Birds are not mammals; birds belong to the class Aves and are more closely related to reptiles than to mammals. Mammals belong to the class Mammalia. Birds are the only living animals to have feathers, whereas mammals are the only animals to have hair.
Although both birds and mammals do share a common ancestor, the ancestors of birds split from the ancestors of mammals over three hundred million years ago.
With such a vast amount of time (and evolution) separating birds and mammals, the answer to the question "Is a bird a mammal?" is definitely "no!".
To fully understand why a bird is not a mammal, we need to take a closer look at both groups of animals...
Is A Bird A Mammal?
A bird is a member of the class Aves, a group of animals in the animal kingdom.
You can find out more about birds on this page: Birds: The Ultimate Guide
All of the members of Aves (i.e. all birds, both living and extinct) 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.
Likewise, a mammal is a member of a class of animals called Mammalia. To be a member of Mammalia–and therefore to be a mammal–an animal must have mammalian characteristics.
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...
Brief Guide To Animal Classification: Classes, Orders, Families, Species, Etc.
Both Aves and Mammalia are a "class" of animal. A class is one of several groups into which biologists sort animals (and other organisms, including plants and fungi). The process of sorting organisms into groups is known as classification.
You can find out more about animal classification on this page: Animal Classification.
Within a class, animals are further sorted into groups of animals that are even more closely related to each other. These groups are known as "orders".
The biggest order within Aves is Passeriformes. Over half of all living birds belong in this group. Members of the order Passeriformes are known as passerines. Passerines are also known as "perching birds" or "songbirds".
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 an order.
The largest bird family is Tyrannidae, the tyrant flycatcher family. It contains over 400 bird species.
Bird And Mammal Classification
Biologists classify animals into the above groups by studying the family trees of the animals involved.
Usually, species that are closely related share physical and behavioral characteristics. Animals that are only very distantly related (such as birds and mammals) share relatively few characteristics.
It is the presence (or lack of) certain characteristics that allow biologists to determine to which group an animal belongs.
The characteristics shared by animals in the class Aves (birds) are different to those shared by the animals in the class Mammalia (mammal).
This is because 300 million-odd years of evolution separates birds and mammals; over this time they have become very different animals, and this is why a bird is not a mammal.
Birds Vs Mammals
Despite birds being different to mammals, there are some similarities between the two groups of animals.
This probably explains why so many people ask "are birds mammals?".
Let’s look at the similarities and differences between birds and 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, and maintain a constant body temperature. 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 such as lizards).
- 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.
- Breathe air with lungs: both birds and mammals breathe air, although the lungs of birds and mammals are different. Birds have extremely complex respiratory systems, with air sacs as well as lungs.
Differences Between Birds and Mammals
Although they share certain characteristics, birds and mammals belong to different orders, and there are many differences between the two groups.
A member of the class Aves (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), such as the platypus, lay eggs, but monotreme eggs have softer shells, similar to those of many reptiles.
Birds are avian dinosaurs! All birds are descended from dinosaurs. This explains why birds are related to crocodilians such as alligators and crocodiles; both birds and crocodilians are the descendants of archosaurs which lived in the Mesozoic Era!
A member of the class Mammalia (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 (or fur); if an animal has true hair, then it’s a mammal. (Hair is made of keratin, a naturally occurring protein out of which hooves, horns and fingernails are also made.)
- 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
(In case you weren't sure, insects are animals – you can find out why on this page: Are Insects Animals?)
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 skeletons with hollow bones 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 answered the question "Are birds mammals?", finding that birds are not mammals, being of a different class in the animal kingdom, and separated by over 300 years of evolution.
We’ve found that Aves and Mammalia are both classes within the wider animal kingdom. 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!’
Discover More With Active Wild
- Birds: The Ultimate Guide
- Mammals: An Introduction
- What is a mammal?
- Types of mammal
- Mammal evolution
- Are sharks mammals?
- Is a dolphin a mammal?
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