Since all the light rays from these two birds will be entering the eye at the same angles, they would look exactly the same to you (you wouldn't be able to tell which is large and which is small, or which is close and which is far), without other information to give you a sense of how far away it is. (This is one way they made the hobbits in Lord of the Rings look small -- just had them be farther away from people than you thought they were.)
