Why is the shadow of a bird flying high up in the sky not seen on the ground ?

When a bird or flight fly very close to the earth, The sun rays falls over them and their shadow do fall on the earth. U can see it in movies while they capture from other helicopter's or so. for example ( True Lies). When the flight or eagle gets into the clouds and fly high, the shadow falls on the clouds and not on the earth.

Its as simple as u can see ur own shadow on the floor. When a fat guy who can cover u completely stand in front of u r behind u, The shadow of yours either falls on him or hides in his shadow. hope that clarifies.