If a birds wings are hollow how does that affect its flying?

Hollow bird bones make flying less energetically expensive. When a bird flaps its wings, it must overcome both the force of gravity and the resistance of the air. The lighter the bird's bones, the less energy it must expend to achieve flight.

In addition, hollow bones help to insulate birds, keeping them warm during flight. Birds can lose heat rapidly through their wings, so having hollow bones helps to prevent them from losing too much heat.

Finally, hollow bones provide buoyancy, which helps birds to stay afloat in the air. This is especially important for large birds, such as eagles and vultures, which may have to stay in the air for long periods of time.