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Bats are considered mammals, but as the only flying mammal, people often ask me why they are mammals, not birds. In this article, I look to determine whether they possess all the mammalian traits.

Bats are mammals because they breathe air, give birth to live young, provide milk to their young, have fur, and are warm-blooded.

Many people think that bats are classed as birds. I wanted to clarify this misconception, so in this article, I look at why bats are classed as mammals, not birds.

When thinking about flying animals, we think about birds of all shapes and sizes, including the bald eagle and the cardinal. However, bats are flying animals but are not classed as birds but as mammals.

Bats evolved over 52 million years ago with an intriguing and complex history. How they gained the ability to fly is a mystery, as there is a lack of fossilized evidence. Because of this, the ancestor of modern bats is unknown.

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Are All Bats Mammals?

Chiroptera refers to an order of mammals that incorporates over 1,400 species, including more than 40 species in North America.

All species of bats carry the significant mammalian traits of being warm-blooded, having fur, mammary glands, and breathing air.

Chiroptera belongs to the eutherians group as they do not lay eggs or possess pouches and give birth to live young after an extended gestational period. Bats then continue parental care with lactation, providing milk until they are young and independent.

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What is a Mammal?

A mammal is a warm-blooded animal with fur that feeds its young milk. They also have lungs and, therefore, breathe air. The obvious examples of a mammal are humans, dogs, and cats. 

However, marine animals such as dolphins, whales, dugongs, and manatees are also classed as mammals as they possess all of these traits.

The order of Mammalia includes animals that possess mammary glands. The ranking incorporates monotremes (egg-laying mammals), such as echidnas, duck-billed platypi, and Marsupials (mammals with pouches), such as kangaroos and possums. The third includes Eutherians, which are known also known as placental mammals. Eutherians have a long gestation period, as evidenced by humans carrying their young for nine months.

Next, we look at how bats show these typical mammalian traits.

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Do Bats Have Fur?

One of the more subtle features of bats is that they have fur. Some people believe that bats have feathers, but this is not correct.

Many people do not know whether bats have fur as they do not have hair on the largest parts, the wings.  

However, bats have fur on their bodies and sometimes on their heads. The different colors can include brown, gray, tan, and red.

Most bats are not born with fur, but some are. Fruit bats are born with hair, but most are born hairless, with their pink bodies showing.

Hair is not necessary for bats like many other mammals, such as dogs or cats. Most animals use their fur to keep warm, but bats can drop their body temperature to between 7 degrees and 10 degrees centigrade.

Are Bats Warm-blooded?

Cold-blooded animals, such as snakes and lizards, are ectothermic, meaning they use the outside temperature to regulate their body temperature. 

Bats, as part of the mammalian group, are warm-blooded and are classed as endothermic homeotherms. Bats must maintain their body temperature using the energy they convert from food.  

Bats will conserve energy by dropping their body temperatures down. When they do this, they also fall their heart rate to as low as ten beats per minute.

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Bat Reproduction

As most land mammals do, bats give live birth to their young after a gestation period. The gestation period can last between six and nine weeks in most bats.

During this time, as placental mammals, the baby is connected to the mother by an umbilical cord, just like humans. They share blood, which provides the young with nutrients and removes waste products using the mother’s internal organs.

Bats give birth while hanging upside down. The young are born, caught, and placed inside the mother’s pouch. Most bats give birth to one young, although some species can give birth to up to four.

Bats are small, about one inch when born, but can weigh up to a quarter of their mother. They are born with gray fur.

The young are fed milk until they are about three weeks old. At this age, they are already almost full-size. The young will try to learn to fly at this age.  

At about six weeks old, the young will have learned to fly and will be able to catch insects instead of relying on their mother’s milk for sustenance.

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Do Bats Breathe Air?

As with all mammals, bats breathe air to take in oxygen. Bats have lungs, which they use as part of their respiratory system to exchange air, take in oxygen, and expel carbon dioxide.

Baleen bats have two nostrils, whereas toothed bats only have one. Bats cannot breathe through their mouths as the trachea is not attached to it, so the blowholes on their heads are their only means of oxygen intake. This separation removes the risk of the airway opening when food is swallowed underwater.

Bats have developed an exceptionally efficient respiratory system and have a larger lung volume than other non-flying mammals. Bats can utilize 60% of their lung capacity with each breath.

Bats produce a protein called myoglobin, which allows them to sustain flight. Myoglobin is useful for facilitating oxygen transfer from the blood to the muscle.

The Bat Wing

Even after millions of years of flight, bats still have the same bone structures as land mammals. When studying a bat’s wing’s bone structure, it is possible to see that the wing is similar to a human arm.  

The wing has a much more flexible structure and a skin membrane between the hand and the body. The thumb can be seen as a claw. This claw helps them to climb.

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Echolocation is another difference in bats that not many other mammals share. Echolocation in mammals is restricted to bats, whales and dolphins. Bats are the only land mammals that use echolocation.

Although bats can see in the dark, echolocation gives them an edge to fly at night.  

Bats can ‘see’ at night using echolocation. They project sound waves out, and the echoes arrive back with information on what is in the surrounding area.

Echolocation is extremely good with bats as they can determine thin objects. Using echolocation, bats can find food in the dark and navigate.


With the characteristics of breathing air, having fur, and feeding their young milk, bats are the same as other mammals.

However, over millions of years, the ancestors of today’s bats were able to adapt to their environment, which provided them with an untapped supply of insects and the ability for flight and echolocation.

Even though they live in an environment different from most other mammals, they can utilize the unique properties that allow them to stay members of the mammalian group.

There are four different groups of marine mammals.  Find out what they are in this article I wrote.