When it comes to the animal kingdom, there are a lot of different classifications that exist. The question of "Are birds mammals?" has been a topic of debate for a long time. In this comprehensive guide, we'll take an in-depth look at the question of whether birds are mammals. Why can't birds consider mammals? The key differences and similarities between these two types of animals.

Are Birds Mammals?

First, let's start with the answer: Birds are not, in fact, mammals. While both birds and mammals are animals that can be found all over the world, birds belong to the class Aves, while mammals belong to the class Mammalia. They have very different physical and biological characteristics.

Let's follow up the following content of mammal definition and the reason to know why!

What is a Mammal?

A mammal is a type of vertebrate animal known for its unique characteristics. It belongs to the warm-blooded vertebrates constituting the class Mammalia. According to its reproduction methods, they are further classified into three broad groups :

  • Egg-laying: Monotremes like the platypus and echidna
  • Marsupials: Carry their young in a pouch such as kangaroos and koalas
  • Placentals: the young develop within the mother's body before birth. It includes most familiar mammals like cats, dogs, and humans

Characteristics of Mammals

Mammals have several key characteristics to help people identify whether an animal is a mammal. Let's know more about the characteristics that distinguish mammals from other animals one by one!

Hair or Fur

Mammals have hair or fur covering their bodies. This feature not only does fur provide insulation, keeping animals warm in cold environments, but it can also help with camouflage, mating, and even communication. Like sheep have fur all around their body.

Mammary Glands

Mammals have mammary glands that produce milk to nourish feed their young. This is a key feature that separates mammals from other types of animals and is a defining characteristic of the class. Like the most commonly seen creature when we mentioned milk: cow. Or our human is the easiest understand example!

bird feed their young

Live Births

When it comes to reproduction, mammals mainly give birth to live young rather than laying eggs. This allows for a greater degree of parental care and nurturing, which can result in stronger and more well-adapted offspring.


All mammals are endothermic, or warm-blooded. Warm-blooded animals maintain a constant body temperature through consuming food metabolic processes in the body or physical activities. They have the ability to maintain a stable internal body temperature regardless of external environmental conditions.

Advanced Brains & Highly-developed Senses

Another key feature of mammals is their highly-evolved nervous system. Mammals have complex brains that allow for advanced cognitive functions. Such as problem-solving, communication, and social behavior.

Additionally, many mammals have highly-developed senses such as sight, hearing, smell, and touch, which they use to navigate their environment and hunt for prey. This combination of advanced sensory organs and cognitive abilities is what makes mammals such a unique and fascinating group of animals.


Mammals have a diaphragm, a muscle that separates the chest and abdominal cavities and aids in breathing. It enables efficient breathing and plays a role in several other physiological functions! For example, it assists in vomiting, urination, and defecation by increasing intra-abdominal pressure.

Three Middle Ear Bones

Mammals have three middle ear bones, which transmit sound from the eardrum to the inner ear. These bones are unique to mammals and allow for sensitive hearing.

Bird Ear Bones

Why Birds Aren't Usually Considered Mammals

Maybe the mammal definition and its features are clear, and you still can't understand well Why birds can't be described as mammals. Like birds have features, some mammals also birth via laying eggs...

Actually, the reasons for this distinction lie in the unique physical characteristics, reproductive strategies, and evolutionary history of birds that set them apart from mammals.

1. Birds have feathers but not fur or hair

Yes, birds have feathers, but this is different with the mammal's fur or hair all around their body and maintaining a suitable body temperature. Feathers are unique to birds and provide insulation, protection, and the ability to fly. They are made of keratin, the same protein that makes up hair and nails in mammals, but the fact is that not a single mammal has feathers.

2. Birds lay eggs similar to some monotremes like the platypus and echidna

Birds all lay eggs to reproduce. Bird eggs have hard, calcified shells for protection. And bird typically incubates their eggs by sitting on them to warm the eggs and reproduce. Although some monotremes are born by laying eggs, they are different.

3. Birds do not have mammary glands to feed their young

After hatching, bird chicks are often cared for by one or both parents. But birds don't have mammary glands to feed baby birds. Instead, they produce a nutritious substance called crop milk in their crop, a specialized part of the digestive system. They will find food outside like bugs, and seeds to feed young birds.

What's more, based on other features of birds, here are also the points

1. Brain Size and Structure

Birds have smaller brains than mammals, but they are still highly specialized and complex. They have a different brain structure than mammals, with more emphasis on visual processing and less on the sense of smell.

2. Birds can fly

Birds can fly Many birds are capable of flight, which sets them apart from all other animals except insects. Flight requires a specialized body structure and a high metabolism to generate the energy needed to stay aloft.

Bird fly

3. Respiratory System

Birds have a distinctive respiratory system that is more efficient at extracting oxygen from the air than that of mammals. They possess nine connected air sacs that function like bellows, maintaining a one-way airflow through the lungs.

On inhalation, air enters the nostrils, travels down the trachea, and moves into the lungs via two bronchi. Here, gas exchange occurs in tiny tubes called Parabronchi. Unlike mammals, who have a tidal airflow in and out of the lungs, birds' air flows in one direction, enhancing gas exchange efficiency.

4. Birds have beaks instead of teeth

Birds have beaks instead of teeth. The shape and size of the beak are adapted to the bird's diet and lifestyle. And also different bird's beak has different uses, woodpeckers, use their beaks to excavate or drill holes in trees to create nests or find insects to eat. And, eagles and hawks, use their strong, hooked beaks to tear apart prey.

bird beaks

Similarities Between Birds and Mammals

Despite these differences, birds and mammals do share some common traits.

Endothermic (warm-blooded)

Both birds and mammals are endothermic, meaning they can regulate their body temperature internally, regardless of the external environment.


Birds and mammals belong to the group of animals known as vertebrates. They all have a backbone or spinal column.

Four-chambered hearts

Birds and mammals both have a four-chambered heart, which allows for the efficient separation of oxygen-rich and oxygen-poor blood.

Red and white blood cells

Both birds and mammals also have red and white blood cells, which are responsible for carrying oxygen and fighting infections.

Advanced brains

Another similarity is that both birds and mammals have advanced brains. This allows them to learn, solve problems, and remember information. This cognitive ability has allowed them to become the most successful groups of animals on Earth.

Parental care:

Most importantly, both birds and mammals exhibit a significant amount of parental care for their young. It is uncommon in many other groups of animals. Mammals nurse their young with milk produced by mammary glands, while birds feed their young with regurgitated food. Any bird will build their nests for laying eggs and provide shelter and protection for their offspring.

After birth, the bird parents will search kind of food for their young birds day by day. It is similar to our humans to feed our children and company their growth. Until the young birds can fly themselves, this process will end.

It is really a very lovely and interesting process that you can observe and learn. This includes nest building, egg laying, incubation, and the emergence of chicks from their eggs.

birdfy nest with 2 cameras

bird nest record

By observing these processes, you can learn about the lifecycle of birds, their reproductive strategies, and how they care for their young. It's a fascinating aspect of bird behavior that offers a glimpse into the diversity and complexity of nature.

If you are interested in observing and learning about birds firsthand, you can try to observe this process by using Birdfy Nest - a smart birdhouse with dual HD close-up cameras and AI recognition to help you observe birds' nesting and hatching.

Birdfy Nest

The Birdfy Nest is designed to provide a natural environment for birds to build their nests. It's made from eco-friendly materials! Safe for birds! And it contributes to a sustainable environment.

birdfy nest features

The product encourages birds to engage in their natural nesting behaviors, offering observers a unique opportunity to learn about bird nesting and hatching processes. It's also easy to install in your backyard, garden, or balcony and can attract a variety of bird species. The Birdfy Nest is more than just a home for birds! It's a gateway to understanding and appreciating the wonders of avian life.


In conclusion, birds are not mammals, and they have unique characteristics that set them apart. While they share some similarities with mammals, such as advanced brains and parental care, they are a separate class of animals.

Birdfy works harder for bird feeder cameras to help you observe and know more birds when feeding. Let's follow Birdfy to know more about these beautiful feathers!

More Resources

To learn more interesting fun facts about birds, please read our following blogs:

1. How do birds mate?

2. Some fun facts about Great tit

3. Black-chinned hummingbird

4. Spiritual meaning of birds flying into your house?


August 01, 2023 — Noah William

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