Question

Why do birds fly high in the sky not cast their shadows

Answer 1

The umbra is absent and the penumbra is too large and too faint that it is not visible. When the bird flies high in the sky, the distance between the bird body and the surface of the earth is very large. Even if the light is obstructed by the bird body it will not be able to cast the shadow due to such large distance. Therefore, birds flying high in the sky do not cast their shadows.