I find this question a lot on the internet and I thought I really needed to make an article that perfectly explains what birds are mammals and why.
If you already searched on the internet for an answer to this question, then you surely know that most websites will argue that no birds can be considered mammals, and then they go ahead and explain why in long and boring articles.
Although you can’t say that there are no mammal birds, this list is in fact very short: There is only one bird that can be considered a mammal as well.
The Kiwi bird is the only bird that is also referred to as a mammal, although it is considered an honorary one. What makes this bird also a mammal is its physical characteristics, general behavior, and habits, all of which are pretty unusual for birds but very similar to other mammals.
You can’t argue the fact that kiwis are a one-of-a-kind type of creature. Throughout history, the ancestors of kiwi birds managed to develop a lot of mammalian characteristics, mainly due to a shortage of land mammals at the time. This is what made this small bird adopt an eco niche very similar to hedgehogs and other land mammals and completely different from other birds.
Together with cassowaries, rheas, ostriches, and emus, kiwis belong to the group of flightless birds. A kiwi will basically be the size of an adult domestic chicken.
The kiwi was named an honorary mammal because of some very specific features and characteristics that can’t be found in other birds.
Fun fact: The kiwi’s eggs are the largest of all birds on Earth in proportion to their body size.
The kiwi chicks are almost instantly ready to take care of themselves and feed themselves, as soon as they hatch. This makes them seem like small adults rather than chicks. This is a very unusual characteristic for birds.
You will also notice that the plumage of a kiwi will look very similar to animal fur and not like normal feathers, which is very unusual for birds. Their beak will also have some very unusual, mammalian-like whiskers on their beak.
Kiwis also have really bad eyesight, another unusual thing for a bird species. They are, in fact, not far from being completely blind. This won’t cause them a lot of problems, as they are nocturnal creatures and they will rely on their other senses.
It is very common for birds’ eye sockets to be separated by a plate, but this isn’t the case for kiwis, who have nasal cavities just like most of the mammals.
The most important senses these mammal birds would use to catch prey and protect themselves will be their smell, touch, and auditory senses. The kiwi’s beak will have nostrils at its end. This makes it the only bird with nostrils, but nostrils are a common trait in mammals.
These birds will use the nostrils from the end of their beaks to catch insects and worms that live underground, without the need to see them.
The kiwi will also have bones that are more similar to mammals. With the majority of birds having hollow bones, kiwis will have bones with marrow instead.
The average body temperature of the kiwi will also make it more similar to mammals than birds. The body temperature of this bird is 39 to 42 Celsius, just two to four degrees higher than mammals.
They will also dig burrows, another trait more common in mammals like badgers than in birds.
Birds are essentially creatures with warm blood, belonging to the Aves class. They are vertebrate bipedal creatures that are usually covered with feathers.
Scientists estimate that all around the planet, there are anywhere between 50 and 430 million birds.
Birds are known to have descended from a feathered theropod. This means that you could even consider them living dinosaurs still roaming around.
Birds usually have a very light skeleton, made of hollow bones that have no marrow.
Birds lay eggs as a way of reproduction. They have a beak that is toothless.
Although not all birds are able to fly, they have wings from their past ancestors.
One thing you might not know is that their respiratory system is one of the most complex on earth. This is because they have a very unique way of getting oxygen through breathing.
Most birds (kiwi is not one of them, of course) have very good eyesight, in addition to ultraviolet eye cones.
Adult birds will feed their young with digested food. Most birds are very social and will live in big groups. They also communicate using visual signals, calls, songs, and other sounds.
The group of animals from the Mammalia family are called mammals. There are currently around 130 billion mammals all around the world, the scientists believe.
Although most of the mammals are quadrupedal, meaning they use four legs for locomotion, some will use just two, while others have adapted throughout time to live underground, in trees, or in water.
As opposed to other animals, from other animal families, mammals have hooves, paws, and hands. They also have bones that are dense and have marrow in them.
Another physical characteristic that distinguishes mammals from other groups of animals is hair or fur.
A few mammalian animals are considered intelligent, being able to use a few different ways to communicate and some of them even use tools. Their communication also includes echolocation, alarm signals, scent-making, or singing, among others.
Their level of desired socialization doesn’t make them any different from any other animals. This means that some of them like to live in groups of all sizes, others like to stay solitary, and just a few of them will even have hierarchized socialization.
Mammal species are the only ones to have mammary glands. They are used to produce milk, which would be consumed by their babies.
All mammals have in common a reproduction system where they give birth to live babies.
Mammals are known to be a vital part of the human feeding sector. It helped people throughout history move away from farming and hunting and getting into farm animal raising.
Mammals and birds are not only part of completely different groups of animals, but they are also very easy to distinguish.
The kiwi bird is the only one that seems to be part of both, because of its very unusual traits. It has a lot of characteristics of a mammal but it still clearly belongs to the group of birds. This is why scientists are really conflicted as to what group is best for these animals