Because they can't cockatoo if they don't!
The bird's feathers .
you can tell if an animal have bilateral symmetry if you cut the animal in half, (hypothetically) and both sides are the same
If a animal has a head then its body symmetry is bilateral.
How can you identify the body symmetry of an animal
All vertebrates have bilateral symmetry. Therefore, any creature which is classified as a mammal, bird, fish, reptile or amphibian has bilateral symmetry. This means they have symmetry across one plane (known as the sagittal plane, and directly down the centre of their body), which means one side of their body approximately mirrors the other side
Symmetry in animals is something that is very important. It is a big part of classification in animals. Nearly all multi-cellular organisms exhibit one or other type of symmetry such as radial or bilateral. For more on this see the source.
Symmetry is important as it can test whether the student is alert
All vertebrates have bilateral symmetry. Therefore, any creature which is classified as a mammal, bird, fish, reptile or amphibian has bilateral symmetry. This means they have symmetry across one plane (known as the sagittal plane, and directly down the centre of their body), which means one side of their body approximately mirrors the other side
A hen is both an animal and a bird. All birds are animals. They are all part of the kingdom animalia.
Bilateral Symmetry
When it has no symmetry the object is called asymmetrical.
One animal that has radial symmetry is a sea sponge.