How do birds fly?

A bird's bones are hollow and light inside. This is why birds can lift into the air easily. The top of a wing is curved, and the bottom is flat. When a bird flaps its wing, air flows differently over the top than under the bottom. This makes a force that lifts the bird up.

When birds fly, they beat their wings down hard. This movement lifts them up and pushes them forward at the same time. When they lift their wings back up, they make them smaller so there is less air pushing against them.

Birds have very strong chest muscles. These muscles give the power needed to flap the wings. Their feathers are also light, but they hold the air well too.

Some birds can fly without flapping their wings at all. Eagles, for example, glide by using warm currents of air.