North America is home to an incredibly diverse range of birds, from the majestic national icon—the bald eagle—to the remarkably resilient whooping crane. More than 800 bird species occur in the United States. Some live here year-round, others migrate here seasonally, and some stop in on their migratory routes to other countries. Of these birds, dozens are listed on the U.S. endangered species list, facing threats such as climate change, habitat loss, pollution, and invasive species.

Perhaps the easiest way to identify a bird is feathers—but they share several other characteristics. Birds are vertebrates, meaning they have backbones. All female birds lay eggs, which the young develop before hatching. These animals are warm-blooded and can regulate their body temperature. All birds have wings, but not all birds use them to fly. Penguins and ostriches, for example, do not fly.