Some fun facts about birds include that not all birds fly, even though their ability to fly is one of the first things people think of when they consider birds. There are nearly 10,000 species of birds, and they are found nearly everywhere on Earth, from the Arctic to Antarctica.
Another fact about birds is that they are the only animals that have feathers, though they're not the only animals that can fly. Feathers not only allow birds to fly, but protect them from inclement weather and the sun's ultraviolet rays. They are made out of keratin, like skin, nails and fur. Bird bills are also made of keratin and come in a great variety of sizes and shapes that depend largely on the bird's diet. Birds that eat seeds tend to have heavy bills to crush them, while fish eating birds often have bills that are long and pointed.
Birds have hollow bones that help them to fly, and hummingbirds, which are the smallest birds, can fly backwards. However, hummingbirds can't walk or hop. Because they are the smallest birds, they lay the smallest eggs. Ostriches lay the largest eggs. An ostrich egg is also the largest single cell on Earth. All birds lay eggs. No bird gives birth to live young.