Are Birds Mammals?

Written by AZ Animals Staff
Published: September 7, 2021


Birds are not mammals, but avians. Unlike mammals, they do not have fur or hair — instead, they have feathers, though sometimes they possess bristles on their heads or faces that resemble hair. They are not mammals even though they are warm-blooded, breathe air, and possess vertebrae, which are other mammalian characteristics. They’re not mammals even though some species gather in flocks for foraging, hunting, childrearing, and protection the way mammals do in herds.

Birds exclusively lay eggs. Some, like chickens, can even lay eggs without a male, but those eggs are infertile. No bird gives live birth. Many are intensely protective of their young, but (and this is the big thing) no bird nurses its young with milk the way mammals do.

Branches serve as perches for birds to stand, climb and play.

But Don’t Pigeons Feed Their Babies With Milk?

Pigeons and doves don’t feed their babies with milk, even though it may look like they do. Pigeon “milk” is a substance that’s made from fat and protein-rich cells that line the parents’ crop, which is a pouch found in the throat that stores food before it’s sent to the rest of the gastrointestinal tract to be digested. Like the milk produced by mammals, it not only has proteins and fats but antioxidants, antibodies, and helpful bacteria. It is even controlled by prolactin, the hormone that controls mammalian lactation.

But crop milk is semi-solid, not liquid, and it isn’t delivered through teats, secreted from patches like it is for the echidna, or in grooves like it is for the platypus. It is regurgitated from the parent to the squab. The squab is fed crop milk exclusively for the first week after it hatches. Flamingos and emperor penguins also feed their chicks with something like crop milk. By the way, both the mother and the father produce crop milk, another thing that makes them different from mammals. Only female mammals produce milk for their young.

How Do Birds Take Care of Their Young?

Chicks are born naked, blind, and helpless and need at least one parent to protect them, feed them and keep them warm 24 hours a day for a surprisingly long time. The great frigatebird, for example, takes care of its chicks for nearly two years.

Squabs are first fed crop milk while other chicks are fed soft-bodied insects or bits of other prey such as small mammals, reptiles, and birds that are smaller than their parents or part of the parents’ regurgitated dinner. Even after some chicks fledge, or start to grow feathers, they will demand that the parent feed them for several weeks. Some chicks are so labor-intensive to raise that not only do both parents do it, but they enlist the help of their previous brood of chicks.

On the other hand, the chicks of scrubfowls and brush turkeys are independent almost from birth, and they don’t need any parental care at all. Others such as the cuckoo simply lay their eggs in another bird’s nest and hope it doesn’t notice. Interestingly, the foster parents often do not notice, and there are many pictures of some tiny bird delivering food to a chick that’s already twice its size and has managed to kill off all the biological offspring.

A parent bird has to burp its food into the mouth of its young.

More Reasons Why Birds Aren’t Mammals

Another thing birds have, that most mammals don’t, are wings. Not every bird can fly. In some cases (as with the emu) their wings are vestigial. The only mammals that have proper wings are bats. Bats can actually outmaneuver birds because their wings are actually their hands.

Birds are the only living therapod dinosaurs, and many scientists actually consider them a type of reptile. They are younger than reptiles or mammals, having appeared about 140 million years ago. The asteroid that killed off the other dinosaurs 60 million years ago allowed birds to diversify into a dazzling array of forms, from the tiniest hummingbird to the 9-foot tall ostrich.

Another thing that separates avians from mammals is their skeletons. Birds have hollow places in their bones that allow them to fly, which is why even the tallest ostrich only weighs about 286 pounds even though it gave up flying a while ago.

Next Up: Are Owls Mammals?

FAQs (Frequently Asked Questions) 

Are birds endangered?

Like other orders of animals, whether a bird is endangered depends on its species. Some, such as European starlings, are not only of least concern but in some places they’ve become invasive. Others are critically endangered. They include the kakapo, the world’s only flightless parrot, that’s now confined to a few islands in New Zealand. The ivory-billed woodpecker of North America is so endangered that it may be extinct. About 1200 species of bird are considered endangered due to habitat loss, overhunting, pollution and other human activities.

How many species of birds are there?

Scientists believe there are between 9800 to 10,758 avian species. That’s much more than the 6400 extant species of mammals.

What kinds of birds are there?

Biologists divide avians into two main groups. They are the passerines and the non-passerines. Passerines are often described as songbirds even though birds such as ravens and crows belong to this group. Some claim it may be more accurate to describe passerines as birds that perch and non-passerines as birds that don’t perch, even though parrots and birds of prey, which perch perfectly well, are considered non-passerines.

Why do birds have feathers?

Feathers and fur are made out of the same material, keratin. But feathers are better than fur because they not only keep birds warm and dry but allow birds to fly. They also allow them to attract mates in ways that fur doesn’t. Many male birds in particular take on a brilliantly colorful or extravagant breeding plumage during their mating season. Feathers also allow flocking birds to blend in with other members of their flock. This makes it hard for any predator to pick out one individual.

Another interesting thing about feathers is that most blue feathers aren’t blue because of pigment but because of the way the light strikes them.

Are birds omnivores, herbivores or carnivores?

They are all of the above! The pigeons who have adapted to urban life will eat anything, even human trash. The same is true of seagulls that visit landfills. Birds of prey and seabirds such as skuas are carnivores. Penguins eat fish and other marine life small enough for them to handle. Hummingbirds sip nectar. Sparrows, parakeets, grosbeaks and finches eat seeds. Toucans, blackbirds, hornbills and tanagers and vireos eat fruit, though some of these same animals eat both fruit and seeds. One interesting thing is that even herbivorous birds often feed their babies worms and insects simply because they need the protein and fat that these foods provide.

Are birds dangerous?

Most birds aren’t that dangerous to humans, though large birds of prey such as harpy eagles have huge talons that can inflict injury. The kick of an ostrich is potentially fatal as is the kick of a cassowary. This flightless bird, which is found in Australia and New Guinea, has the equivalent of a knife blade on its outer toe and has been known to eviscerate creatures it considers to be threatening, including humans.

Do all birds migrate?

Not all birds migrate, but those that do may fly thousands of miles to places where they only breed and back to the places where they feed and perform other activities of life. If they live in a place that is always abundant in food and whose climate they find tolerable year round, they tend not to migrate. The Arctic tern has one of the longest migrations of any creature. It breeds in the Arctic and winters on the coast of Antarctica. Some birds, such as parakeets, are nomadic. They’ll fly long distances to find food, but they’ll remain in the same habitat and region.

How long do birds live?

Birds can live a surprisingly long time, and unlike humans they don’t appear to age. The kakapo, the endangered New Zealand parrot, can live to be 100 years old, allegedly. Ravens and albatrosses have lived into their 60s, and even hummingbirds, with their speeded up metabolism, can live to be as much as 14 years old. One rule of thumb is that long-lived avians are larger, have fewer chicks, take longer to reach maturity, live in the trees and live on islands.

What do humans use birds for?

Humans use birds for all kinds of reasons, which is a blessing and a curse. They are used for their meat and eggs and for their feathers. Indeed, ostriches and egrets were nearly driven to extinction just because milliners wanted to use their feathers to adorn their hats. Bird guano is used for fertilizer. Many birds are kept as pets, others such as falcons and cormorants are used to help humans hunt and fish. Other birds are hunted. Sometimes, like the passenger pigeon, they are hunted to extinction. Many people simply watch birds and set up feeders in their yards to attract them.