The main characteristic of a bird is feathers. No other animal has feathers. Other important features for birds are wings and hollow bones. Birds also lay eggs, like reptiles, however they are warm-blooded, like mammals.
What are Feathers?
Feathers are made of keratin. This is the same stuff that fingernails are made of. At the center of the feather is a hollow shaft called the rachis. Connected to the shaft are lots of thin branches called barbs. Off of the barbs are even smaller branches called barbules. All of these branches make a light structure that can gather air to fly.
Birds flying Source: U.S. Fish and Wildlife Service
How do birds fly?
Birds fly by flapping their wings and using air pressure to create lift under their wings. Just like airplanes do. The peregrine falcon is one of the fastest birds. It can reach speeds of well over 100 miles per hour when diving.
Feathers are important to birds because they keep them warm, help them to fly, and provide camouflage. Hollow bones also help in flying because they help make the bird light enough to fly.
Ostriches are birds that can't fly Source: U.S. Fish and Wildlife Service
Not All Birds Fly
Although an important characteristic of most birds is flying, not all birds fly. Some birds that don't fly are penguins, kiwis, and ostriches. Penguins actually spend a good portion of time in the water where they are prolific swimmers. Ostriches on the other hand are very fast runners. An ostrich can outrun a horse!
Types of Birds
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, or rodents.
Birds are also known for their massive migrating patterns. Some Birds will travel long distances 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 birds like parrots. Birds also have a history of helping out humans in various tasks. They can carry messages (homing pigeons) and help hunt (falcons).
Pair of Nene birds Source: U.S. Fish and Wildlife Service
Fun Facts 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 color blue.
The hummingbird can fly backwards, but it can't walk.
Condor shells are so thick, it can take a chick a week to break out from its shell.
The egg of a kiwi can weigh as much as 20% of the mother's body weight.
A pelican's bill can hold up to three gallons of water.