As a child, "The Birds" was the first terrifying movie I had seen. I found that I was most anxious when the birds were sitting still, sillouetted against a grey sky, or that horrible moment when she opens the door to find the bedroom filled with the large black birds, sitting still, until they attack.
Thanks to Mr. Hitchcook, black birds sitting still in a dimmed room are very ominous, especially at a distance. Vultures have the same effect. Guests always lean in and quietly ask, "Are they real?"
Here are some different applications of THE BIRDS and vultures. You will notice that, even in daylight, they look as if they just may take flight at any moment.