Are Birds Mammals, Reptiles,
Or Something Else? And Why?

Are you curious to know whether birds are categorized as mammals, reptiles or something else? Read on to find out more.

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David A. Swanson

October 04, 2021

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What’s This Post About?

Birds are the kind of animals most people are fond of because of their unique plumage and ability to fly to different locations. Various other animals are only bound to their respective habitat; however, birds choose to live differently by moving to different areas.

It might not be hard to believe that about 400 billion birds are living on the planet as of now; however, some people still find it hard to figure out if birds are mammals or reptiles or something entirely different.

However, birds have an easily identifiable characteristic feature— their feathers— that make them stand out among other animals.

Birds are neither mammals nor reptiles; they are warm-blooded vertebrates characterized by their distinctive feature— feathers. However, just like birds and mammals, reptiles also fall under the category of vertebrates according to biological classification.


Are Bird Mammals, Reptiles, or Something Else?

Birds neither belong to the group of mammals nor are they reptiles; however, birds belong to a classification of vertebrates known as ‘Aves’ in the animal kingdom. All of the animals in the Aves group share the same characteristic.


Mammals, reptiles, and aves are all classes of animals listed in the animal kingdom. Even though there are some significant similarities between mammals and birds, like both classes consist of vertebrates, endothermic, and have four-chambered hearts, they are grouped separately because of the differences in their characteristic features like feathers and beaks.


Birds or ave class is further divided into species which is the lowest level of classification, and there are about 9702 species of birds that have been classified to date. However, due to variation in each species at different locations, there are also many subspecies.

How are Birds Different from Mammals?

All birds do have feathers; however, some bizarre birds like kiwi have hair-like feathers. Besides, kiwis also have heavy bones and are unable to fly too. Moreover, they also have nostrils at the base of their beak, making them different from other birds.


One of the most prominent and noticeable features that make birds apart and unique from other classes like mammals and reptiles is their feathers.

The bodies of the birds are entirely covered by feathers which either help them take flight or provide insulation to maintain the warmth of their body, whereas mammalian skin only has hair.

Another difference is that birds lay eggs with hard shells; however, most mammals give birth, and even if they lay eggs, their eggs have soft shells.

Unlike mammals, birds do not have forelimbs, but they have wings. Another difference is that birds do not have teeth; however, they have beaks only to swallow food whole or break it into tiny bits with their sharp beaks.


Birds can be found doing weird stuff, but they are way more intelligent than we assume. For example, Cardinals and many other bird species occasionally wrap themselves in crushed or living ants. This allows the ants to crawl on them. It is believed that these birds do this to let the formic acid that gets secreted during the bath help them get rid of lice or any parasite.

How are Birds Different from Reptiles?

Only birds are the kind of living animals that have feathers. It is compulsory for all animals under the class of birds to have feathers, and even some birds have specialized feathers for particular functions like a peacock's tails, etc.


The reason that birds and reptiles are different classes is because of the characteristic differences they have. One of the significant differences is that reptiles have scales on their bodies; on the other hand, birds are fluffy because their skin is covered with soft plumes and feathers.

The one similarity that birds share with reptiles is their scaly legs.

Present-day reptiles are all carnivores except a few. On the other hand, birds have an entirely different diet compared to them.

Most reptiles do not even have legs; however, birds have legs with their forelimbs as wings. Moreover, there is a high variation in the body’s shapes in reptiles, and in birds, there is always a streamlined shape.


Birds can be found in a variety of sizes. Some birds are tiny, like the bee hummingbird, the smallest bird, ranging from 5 to 6.1 centimeters. However, there are other large birds like the ostrich that have large-sized eggs and have big eyes as well.

What are the Similarities between Mammals and Birds?

Birds are capable of replacing their old and scarred feathers with new ones through molting. Birds only perform molting either after nesting or before they're planning to migrate with the sufficiency of resources and energy.


Despite major differences between birds and mammals, there are also some similarities among both of them. One of the similarities is that both of these classes come under vertebrates classification, which means both mammals and birds have backbones.

Moreover, both birds and mammals are warm-blooded animals which means they can regulate their body temperatures.

Warm-blooded animals can warm themselves when the surrounding is cold by mechanisms like shivering; hence, unlike reptiles, they do not need to move to any warmer location.

Both birds and mammals have four-chambered hearts, which is a way more efficient system than the three-chambered hearts that most reptiles have.

What Are the Similarities Between Reptiles and Birds?

Even though all birds must have feathers, some baby birds are born without feathers. Most of the birds hatch completely naked and grow downy feathers over time.

Most of us already know that birds and reptiles both lay eggs outside their bodies, unlike mammals which is one of the most significant similarities between them.

Moreover, both birds and reptiles have a similar skeletal structure in which five fused bones make the jaw. This is precisely why birds and some reptiles have similar-looking faces.


Another similarity is that they both belong to the same ancestors. Both birds and reptiles have evolved from theropod dinosaurs that were reptiles having three-toed feet and hollow bones. Dinosaurus also incubated their eggs, just like how birds and reptiles do now.



Most birds have very lightweight and strong bones that facilitate their flying; however, a few flightless birds have solid bones that are also heavyweight because of bone marrow.

Do Birds Mate Like Mammals or Reptiles?

There are various species of birds where the male and female birds look different from each other. One of the most common examples is the peacock, where the female does not have the long tail to dance.

You might not be surprised to know that birds mate in a completely different manner than mammals. Birds do not have penises; however, both male and female birds have cloaca instead.

The cloaca of a bird is an internal chamber, and this chamber ends in an opening through which the birds’ sex organs discharge sperm or eggs.

Since birds have different mating seasons, whenever the seasons arrive, their cloacal openings swell, extending slightly outside the bodies.

The male birds’ sperm stored in his cloaca is deposited into the female’s cloaca upon rubbing their swollen cloacas. Later it drifts up the chamber, eventually fertilizing the eggs.



A bird's heart beats way faster than a human's heart. If we compare, hummingbirds' heart beats up to 1260 times per minute while a human heart can only beat 60-100 times a minute.

Is Every Flying Animal a Bird?

For ages, people have long believed that every animal that flies is a bird. It was also believed that bats are birds, which they are not.

Like birds, bats also fly through the air, and you can notice them taking flights around the time when it’s almost hard to distinguish them from birds. However, bats are way different from birds because they belong to class mammalian.

In addition, bats, unlike birds, give birth to babies instead of laying eggs. Not only this, but they also produce milk to feed their newborns. Where birds only have beaks, bats have teeth with jawbones to chew their meal.

One of the most apparent differences is that bats don’t have feathers, but they have skin membranes on their wings.



Even though we have always associated flying with birds, not all species of birds pass this criteria. Some birds do not fly throughout their life span, and examples of those birds include ostrich, penguin, emu, cassowary, kiwi, and rhea. However, all the birds must have two wings even if they can't fly.

Do Birds Eat Similar Food as Mammals and Replies?

The food habits of birds can be variable according to their species. There are different kinds of birds munching on different types of food at different phases of their lives.

A particular bird species might only eat seeds throughout its life; however, its hatchlings feed on insects and other protein-rich foods to attain the optimum energy required.

Some birds only feed on fruits throughout their lives, while others like to enjoy their favorite flowers’ nectar. Nevertheless, this is not much different from reptiles and mammals, as there are different food habits found in both reptiles and mammals. All of these classes have omnivores, carnivores, and herbivores as well.


Why Do Birds Have Higher Metabolic Rates Than Mammals?


The reason behind birds having high metabolic rates is their high body temperature. Birds have higher body temperatures as compared to mammals. For example, their body temperatures range from about 38 - 42 degrees C in small birds; however, large flightless birds like ostrich, emu, and some aquatic birds like penguins have slightly lower temperature ranges.

Aquatic birds and other large birds have similar body sizes as mammals; hence their body temperature is also identical. This means such birds also have slower metabolic rates than the different bird species with smaller body sizes.


Keep Reading!

Birds are vertebrate animals and are one of the five subdivisions of vertebrate animals, including fishes, amphibians, reptiles, and mammals. This indicates that birds are neither mammals nor reptiles. Instead, they are an entirely separate class.

Birds have ancestral similarities with reptiles, but they are way different from them. For example, where reptiles have scales on their body, birds have feathers.

Similarly, birds also do not belong to the mammalian class as they have different characteristic features. For example, mammals have skin membranes instead of feathers, and they reproduce by giving birth, unlike birds.

If reading up on birds interests you, I would recommend you head over to this post to read about whether birds are cold-blooded or not and whether they freeze to death or not.

Are Birds Cold-Blooded? Why Don't They Freeze To Death!?

Are you wondering whether birds are cold-blooded and why don’t they freeze to death? Read to learn more.

David A. Swanson Picture

By David A. Swanson

Bird Watching USA

My name is David and I'm the the founder of Bird Watching USA! I started Bird Watching with My father-in-law many years ago, and I've become an addict to watching these beautiful creatures. I've learnt so much over about bird watching over the years that I want to share with the world everything I know about them!

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David A. Swanson Picture

David A. Swanson

Bird Watching USA

My name is David and I'm the the founder of Bird Watching USA! I started Bird Watching with My father-in-law many years ago, and I've become an addict to watching these beautiful creatures. I've learnt so much over about bird watching over the years that I want to share with the world everything I know about them!



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