, in simple terms, is long-term torpor that lasts for weeks or months through winter. Torpor is the basic tool, and hibernation is the seasonal, extended version.

What Is Hibernation?

Hibernation is a long period of deep inactivity during which a warm-blooded animal sharply reduces its body temperature, heart rate, breathing, and energy use. It is mainly seen in mammals, along with a few birds.

Warm-blooded animals, called endotherms, normally keep their bodies at a steady temperature by burning fuel. That is expensive in winter. Hibernation allows the animal to turn down its internal thermostat and save huge amounts of energy.

What happens inside a hibernating animal?

The changes can be dramatic:

Body temperature drops. In some small hibernators, such as ground squirrels, it can fall to just a few degrees above freezing. The Arctic ground squirrel has been recorded with a body temperature slightly below the normal freezing point of water without turning to ice.
Heart rate slows. A heart that normally beats hundreds of times a minute may drop to only a few beats per minute.
Breathing becomes slow and irregular. Some animals may pause for long periods between breaths.
Energy use falls dramatically. A hibernating animal may use only a small fraction of its normal energy, which allows it to live off stored fat.

Getting ready: the feast before the fast

Hibernation does not just happen suddenly. In late summer and autumn, animals go through a period of heavy eating called hyperphagia. They pack on fat, which will be their only fuel during the long sleep. A marmot or bear that fails to gain enough weight before winter may not survive.

The surprising wake-ups

Hibernators do not stay in one deep state the entire time. Many wake up briefly every so often, warming their bodies back up for hours or days before cooling down again. Scientists are still studying exactly why. Theories include the need to restore certain body functions, clear waste, or sleep in the ordinary sense. These warm-ups are costly. A large share of the energy used during hibernation is spent on these brief wake-ups, which is why disturbing a hibernating animal can be dangerous for it.

Who hibernates?

Marmots and ground squirrels, which spend the winter in deep burrows
Hedgehogs, in species from cold climates
Dormice, which are famous for sleeping for months
Many bats, which hibernate in caves and old buildings
Some small primates and marsupials in other parts of the world
The common poorwill, a small North American bird, one of the few birds known to hibernate

What about bears?

Bears are probably the first animals people think of when they hear “hibernation,” but they are a special case. Bears spend the winter in dens and do not eat, drink, or pass waste for months, but their body temperature only falls a few degrees, and they can wake up fairly easily. Many scientists prefer to call this a form of winter sleep or a lighter type of hibernation.

There is an even more remarkable detail: female bears give birth in the den during winter. The tiny cubs feed on their mother’s milk while she lives off her fat reserves. Researchers are also fascinated by the fact that bears seem to avoid the loss of muscle and bone that would normally follow months of inactivity.

What Is Brumation?

Brumation is the term commonly used for the winter dormancy of reptiles and sometimes amphibians. If hibernation is a mammal’s way of powering down, brumation is the reptile version.

The key difference lies in how these animals handle body heat. Reptiles are ectotherms, often called cold-blooded. They do not generate their own body heat the way mammals do. Instead, they rely on the outside environment, basking on warm rocks to heat up and retreating to shade to cool down. When winter arrives and temperatures drop, their bodies naturally slow down. They become sluggish, eat very little or nothing, and seek a sheltered spot to wait out the cold.

How brumation works

Activity drops. Reptiles stop hunting and spend most of their time hidden away.
Metabolism slows because the body is cold, rather than because the animal “decides” to turn down a thermostat.
Appetite shrinks. Many reptiles stop eating completely for weeks.
Short wake-ups are common. On a warm day, a reptile may emerge to bask or drink water, and then return to its shelter.
Shelters matter. Snakes often gather in underground dens, rock crevices, or burrows, sometimes in large numbers. Lizards tuck into cracks or burrow into the ground. Turtles may rest in the mud at the bottom of ponds.

Some astonishing amphibian tricks

Amphibians such as frogs and toads also go dormant in cold conditions. Some do it in remarkable ways.

Wood frogs in North America can survive being partly frozen. Their bodies produce natural antifreeze-like sugars that protect their cells while ice forms between them. They thaw out in spring and carry on as if nothing happened.
Pond turtles that spend the winter underwater at the bottom of a frozen pond can survive with very little oxygen. Some can even absorb a small amount of oxygen through their skin and other tissues.

A note on the word “brumation”

It is worth being honest here: “brumation” is a popular term, especially among reptile keepers, but not every scientist uses it. Some researchers simply use “dormancy” or even “hibernation” for both groups. The word is useful because it reminds us that reptile dormancy works differently from mammal hibernation, but the boundary between the two is not perfectly sharp.

Hibernation vs. Brumation: The Key Differences

Here is a simple side-by-side comparison in words.

Who does it? Hibernation is mainly done by mammals (and a few birds). Brumation is done by reptiles and, in some cases, amphibians.
How is the body controlled? In hibernation, a warm-blooded animal actively lowers its own thermostat and body temperature. In brumation, a cold-blooded animal slows down mainly because the surrounding temperature drops.
How deep is the “sleep”? Hibernators are often in a deep, unresponsive state with very low heart rate and breathing. Brumating animals are typically less active and sluggish, but they may be more easily roused and can sometimes move, drink, or bask on warmer days.
Do they wake up? Both can wake up periodically. Hibernators spend a lot of energy warming themselves, while brumating reptiles tend to wake when the environment warms.
What do they live on? Hibernators rely mostly on stored fat. Brumating reptiles also use stored energy, but their needs are far lower because their bodies are cool.

The simplest way to remember: hibernation is an active energy-saving strategy by warm-blooded animals, while brumation is a slow-down that comes from being cold-blooded in cold weather.

Not Just Winter: Summer Sleepers and Pausing Insects

Extreme seasons are not only cold. In hot, dry places, some animals go dormant to survive the summer. This is called aestivation.

Lungfish in Africa and elsewhere can bury themselves in mud and seal themselves in a cocoon of dried mucus, surviving for months until the rains return.
Desert snails seal their shells to avoid drying out.
Some frogs and toads burrow underground during dry months and emerge when the rains arrive.

Insects have their own version. Diapause is a pause in development that lets insects pass through harsh seasons as eggs, larvae, pupae, or adults, only resuming growth when conditions improve.

Dormancy in Pakistan

Pakistan’s diverse climate means that many of these strategies can be found here.

In the high mountains, the Himalayan marmot spends much of the year in its burrow system. In places like the Deosai Plains, marmots fatten up through the short summer and disappear underground when winter arrives. The Himalayan brown bear, too, retreats to a den during the harshest months. These sleeping animals are a hidden part of the mountain’s food web, and their emergence in spring is a sign that the season has turned.

In the plains and deserts, many reptiles reduce their activity during the cooler months. The spiny-tailed lizard, found in the dry regions of Sindh, Punjab, and Balochistan, is known to spend the cold season in its burrow. Snakes become less visible in winter, and then reappear when it warms up, which is why people often encounter them more in spring and summer. Frogs and toads also respond to the rhythm of the weather and appear in huge numbers once the monsoon rains arrive.

Hot and dry stretches may also trigger forms of summer dormancy in some insects and amphibians, though this is less well studied.

If you live in Pakistan, you may not see hibernating animals directly, but you are living alongside them. Their quiet sleep is part of what keeps local ecosystems running.

When the Seasons Change Too Fast: Threats to Dormant Animals

Dormancy is a delicate strategy, and it depends on predictable seasons. Today, those patterns are being disrupted.

Climate change. Warmer winters and earlier springs can wake animals too early or change the timing of food availability. If a marmot emerges before plants have grown, or before the snow has melted, it may find nothing to eat. Studies of marmots in North America show that earlier emergence can occur as springs warm, and scientists continue to explore the consequences.
Disturbance. Noise, construction, tourism, and human activity near dens, caves, and burrows can wake animals when they cannot afford the energy. Every unplanned wake-up burns precious fat.
Disease. In North America, a fungal disease called white-nose syndrome has caused huge losses in hibernating bat populations by causing them to wake up repeatedly and burn through their fat before spring.
Habitat loss. Without safe places to den, burrow, or shelter, animals cannot go dormant safely. Cleared forests, drained wetlands, and paved ground reduce these hiding places.
Pollution and chemicals. Pesticides and other chemicals can build up in animals’ fat stores and become dangerous when the fat is burned.

Why Scientists Study Sleeping Animals

Hibernation is not only fascinating. It may hold clues for human medicine and technology. Researchers are studying how hibernators:

Survive extremely low heart rates and body temperatures without damage
Avoid muscle and bone loss despite months of inactivity
Protect their brains and organs when blood flow is low

These discoveries may eventually help scientists find better ways to treat conditions such as stroke or heart problems, or even to protect astronauts on long space trips. These ideas are still at the research stage, but they show how much we can learn from animals.

A Special Note for Reptile Keepers

If you keep a pet reptile such as a bearded dragon, tortoise, or snake, brumation may be a natural part of its yearly cycle. In winter, it may become less active, eat less, and sleep more. This can worry owners, because the same signs can also appear when a reptile is unwell.

A few general points:

Do not assume. Reduced appetite and activity may be brumation, but they can also be signs of illness, poor temperature, or improper lighting.
See a vet who knows reptiles if you are unsure, especially if your pet is losing a lot of weight, has trouble breathing, or looks unwell.
Provide the basics. Fresh water, a safe and quiet shelter, and a suitable environment are important.
Do not force feeding or activity without professional advice.

Because every species is different, the best approach is to learn about your specific animal and consult an experienced reptile vet.

How You Can Help Dormant Animals

You do not need to be a scientist to protect animals during their sleep.

Leave natural shelter in place. Piles of leaves, logs, rocks, and long grass give hedgehogs, reptiles, and amphibians places to hide.
Be careful in the garden. Check before digging, moving wood piles, or burning leaf heaps in winter. You may disturb a sleeper.
Avoid pesticides and chemicals that can harm animals and the insects they eat.
Respect wildlife areas. Stay away from dens, burrows, and caves, and keep noise low in nature reserves.
Support habitat protection. Wetlands, forests, grasslands, and mountains are crucial homes.
Do not handle wild animals you find dormant. If you find one in an unusual place or in danger, contact a local wildlife rescue or expert instead of moving it yourself.
Take climate action. Saving energy and reducing waste helps keep seasons more predictable for wildlife.

Common Myths About Hibernation and Brumation

Myth: Hibernating animals are just asleep. Fact: Hibernation is much deeper than normal sleep, with huge changes in body temperature and heart rate. In fact, hibernators still need to sleep in the ordinary sense now and then.

Myth: All animals hibernate in winter. Fact: Many animals stay active, migrate, or use other strategies. Hibernation is only one of several solutions.

Myth: Reptiles hibernate exactly the way mammals do. Fact: Reptile dormancy, often called brumation, depends heavily on environmental temperature and works differently.

Myth: Waking a hibernating animal is harmless. Fact: Each arousal burns a large amount of stored energy, and repeated disturbances can be deadly.

Myth: Bears are the only big hibernators. Fact: Bears are famous, but they are not the deepest hibernators. Many smaller animals, like ground squirrels and dormice, go much deeper.

A Few Quick Questions

How long can animals stay dormant? It depends on the species and climate. Some small mammals may hibernate for six months or more, while reptiles may brumate for weeks or months depending on temperature.

Do hibernating animals eat? Mostly no. They live off stored fat. Some may nibble on stored food during wake-up periods.

Can birds hibernate? Very few do. Most birds migrate or stay active. Some use short-term torpor to save energy, and the poorwill is a rare example of a bird that can enter long periods of deep torpor.

Do fish hibernate? Some fish become much less active in cold water and rest on the bottom, which is a form of dormancy, though it is usually described differently from mammal hibernation.

Final Thoughts: Nature’s Pause Button

Hibernation and brumation show how creative life can be in the face of hardship. Where one animal flies thousands of kilometres and another grows a thicker coat, others simply press pause. They reduce their needs, hide in safe places, and trust that spring will return.

For us, these sleeping animals are a reminder of how closely nature is tied to the rhythm of the seasons, and how delicate that rhythm can be. When we protect habitats, give wildlife space, and take care of the climate, we help ensure that the pause button works