The main characteristic of a bird is feathers. No other animal has feathers. Other important features for birds are wings and hollow bones.

Birds fly by flapping their wings and using air pressure（压力）to create lift under their wings. Just like airplanes do. The peregrine falcon is one of the fastest birds. It can reach speeds of over 100 miles per hour when diving. Feathers are important to birds because they keep them warm, help them to fly, and provide camouflage（伪装）. Hollow bones also help in flying because they help make the bird light enough to fly.

Although an important characteristic of frost birds is flying. not all birds fly. Some birds that don't fly are penguins, kiwis and ostriches. Penguins actually spend much time in the water where they are swimmers. Ostriches on the other hand are very fast runners. An ostrich can outrun a horse!

There are all sizes of birds. Hummingbirds are some of the smallest birds, while ostriches are some of the biggest. Different types of birds eat different things. Some birds feed on plants, some birds eat insects. and still others eat other, animals like fish, snakes, mice or rats. Birds are also known for their migrating（迁徙）patterns to large groups. Some birds will travel tong instances each season to stay in a climate that is good for their survival. Birds are sometimes kept as pets. The most popular birds for pets are tropical (热带的) birds like parrots. Birds also have a history of helping out humans in different tasks. They can carry messages (homing pigeons) and help hunt (falcons).

Read more about birds.

An ostrich can run as fast as 43 miles per hour and grow as tall as 9 feet.

Blue birds can't see the colour blue.

The hummingbird can fly backwards, but it can't walk.

The egg of a kiwi can weigh as much, as 20% of the mother's body weight.