Imagine waking up one morning able to fly like a bird, with no airplane, no engine and no one to carry you. This is only a what-if, because people cannot fly that way, so please never jump from a high place to try it. To understand what flying would take, it helps to begin with the animals that really do it. Birds fly by flapping their wings, and their wings are covered in feathers.

A bird's body is built to be light. Its feathers are made of keratin, a tough protein, and human fingernails and hair are made of a close cousin of that same material. Many birds also have hollow bones, which keep them light so they can fly. A bird's flight muscles are big chest muscles that pull the wings down, and they are anchored to a deep breastbone called the keel.

Birds with pointed wings, such as falcons and ducks, can reach tremendous speeds when they flap hard. The peregrine falcon is the fastest bird, and as of November 2026 it is the fastest animal on Earth when it dives. It dives at about 200 miles per hour (320 kilometers per hour), the fastest speed estimated for any bird. That speed belongs to the dive, not to every moment of its flying.

What holds a flying bird in the air is lift. Lift is the force that holds an airplane up, and it is made by air moving past the wings. One way to explain it is that the wing pushes air downward, a push-back described by Newton's third law of action and reaction. Lift needs motion: it comes from the difference in speed between a wing and the air, so a wing that is not moving through air makes no lift. Without air there is no lift, which means wings do not work in space.

Flapping is not the only way to stay up. Big birds such as eagles and storks have broad wings that let them soar on rising warm air, so they save the energy of flapping. The wandering albatross has the widest wings of any living bird, about 11 to 12 feet (3.4 to 3.6 meters) from tip to tip, as of November 2026, and it can stay in the air for hours while hardly flapping its wings. Flapping needs more and more energy as a bird gets bigger. Small birds such as warblers can flap fast, but heavier birds, from about the size of a small hawk, rely on soaring and gliding instead.

Birds are not the only animals that move through the air. Bats are the only mammals that can fly, and their wings are made of thin skin stretched between very long finger bones. Flying squirrels do not really fly. They glide from tree to tree, about 150 to 500 feet, using a loose flap of skin from wrists to ankles called a patagium. Pterosaurs were the first vertebrates to fly under their own power, and only birds and bats are the other flying vertebrates.

Could a person flap like a bird? A human's arm and chest muscles are not strong enough to flap wings big enough to lift a person. Because people cannot fly like birds, people invented airplanes to fly in.

Words to know

• keratin: tough protein
• keel: deep breastbone
• lift: upward push
• soar: ride rising air
• patagium: skin flap