On a sunny day, d

The bird or an airplane flying high in the sky do not cast their shadow on the ground because they are at very high altitude due to which the ground which acts as screen for the shadow is far away and in absence of the screen the shadow cannot be formed.

When they are at some lower height or near to the ground than we can see their shadow because ground acts as screen there and we see their shadow the ground. The figure below shows the shadow of bird flying near to the ground.