Yes, a chicken is considered a bird. Chickens belong to the biological class Aves, which contains all bird species. As members of the pheasant family Phasianidae, chickens share many common characteristics with other birds such as feathers, wings, a beak, and laying hard-shelled eggs. While there are some unique aspects to chickens, they clearly fit the criteria for being classified as avian creatures.
What makes something a bird?
In biology, birds are characterized by a number of anatomical and physiological traits. All birds have feathers, wings, lay eggs, and have a four-chambered heart. Other common features include having a beak with no teeth, a lightweight but sturdy skeleton, excellent eyesight, high metabolic rate, unique respiratory system, and more.
To be considered a bird, an animal must possess the following:
Feathers
Feathers are a hallmark of all bird species and perform a variety of functions. They provide insulation to retain body heat, allow for flight, repel water, attract mates, and provide camouflage. Feathers grow uniquely in birds, developing from epidermal cells in the skin.
Wings
The forelimbs of birds are modified to form two wings, which provide lift and thrust to enable flight. Wings have long feathers attached to the skeletal structure to create an airfoil surface. The wingspan and shape are adapted for different flight styles from soaring to diving.
Laying hard-shelled eggs
All birds lay eggs with calcified outer shells made mostly of calcium carbonate. This provides protection, gas diffusion, and safe incubation for the developing embryo. The egg size, shape, color, and number vary between species.
Beak with no teeth
Birds have a keratinized beak or bill used for eating, grooming, killing prey, and more. While other animals may have beak-like mouths, no birds have true teeth. They swallow food whole, grind it in their gizzard, or tear it with sharp edges on the beak.
Lightweight but sturdy skeleton
A bird’s skeleton is well-adapted for flight. Pneumatic bones, hollow vertebrae, fused tail vertebrae, keeled sternum, and other modifications create a rigid and lightweight framework. The fusion helps withstand the stress of flapping/flight.
High metabolic rate
Birds have very high metabolisms to generate enough energy for flying and maintaining a high, stable body temperature. Their normal body temperature ranges from about 38 to 42°C. Smaller birds have a faster heartbeat.
Efficient respiratory system
Birds have a complex respiratory system with air sacs that ventilate the lungs and extend into the hollow bones. This facilitates gas exchange and allows for sustained aerobic activity required for extended flights.
Excellent eyesight
Birds have large eyes relative to their head size and excellent vision at long distances. Raptors (e.g. hawks, eagles) have some of the sharpest vision among animals. Most birds see in color, have UV sensitivity, and can detect rapid movements.
Other features
In addition to the above, birds may display these other characteristics:
– Egg tooth for breaking out of the shell
– Crop for food storage before digestion
– Cloaca excretory opening
– Bony tail turned into a ploughshare, pygostyle
– Scales on legs, feet
– Oviparous reproduction
– Nucleated RBCs in blood
– Four-chambered heart
– Larynx with a syrinx for vocalizations
– Specialized balance organ, semicircular canals
– Nictitating membrane, translucent eyelid
– Brood patch, bare belly area for egg contact
– Preen gland, uropygial gland near tail
Anatomy of chickens showing key bird features
Chickens share all the typical characteristics that make birds unique from other animals. A few examples in their anatomy:
Feathers
Chickens are covered in feathers that provide insulation, allow limited flight, and protect from water. There are soft, downy feathers close to the body and stiffer, elongated feathers on the wings used for flight.
Wings
While not the most adept fliers, chickens have modified forelimbs with longer flight feathers on the last digits that act as wings. They can flap these wings to become briefly airborne or to slow their descent when falling.
Hard eggshell
Chicken eggs have a calcified shell made of calcium carbonate crystals embedded in a protein matrix. It has tiny pores for gas exchange but otherwise provides hard protection for the developing embryo inside the egg.
Beak
Chickens have a short, pointed beak well-suited for pecking, grooming, grasping food, and other tasks. The upper and lower mandibles are covered in keratin but have no teeth.
Skeleton
A chicken’s skeleton is lightweight with some fused vertebrae, air pockets in bones, and a large keeled sternum where flight muscles attach. This provides rigid support with minimal weight.
High body temperature
Chickens maintain a normal body temperature around 41°C. They fluff up feathers or hold wings away from body to regulate heat. Their high temperature helps with eggshell formation.
Efficient gas exchange
Air sacs in a chicken’s respiratory system ventilate the lungs. Combined with a strong heart and circulation, this allows for the gas exchange needed during any strenuous activity.
Sharp vision
Chickens have large, lateral eyes that provide a wide field of vision. They can detect fast movements across a wide area, helping spot aerial and terrestrial predators. Color vision helps with feeding.
Genetics of chickens
The genetics of chickens provide further evidence that they are avian species closely related to other birds. Chickens belong to the biological order Galliformes, family Phasianidae, and genus Gallus. Some key genetic similarities confirming this relationship include:
Number of chromosomes
The chicken diploid chromosome number is 78. This is similar to other Phasianidae species:
Species | Chromosome Number |
Chicken | 78 |
Japanese quail | 78 |
Common pheasant | 80 |
Wild turkey | 80 |
DNA sequence homology
Comparing the actual DNA sequences shows substantial genetic homology between chickens and related bird groups. Chickens share over 90% of their genome with turkeys and other pheasants.
Shared genes
Chickens share many identical genes with other birds that control important functions like beak shape, feather growth, egg-laying, and more. This genetic conservation underscores their close evolutionary relationships.
Sex chromosomes
Similar to humans, male chickens are ZZ and females are ZW. Many other birds, especially raptors, share this sex chromosome system. All birds lack the X and Y system of mammals.
Behavior of chickens
The way chickens behave also aligns with typical avian traits and characteristics. Some examples:
Roosting
Chickens roost overnight on tree branches and elevated surfaces. Sleeping while perching is a behavior seen in many wild bird species.
Foraging and pecking
Chickens walk along the ground using their beak to peck and scratch in search of insects and vegetable matter. This foraging strategy is essential to the lifestyle of ground-dwelling birds.
Dust bathing
Chickens bathe in dust to clean their feathers and remove parasites. Many other bird species also maintain feather hygiene through dust bathing behaviors.
Nesting
Broody hens will stop laying eggs, pluck their belly feathers, and sit in a nest while incubating eggs. Creating nests and incubating clutches of eggs are innate in all reproductively mature female birds.
Flocking
Chickens live in social groups called flocks that usually contain a dominant male and several females. Many birds including quail, parrots, and blackbirds also form social flocks with one territorial male.
Mobbing predators
Chickens band together to chase, peck, and harass predatory animals like foxes. Mobbing is an anti-predator behavior commonly seen in wild birds that may deter predators.
Vocalizations
Chickens use a range of calls like alarm calls, food calls, and mating calls. Complex bird vocalizations are important for conveying information in many avian species.
Evolutionary origins
The evolutionary ancestry and descent of chickens falls squarely within biological classifications for birds.
Close pheasant relatives
The Red Junglefowl, Gallus gallus, found in Southeast Asia is considered the primary wild ancestor of the domestic chicken. Chickens are essentially domesticated forms of this tropical member of the pheasant family.
Diverged from theropods
Birds including chickens are descended from feathered theropod dinosaurs like Velociraptor and Microraptor during the Late Jurassic period over 150 million years ago. This gives insight into their reptilian origins.
Speciation from wild counterparts
As chickens were domesticated from junglefowl over 8000 years ago in South Asia, they became reproductively isolated from wild birds. This led to morphological and genetic divergence forming the new domesticated species.
Breed diversification
Selective breeding of chickens for different traits like plumage, comb size, egg laying, and meat production has created over 200 breeds. But they all share common ancestry from Red Junglefowl.
Scientific classification
Based on all the above evidence, chickens are classified in the following scientific taxonomy that places them with all other extant birds:
Kingdom: Animalia (animals)
Phylum: Chordata (vertebrates)
Clade: Dinosauria (dinosaurs)
Clade: Aves (birds)
Order: Galliformes
Family: Phasianidae (pheasants, partridges)
Genus: Gallus
Species: G. gallus (Red Junglefowl), G. domesticus (chicken)
This standardized biological classification confirms that chickens match the characteristics used to define avian species. They are correctly categorized within the class Aves along with sparrows, falcons, ostriches, and all other living bird types.
Conclusion
In summary, chickens clearly meet the criteria for being classified as birds based on anatomy, genetics, behavior, evolutionary history, and scientific taxonomy. While domestication has shaped some unique traits, chickens remain avian creatures closely related to pheasants like peacocks, turkeys, and junglefowl. Their fundamental features like feathers, wings, hard-shelled eggs, and others identify them as members of the class Aves. So while chickens display some unusual qualities tailored for human purposes, they still nest comfortably within the avian kingdom. From their feathered bodies to their pecking habits, chickens walk, talk, and act like a bird in nearly every way.