Because of their wings and the wind speed outside.
swallows
The purpose of the air sacs in a bird is to help digest food into the gizzard, and to help it breathe, and stay in the air longer and more smoothly. Hope this helps!
Birds are able to stay airborne while seemingly flying in place due to a phenomenon called "dynamic soaring." This involves the bird using the wind patterns and air currents to generate lift and maintain its position in the air without expending much energy. By skillfully maneuvering in these air currents, birds can effectively stay in one spot while in flight.
Air+Lizard= Bird
The buoyant force of air would be greatest for a hot air balloon because it relies on the principle of buoyancy to stay aloft. The heated air inside the balloon is less dense than the surrounding air, creating a greater buoyant force to lift the balloon. A bird and an airplane rely on aerodynamic lift generated by their wings to stay airborne, rather than buoyancy.
A humming bird
An Experiment on a Bird in the Air Pump was created in 1768.
15 psi
the shape of the wing is airfoil. basically this is what helps it go smoothly through air...http://amasci.com/wing/airfoil.html
No, they stay where they live.
the air-y bird
Egg + air = bird