Bird explained to kids

Birds are a group of warm-blooded vertebrates constituting the class Aves, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide and range in size from the 5 cm (2 in) bee hummingbird to the 2.75 m (9 ft) ostrich. There are about ten thousand living species, more than any other vertebrate group. Birds are the closest living relatives of crocodilians. Birds are thought to have evolved from theropod dinosaurs during the Jurassic period, between 200 and 150 million years ago. Birds have many unique internal and external characteristics that set them apart from other animals. Some of the internal characteristics of birds include a four-chambered heart, which is very efficient in distributing oxygenated blood to the rest of the body; a lightweight but strong skeleton, which helps them to fly; and feathers, which are unique to birds and give them their aerodynamic shape. External characteristics of birds include beaks and claws, which are used for feeding and perching, respectively; wings, which give them the ability to fly; and feathers, which insulate their bodies and help them to streamline their shape for flying. Birds are found on every continent, and there are even a few species that live on remote islands in the middle of the ocean. They can be found in a wide variety of habitats, from the arctic tundra to the deserts of Africa. Some species, such as the penguins of Antarctica, spend their entire lives in the water, while others, such as the weaver birds of Africa, build intricate nests in which to live and raise their young. Birds are an important part of the ecosystem, providing pollination and seed dispersal services for many plants, and food for a wide variety of animals. Humans have also long been fascinated by birds, and have kept them as pets, hunted them for food, and used their feathers for a variety of purposes.