Birds are some of natures most beautiful creatures. They have been on earth for 150 million years. Most of them fly, except for a few ones that are too large and heavy (like ostriches). Today, there are 10,000 species of birds. There are three dietary groups: carnivores, herbivores, and omnivores. Carnivores (like eagles) eat other animals. Herbivores (like cassowaries) eat only plants. Omnivores (like bluebirds) eat both plants and meat.