How Do Mammals Stay Warm?

Polar Bear
Polar Bear

Mammals have adapted to live in a wide variety of habitats, temperatures, and environments. Although mammals all share the same characteristics, I wanted to look into how they survive in these different conditions.

Mammals are endothermic and can regulate the temperature inside their bodies. Mammals regulate their temperature using oxygen, blood circulation, and by turning their food into energy.

If you want to find out how different types of mammals survive, and how they keep warm in extreme conditions, then I have some further information below.

Metabolic Rate

Mammals have adapted to lead different lifestyles in a range of different habitats and environments. The key to this is their metabolic rate. The metabolic rate is a measure of how the chemical processes in the mammal’s cells produce the energy they require for their daily activities.

Their daily activities include internal bodily functions, contraction of the muscles during movement, and the use of the brain in processing information.

The animals also require energy to stop their bodies from cooling down when the conditions are cold.  

Energy is taken from the food that they eat. Carbohydrates and fats are broken down into water and carbon dioxide. Animals have different states of metabolic rate. The lowest is called the basal level.

This is normally when the animal is resting. The highest metabolic rate would be when they are running at their full speed. This is called the maximum level.

Different animals have different measurements of the basal level and maximum level. Mammals have a metabolic rate that is very high compared to other animals.

Whereas a cold-blooded animal like a crocodile would be low, a mammal may have a metabolic rate that is five to ten times as high, even in the resting, basal state.

The high metabolic rate allows the animal to run further, hunt for longer, climb further and swim greater distances, without having to stop and rest.  

The extra heat that is generated from having a high metabolic rate allows the body to be kept at a constant, higher temperature.

This will enable mammals to live in a range of temperatures, ranging from the arctic fox which lives in icy conditions to the pronghorn, which makes its home in hot, desert conditions.

This extra heat generated by their high metabolic rate also allows the mammals to function both during the day and the night.  


This physiology of mammals is called endothermy. This involves their constant, high body temperature, the maximum level of activity, and their high metabolic rate.

The primary source of the heat is due to chemical reactions in the body tissues. This is in contrast to animals that are classed as ectotherms.

Animals such as reptiles and amphibians source their heat from the environment around them, grading them as ectotherms.

Endothermy is linked to almost every part of a mammals life. The high metabolic rate is due to endothermy.

Mitochondria in the cells produce energy, and this energy is distributed through the bloodstream as heat to maintain the temperature of the body. In a mammal that is resting, the major organs such as the brain, intestines, kidneys, and liver produce most of the heat.

Once the animal is moving, the muscles will produce large amounts of heat.

Are all mammals warm-blooded? Find out here in an article I have written.

Photo of white rabbit

How Does a Mammal Keep Their Temperature Constant?

A large amount of heat produced in the tissues keeps the mammal’s body temperature constant above the external heat. By keeping the temperature in the body higher than outside the body, the heat flows away from the body.  

The body of a mammal is very complex, and the temperature inside is continually changing, to let the body know how much of the heat should be transferred away from the skin.

The blood flow to the surface is altered by the changing of the capillaries of the skin. These can be opened or closed as required.  

If the animal is too hot, they will open the capillaries, letting heat out. They will close the capillaries if they are feeling cold.

In mammals with fur, the temperature of the body can be changed by flattening the hair or by fluffing it up. This allows different amounts of air to be trapped in the pelt. If the animal is too hot, they will let more air to get to the body.  

Although the mammal can control its temperature in this way, there are limits to how high or low the animal can regulate their body temperature.  

Thermal Neutral Zone

The thermal neutral zone (TNZ) is a range of temperatures in the mammal’s environment in which they can maintain their average temperature. The thermal neutral zone is based on the mammal not using any energy beyond its lowest metabolic rate.

If the temperature outside the body falls below the TNZ, then the mammal will feel cold. The heat from the body is lost from the skin too quickly, and the animal will cool down.

To combat this, the animal must increase its heat production. This can be done in a variety of ways. To generate extra heat from the muscles, the animal may start to shiver.

This is an excellent way to increase heat over the short term, but over a longer period, such as the winter, they need a different technique. To increase their temperature over a more extended period, they have to increase their lowest base metabolic rate.  

If the external temperature is higher than their body temperature, then the body will not be able to lose heat fast enough through the skin. In this case, their bodies will use evaporation.

The skin will start to sweat from sweat glands. Another way that their bodies deal with this is through panting from the mouth. This releases sweat from the moist membranes of the mouth.

Different species of mammals have different thermal neutral zones which allow them to live in different environments. 

Why Can Mammals Live In Such Different Environments?

Whereas other animals such as amphibians and reptiles rely on the sun for constant body temperature, mammals rely on their bodies to maintain their temperature. By using their bodies, mammals can live in conditions ranging from icy tundra to hot deserts.

Different types of mammals have different thermal neutral zones. The thick fur on an arctic fox allows them to live in conditions of -40 ºC. By raising their activity, the fox can live in temperatures down to -70ºC.

Due to their low TNZ, they do have to be careful not to be active for too long as this can cause them to overheat.

Animals such as the Eastern long-eared bat, have a thermal neutral zone of 36ºC. Below 25℃, the bats enter a state of torpor.

Torpor is described as suspended animation, which they use as they can no longer stop their body temperature from falling any lower.

Hibernation is a longer-term of torpor and is used by some bears, bats, and hedgehogs as a solution to the low seasonal temperatures.

How do Mammals Maintain Body Temperature?

To maintain their high metabolic rate, and in turn, maintaining their body temperatures, mammals require a lot of food. Compared to an amphibian or reptile, a mammal has to eat approximately ten times the amount of food to maintain their body temperature.  


All mammals have evolved to require large amounts of oxygen. The oxygen is essential in maintaining a high metabolic rate.  

When a mammal is at its basal metabolic rate, hardly using any energy, they require less oxygen. The breathing is done by moving the thorax. Muscles and ribs are used to help the thorax contract, drawing air into and out of the lungs.

When the animal is more active, however, the diaphragm is used to aid breathing. The diaphragm, when contracted, increases the volume of the cavity on the thorax, increasing the amount of air that gets into the lungs.  

Blood Circulation

The heart of a mammal is divided into two sides, which is used to ensure that the oxygen that goes to the tissues is richer in oxygen, and also increases the blood pressure in the body, creating a higher flow of blood.

The blood from the left-hand side is sent to the lungs, where it takes up oxygen and gives up carbon dioxide. This blood, freshly-oxygenated, is then returned to the right-hand side of the heart.

The blood is then pumped again, but this time to the tissues of the body delivering oxygen and carbon dioxide.  


Mammals spend most of their lives eating and have evolved different ways of doing this. Mammals have a special kind of teeth, which are prepared for eating the type of food in their environment.

The teeth make biting, tearing, and chewing makes digestion more straightforward and faster.

Different types of mammals have evolved stomachs that are unique from others. Ungulates such as cows have a stomach that is divided into four sections. These make it easier to digest the massive amounts of plant material that they require to keep their high metabolic rate.  

If you want more information on how a cow’s stomach works, I have written an article. You can find this hereOpens in a new tab..

Some mammals do not use teeth to eat. Anteaters use a sticky tongue to swallow ants whole. Some marine mammals use a row of teeth to eat fish.

Mammals can breathe and eat at the same time using a bone that separates the airway from the nostrils and lungs to the mouth below.

How do Young Mammals Keep Warm?

Endothermy works in mammals, but for young mammals, it can be problematic. The larger a mammal is, the slower they lose heat. This is due to the higher surface area compared to volume. Consequently, the small the mammal, the faster they lose heat from their bodies.  

Where some ectotherms can be very small, endotherms such as mammals cannot survive if they are too small.

Pregnant mothers have to create an environment to protect the young from the temperatures outside their body. They need to control the temperature around them, providing all the nutrients that the embryo needs.

In most mammals, the embryo is kept in the uterus until the young are ready to be born, allowing the baby to develop without regulating their own temperature.

Once born, some small mammals, such as mice are born very small. The environments they are kept in once born need to be provided by the mother. These can be in the form of a nest or burrow.

For other mammals such as humans, whales, and large herbivores, the embryos are kept inside the mother’s body for a much longer time, giving them enough time to maintain their body temperature once born.  

Want to know how deer keep warm in winter. They have some amazing adaptation which you can read here.



A constant body temperature for a mammal allows them to be active at all times. This gives them more considerable time to hunt, feed, and attract mates over a longer period.

Most mammals do not need to hibernate through the winter, given them extra time in their lives. Time can also be spent hunting and feeding throughout the night, not just the day.

A few species do hibernate, but these are generally small mammals that live in higher latitudes of the continent. Due to the increased periods of activity, mammals can live on land, in rivers, lakes, swamps, seas, and oceans.

Integrated Activities

Most physical and chemical processes that a body goes through are temperature sensitive. Chemical reactions, contraction of the muscles, blood flow through vessels, and the rate of diffusion of molecules all rely on the body being vulnerable to temperature.

Mammals are integrated systems that consist of these and many more processes being linked to one another.

Changes in temperatures can break down these processes, causing the integrated systems to stop working. Mammals are more complex than ectotherms and have more integrated processes happening at one time.  

With the increased complexity comes a narrower change in body temperature that can be tolerated. A reptile would have the brain size one-tenth of that of a similar-sized mammal.

When a mammal dies due to being too hot or too cold, the actual cause of death is due to a failure of a part of the function of the brain, whether this is heart failure or loss of respiration.

Maximum Aerobic Metabolic Rate (MAMR) (AKA – Why the hare would beat the tortoise in a race)

Endothermy allows mammals a higher level of sustainable activity. Mitochondria in the cells of the internal organs contribute to the basal metabolic rate and constant body temperature.  

Mitochondria are also present in large number in the muscles of a mammal. Their role is to provide energy for the muscles. They break down the glucose by oxidation.

This process allows them to provide the mechanical energy for the contraction of the muscles. By having a large number of mitochondria in the muscles, the amounts of glucose can be increased, increasing the amount of energy.

The maximum aerobic metabolic rate (MAMR) is approximately ten times of a reptile of the same weight. A mammal and a reptile of the same weight can run roughly the same speed.

However, the mammal can run for far longer. The reptile cannot provide extra glucose to the muscles and will run out of energy. The mammal can run further, using the energy from its food, until they run out of glucose to be oxidized.

Although the mammal is continuously using up its energy stores, they can constantly hunt, forage, fight, evade predators, find new food sources and search for mates.

Ever wondered how the arctic fox survives in extreme temperatures. This article I have written hereOpens in a new tab. should answer all your questions.

Bryan Harding

Bryan has spent his whole life around animals. While loving all animals, Bryan is especially fond of mammals and has studied and worked with them around the world. Not only does Bryan share his knowledge and experience with our readers, but he also serves as owner, editor, and publisher of North American Mammals.

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