Birds are bipedal, warm-blooded, egg-laying vertebrates characterized primarily by having feathers, wings (which generally enable them to fly), and hollow bones. Birds were created on the fifth day of creation, along with other "flying creatures," including insects or anything else that God deemed a flying creature. Hosea 11:11 characterizes them as timid. Birds range in size from the tiny hummingbirds to the huge Ostrich or Emu. There are about 8,800-10,200 living bird species.