This document discusses various aspects of birds. It covers that birds have feathers and live everywhere on Earth, making different sounds. It also notes that some birds cannot fly, like ostriches and penguins, because they are too heavy. These birds have adapted in other ways, like swimming or running. The document additionally mentions that birds can get sicknesses that cause them to lose their feathers. Finally, it states that all birds lay eggs of varying sizes to protect developing baby birds.