Flightless describes birds that cannot fly. Penguins are flightless: they waddle on land and swim powerfully through ocean waters, but they'll never soar through the sky. Ostriches, emus, and kiwis are flightless too. These birds have wings, but their wings are too small, their bodies too heavy, or their chest muscles too weak for flight.

Many flightless birds evolved on islands or in places without many predators, so they didn't need flight to escape danger. Instead, they developed other strengths. Ostriches became the fastest runners in the bird world, sprinting up to 45 miles per hour. Penguins became expert swimmers, diving hundreds of feet underwater to catch fish. The kakapo, a flightless parrot from New Zealand, became an excellent climber.

When people arrived in these isolated places, many flightless birds struggled to survive. Without the ability to fly away from new predators like cats and rats, several species went extinct, including the famous dodo bird. Scientists now work to protect remaining flightless species, understanding that these birds represent millions of years of unique evolution. Some birds, like certain breeds of chickens, were domesticated by humans thousands of years ago and lost much of their flying ability through selective breeding.