Is A Bird A Mammal?

Is a bird a mammal? If you’ve been reading the articles in our mammals section, then you’ll know the answer to this question!

Are Birds Mammals?

The answer to ‘Is a bird a mammal?’ is NO; a bird is NOT a mammal. On this page, we’re going to find out why!

A bird is a member of Aves, a group of animals in the animal kingdom. All of the members of this group have certain things in common. These shared characteristics are what make birds birds. If an animal doesn’t have all of these characteristics, then it belongs in a different group.

Superb Fairywren
Birds are members of the class Aves. This is a Superb Fairywren from Australia.

Likewise, a mammal is a member of a group of animals called Mammalia. To be a member of Mammalia – and therefore to be a mammal – an animal must again have certain characteristics.

Mammal Sumatran Tiger
Mammals are members of the class Mammalia. This is a Sumatran Tiger, a member of the cat family, Felidae.

Although there are some similarities between birds and mammals, there are also many differences between the members of each group. Read on to discover what those differences are …

Animal Classification

Both Aves and Mammalia are ‘classes’ of animal. A ‘class’ is one of several groups that scientists sort living things into. This process is known as ‘animal classification’.

You can find out more about animal classification here: Animal Classification. Here you’ll see how a wolf is classified from kingdom level down to species level.

Within a class, animals are further sorted into groups of animals that are even more closely related to each other. You may have heard of people talking about an animal ‘family’. An animal family – such as Canidae, the dog family – is a subgroup of animals within a class.

Animals are sorted depending either on their physical characteristics or on their family tree (which usually – but not always – amounts to the same thing).

The characteristics shared by animals within the Aves (bird) class are different to those shared by the animals in the Mammalia (mammal) class. This, in a nutshell, is why a bird is not a mammal.

However, there is some overlap between the characteristics of birds and mammals. This is where the confusion arises.

Let’s look at the differences (and the similarities) between birds and mammals.

Adelie Penguin Facts For Kids
Even flightless birds such as this Adélie Penguin are definitely NOT mammals!

Birds Vs Mammals

Similarities Between Birds and Mammals

Although birds and mammals are very different types of animal, they do have certain characteristics in common:

  • Vertebrates: both birds and mammals are vertebrates, which means that they have backbones.
  • Endothermic (warm-blooded): both birds and mammals are endothermic (warm-blooded). This means that they are able to regulate their own body temperatures. For example, warm-blooded animals are able to warm themselves up when cold (e.g. by shivering); they don’t need to move to a warmer location or bask in the sun like cold-blooded animals).
  • Four-chambered hearts: the hearts of both birds and mammals have four-chambers. This is a more efficient system than the three-chambered hearts of amphibians and most reptiles.

The Differences Between A Bird and A Mammal

Although they share certain characteristics, birds and mammals are very different animals. Let’s find out why.

Bird Characteristics

A member of the Aves class (i.e. a bird) has the following basic characteristics that are not shared by mammals:

  • Feathers: birds’ bodies are covered by a number of different types of feathers. Feathers help with flight, and also with insulation (keeping the bird warm).
  • Beaks and no teeth: birds don’t have teeth, and have to swallow their food whole, or cut it up into manageable bits with their beaks. A bird’s beak is often highly-specialised according to its diet.
  • Egg-laying: all birds lay eggs with hard shells. Some mammals (called monotremes) lay eggs, but monotreme eggs have softer shells, similar to those of many reptiles.

Mammal Characteristics

A member of the Mammalia class (i.e. a mammal) has the following basic characteristics that aren’t shared by birds:

  • Hair: mammals are the only group of animal to have hair; if an animal has hair, then it’s a mammal!
  • Give birth to live young. All mammals – apart from the five monotreme species – give birth rather than laying eggs.
  • Feed their young with milk. All female mammals feed their young with milk. This highly nutritious liquid is produced by structures called ‘mammary glands’, from which mammals get their name. No other type of animal can produce milk.

You can find out more about what makes a mammal a mammal here: What is a Mammal?

Bird Adaptations For Flight

Bat Flying Mammal
It’s not just birds that can fly: a bat is a flying Mammal

Being able to fly is not a defining characteristic of birds: bats are mammals, and they can fly. Some reptiles and amphibians too can glide (although strictly, this isn’t flying).

However, all birds – even flightless birds such as penguins and ostriches – are descended from animals that could fly, and their bodies reflect the adaptations required for flight.

The most obvious adaptation for flight is a bird’s wings. They are the bird’s forelimbs. By flapping their wings, most birds can take off, glide, and power themselves through the air.

Most birds have lightweight, hollow skeletons to aid flight. Birds have high metabolisms (the amount of energy required to live), and have to eat large amounts of food. This is mainly because flying requires a great deal of energy.

In addition to lungs, birds have a number of air sacs inside their bodies. This helps to move air in and out of a bird faster. This too is a necessity due to the high metabolism of birds.

Is A Bird A Mammal: Conclusion

On this page we’ve looked at the differences between birds and mammals. We’ve found that Aves and Mammalia are both classes. We’ve found that a member of Aves is a bird, and that a member of Mammalia is a mammal. We’ve also looked at the differences (and similarities) between birds and mammals.

So, the next time that someone asks you ‘Is a bird a mammal?’, you’ll be able to say ‘No, a bird is NOT a mammal!’.

Other mammal pages:

Enjoyed This Article?

If you enjoyed this article, feel free either to share it on social media using the buttons at the top of the page, or link to it from your own website.

12 thoughts on “Is A Bird A Mammal?”

  1. Crocodiles/alligators are reptiles and armadillos aren’t the most direct example there is. But yes, I suppose.

    • Hi,

      That’s a great question!

      Alligators are not descendants of dinosaurs. Although alligators and dinosaurs are both reptiles, their ancestors split into two separate evolutionary branches millions of years ago.

      You can find out more on this page: Are Dinosaurs Reptiles?

      Armadillos, despite looking a bit reptilian with their scaly armour, are mammals, not reptiles. Armadillos are definitely not descended from dinosaurs!

      We hope this helps. If you have any more questions, feel free to ask!


      The Active Wild Team

  2. I think that dinosaurs aren’t really in a class because (a) they don’t exist anymore, and (b) birds and reptiles are descendents of dinosaurs.

    • Just because a species is extinct does not mean it’s classification no longer exists. Would we say this of species that have gone extinct in more modern times? No we wouldn’t.

      Your second comment has validity.

      Birds and reptiles can be classed as dinosaurs, but dinosaurs cannot be classed as birds or reptiles. Evolution only works in one direction.

    • Hi, thank you for your comment.

      Dinosaurs are reptiles. They, along with all other reptiles, belong to the class Reptilia.

      There were reptiles living on Earth for many millions of years before dinosaurs appeared, so reptiles are not descended from dinosaurs.

      Birds are descended from dinosaurs, but are usually put in their own class: Aves.

      We hope this helps! If you, or anyone else, has any questions, feel free to ask!

      The Active Wild Team

  3. So a bird is a dinosaur. but is a dinosaur a mammal? or is it a bird? Or is it a reptile?! What is a dinosaur then? I would think it’s a bird, but I am pretty sure they feed their baby milk also. we don’t have enough proof to me that a dino is a bird a mammal or whatever. please reply if I am just dumb. Jurassic park got meh confused

    • Evolution only goes one way, so a bird could be classified as a dinosaur, but a dinosaur would not be classified as a bird. Hope this clears things up.

      Kind regards.

    • Hi!

      Great questions!

      Birds are descended from dinosaurs. Dinosaurs are reptiles (not mammals), and today, many scientists regard birds as being reptiles!

      HOWEVER, birds are usually put in a group of their own (Aves), rather than being thought of as reptiles.

      Only mammals feed their young with milk.

      You can find out more about this subjects on these pages on ActiveWild:

      Mammal Facts
      Reptile Facts
      Bird Facts
      Dinosaur Facts

      We hope this helps!

      The Active Wild Team

  4. But don’t pigeons produce milk? What about how feathers and fur descend from a common substance and therefore are classified as the same? A chicken was born without a beak and instead with a dinosaur like face, with your classifications, that bird is either a dinosaur or a mammal. I am curious about the validity of your points. Can someone please explain? Thank you.

    • Hi,

      Thank you for your email. You bring up some great points.

      Pigeon ‘milk’ is not really milk, although it serves the same purpose (feeding the young). It is a thick substance that forms in the pigeon’s crop – a food storage area behind the bird’s throat.

      Mammalian milk is formed in a female mammal’s mammary glands. Mammary glands are modified sweat glands. No other type of animal produces milk.

      Yes, mammals share similarities with birds – they have the same (distant) ancestors – buts it’s the differences that separate the two groups!

      Birds are the only remaining descendants of dinosaurs. In fact, many scientists today regard birds as being dinosaurs!

      You can find out more about this here: Dinosaur Evolution

      I hope this helps!


Leave a Comment