Why can birds fly?

Birds have wings shaped a special way, flat underneath and curved on top. When they push through the air, that shape sweeps the air downward behind the wing, and the air pushes the wing right back up. Their bones are hollow and their feathers are super light, so the air can carry them. Eagles barely flap at all — they spread their wings and ride the warm air that rises off the ground.

Glossed over 'lift', 'airfoil', and the difference between flapping flight and gliding. The 'flat underneath, curved on top' framing is correct but doesn't name the airfoil. Save the vocabulary for a deeper conversation, or for the kid who's seen a plane wing up close.

Bird flight relies on the wing acting as an airfoil (curved on top, flatter underneath) which produces lift when air flows around it. As the bird flaps or glides forward, the air pressure above the wing drops slightly while the pressure below pushes up; the net force is lift. The lighter the bird (hollow bones, low-density feathers, no teeth, reduced organ mass), the less lift it needs to stay aloft. Soaring birds like eagles also exploit thermals (columns of warm air rising off sun-heated ground) to gain altitude without flapping. A common shorthand attributes lift entirely to the 'longer path on top' argument, but that's incomplete: lift also requires the wing to deflect air downward, which modern aerodynamics considers the more accurate framing.