Rheas are large, flightless birds native to South America that are closely related to ostriches and are often referred to as 'ostrich look-alikes'. They have long legs, long necks, and small heads, and are the second largest bird in the world after the ostrich. Rheas are omnivorous, eating a variety of plants, insects, and small animals. They are also known for their ability to run quickly and can reach speeds of up to 40 mph.