What Are The Differences Between Mammals And Birds?

It is relatively easy to tell the difference between a bird and a mammal at a glance, but there are some differences between them that you may not know.

Birds differ from mammals in that they have feathers, a lighter bone structure, the method in which they feed, and their respiratory, circulatory, and digestive systems.

To find out more about the differences between mammals and birds, please read on.

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What Are The Differences Between Mammals And Birds?

There are many differences between mammals and birds, including their outer skin coat, bone structure, feeding method, and auditory structure. We will go into the details of all these differences below.

Outer Coat

The first difference that many people notice between mammals and birds is that birds generally have feathers. Birds have feathers because they need to keep their bodies light and well ventilated. Mammals have fur or hair as their outer coat, which they use to keep themselves warm. Mammals are endothermic animals and regulate their temperature.

If you want to know the differences between mammals and amphibians, I have written an article which you can find here.

Bone Structure

Birds have to be very light to be able to fly, and one of the reasons they are so light is their bone structure.

The primary reason for this is that birds have hollow bones. The hollow bones enable them to keep their weight on the lower side, which helps them fly. On the other hand, mammals have denser bones.

Over several centuries of evolution, the bird bones have become hollow to fly to greater heights. If the bones were denser like mammals, they would not fly due to their heavier weight.

While this difference is not visible by looking at them, it is one of the primary differences between mammals and birds.

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Feeding method

Mammals have mammary glands, and that is how they got their name. Mammals use mammary glands to feed milk to their young.

When you look at birds’ feeding method, you will realize that they provide partially digested food or easy to digest food to their young. 

Unlike mammals, they do not feed milk from their body to their young. Birds do not have mammary glands to produce milk. This is why birds provide easy to digest food to their younger ones, which they get external to their bodies.

There are many differences between mammals and insects.  Find out what they are here

Auditory structure

Another big difference between mammals and birds is how they produce sound. The auditory system between birds and mammals is entirely different.

Mammals use a part known as the larynx. The larynx in mammals is situated near the upper area of the neck. It is responsible for breathing and producing sound in mammals. The larynx consists of the vocal folds to vary the pitch and volume.

Birds do not have a larynx but instead have a syrinx. The syrinx is the auditory organ which birds use as a voice box. The syrinx does not consist of any vocal folds. The mechanism used to produce sound involves the variation of membrane tension to modulate the sound. The absence of vocal folds ensures that the sound produced by birds and mammals is starkly different.

You may know that insects have six legs and spiders have eight, but do you know all the other differences?  Find out more here.

As you can see, how mammals and birds produce sound is entirely different. The variation is not just based on the modulation technique but also the different body parts in use.

Respiratory System

If you are familiar with our own respiratory system, you may know that we use the lungs to inhale and exhale. The exchange of oxygen and carbon dioxide takes place inside microscopic sacs in the lungs. Lungs are an essential part of the respiratory system of humans and other mammals.

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Birds have a different respiratory system. Bird exchange oxygen and carbon dioxide in the air capillaries. The air capillaries are similar to microscopic tubes.

The respiratory system differs in mammals and birds because the exchange process happens in a single cycle in mammals. In birds, however, the exchange process occurs in 2 different cycles. This means that oxygen is kept in the body for two complete inhalations and exhalations.  

This paramount difference in the respiratory system makes mammals and birds quite different from each other.

Birds are diverse in their size, colors, diet, and other ways.  Find out more in this article I wrote

Mouth Anatomy

The next difference between birds and mammals is much easier to notice when looking at them. Mammals have strong teeth, which help them with the mechanical digestion of food.

Birds do not have teeth but instead have a beak. The beak does not contain any teeth. The mechanical digestion of food takes place through gastroliths. Gastroliths are small stones they swallow into the stomach to help them grind down food particles.

Not only the anatomy of the mouth is different but also the digestion process of mammals and birds.

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Reproduction System

One of the most basic differences between mammals and birds is the difference in their reproduction system.

Mammals directly give birth to their younger ones. Birds, on the other hand, lay eggs. They then warm these eggs and take care of them in their nest until the eggs hatch, and the young ones are born.

Sound Processing Capability

Birds have a huge advantage when it comes to auditory capacity. They have the highest resonant frequency per cm square of their body surface. Mammals cannot produce sounds at such a high resonant frequency. 

This means that mammals are generally not able to produce sound at higher resonant frequencies than birds.

There are at least 22 species of owl in North America.  Find out what they are in this article I wrote

What Are The Similarities Between Mammals and Birds?

Now that you are aware of the primary differences between mammals and birds, I wanted to let you know some similarities.


Birds, as well as mammals, maintain constant body temperature. Both birds and mammals are warm-blooded. Birds or mammals do not make use of external heat to stay warm.

This warm-blooded nature gives rise to another similarity. It means that when mammals and birds’ calorific requirement is taken into account concerning weight, it is quite similar.

Wild horses

The warm-blooded nature of mammals and birds ensures that they have to consume a significant amount of food to maintain body temperature. The dietary requirements of both these species are much higher than cold-blooded animals such as reptiles.

Heart Anatomy

Mammals have a four-chambered heart, but you might be surprised to find that birds also have the same.

Birds are only able to fly by spending a significant amount of energy. Generating such a large amount of energy is only possible with an efficient circulatory system. That is why birds require a four-chambered heart to circulate enough blood to generate the required amount of energy.

The four-chambered heart of mammals and birds separates the oxygenated and deoxygenated blood and pumps the oxygenated blood to various parts of the body.

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Raising Young

While the feeding of the young is different in mammals and birds, other methods are the same.

Both mammals and birds look after their younger ones. However, the time for which the mammals and birds look after their younger ones vary from one species to another.

In the case of mammals, the female mammal generally looks after the younger one while lactating, while in the case of birds, most species look after their younger ones until they can fly and hunt prey.

There are a few variations in each of these species, but this is a general rule.

Nightjars are fascinating birds.  Find out how they hunt in this article I wrote.


Vertebrates are living organisms consisting of a backbone and a skeletal system. They can move around swiftly and easily without requiring external support at all points in time.

Birds, as well as mammals, are vertebrates. While birds do have hollow bones, their bone structure is much more complex. The anatomy of a bird\ ensures that the bones can easily take their bones’ support while landing and taking off. Mammals, on the other hand, have dense bones that allow them to walk and run easily.


Blood Composition

Another similarity between mammals and birds is the composition of their blood. Blood consists of white and red blood cells. In both cases, the red blood cells contain hemoglobin, which is a protein used by the body to transport oxygen. In both mammals as well as birds, the blood is red due to the presence of hemoglobin.

If you want to know the differences between mammals and insects, I have written an article which you can find here.

Sources and References





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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