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Are Chickens Mammals or Birds?

Nicole Cosgrove

Chickens are not mammals as they have wings and feathers which make them a species of bird and further classified as fowls. Many people do not know that chickens are not mammals at all. There is much debate over the correct term that should be used to describe the chicken’s biological nature and there is much confusion on this topic.

If you want to find out more about using the correct term for chickens and what type of class they belong to, then this article has all the answers for you.

new chicken dividerChicken Classification

In comparison to mammals, chickens are not classified as Mammalia, but rather Aves which shows that scientifically, chickens are not related to mammals. Chickens also do not share much genetic relation to mammals and the classification differences between the two are vastly different.

Species: G. gallus
Genus: Gallus
Class: Aves
Order: Galliformes
Kingdom: Animalia
Family: Phasianidae

Surprisingly, chickens are not closely related to mammals, but rather to reptiles. The evolving process between chickens and mammals is not the same, and there are more characteristics in chickens that intertwine with reptiles than mammals, however, chickens are neither of these. Instead, they are members of the bird order Galliformes.

close up of chickens in the farm
Image Credit: Capri23auto, Pixabay

What Makes Chickens a Bird?

The chicken has feathers, wings, a beak, warm-blood, and lay eggs. These are all common characteristics associated with birds. They share the same classifications, and all share a common ancestry. Furthermore, a bird’s digestive system is slightly different than mammals, as they use their proventriculus for food storage and a gizzard which is the muscular part of the stomach that uses grit to grind grains into finer particles.

As with most birds, the chicken’s reproductive system is broken up into two parts: the oviducts and ovary. The yolk develops in the ovary and is then released into the oviduct. Unlike mammals, birds’ ovaries release the next ovum several minutes after an egg has been laid.

  • Prolific egg-laying
  • The ability to fly (although chickens can only flap their wings and glide)
  • A typical skeletal structure of a bird
  • Have a crop, gizzard, a proventriculus, and a cloaca
  • Have only one stomach
  • Monogastric

Why Are Chickens Not Mammals?

The confusion on this subject stem from the controversy over the features and behaviors that chickens display which can overlap with certain mammal and reptilian creatures which has led many people to believe that chickens are mammals or reptiles, or something closely related to the two.

Let’s take a closer look as to why chickens cannot be classified as a mammal:
  • Mammals are covered in hair or fur, whereas chickens have feathers instead. This is because mammals and birds evolved from very different groups of animals. Mammals evolved from synapsids a couple of million years ago, whereas birds evolved from dinosaurs 150 million years ago. Feather also gives birds the ability to fly or glide, whereas fur has a much different role. However, chickens are flightless birds due to their heavy body structure from selective breeding.
  • Mammals are warm-blooded and great at controlling their body temperature. Chickens need to stay warm to be healthy and their regular bodily operating temperature is between 105° to 107° Fahrenheit. This is slightly warmer than mammals. This can also indicate why feathers have insulating plumage to help keep them warm.
  • Chickens lack mammary glands which is one of the most prominent characteristics of a mammal. These glands produce milk for the nursing mammals to sustain their young. Chickens do not have these glands and do not nurse their young. Even though some species of birds produce crop milk, it is still not linked to mammary glands.
  • Mammals give birth to live young (except for the platypus and echidna), whereas chickens lay eggs that then hatch into their offspring. The reproductive system works differently than mammals.
  • Chickens also lack the teeth that mammals use to chew their food. Instead, chickens have a beak.
  • Chicks do not rely on their mother to feed them, whereas young mammals will feed off their mother’s milk. Baby chicks will only rely on their mother for warmth, but chickens do not produce crop milk to nurse their chicks.

Featured Image Credit: Ivdonata, Shutterstock

Nicole Cosgrove

Nicole is the proud mom of Baby, a Burmese cat and Rosa, a New Zealand Huntaway. A Canadian expat, Nicole now lives on a lush forest property with her Kiwi husband in New Zealand. She has a strong love for all animals of all shapes and sizes (and particularly loves a good interspecies friendship) and wants to share her animal knowledge and other experts' knowledge with pet lovers across the globe.