I wish I knew why a sparrow will sit on a bird feeder for half an hour, but a cardinal won't stay more than half a minute.
When I saw him, he and his female mate were both right there perfectly positioned. While I grabbed the camera and changed lenses, Mrs. Cardinal took off. This was the only shot I got with the whole bird in the frame and in focus.
Now every time it snows I stalk back and forth past this window, but no more luck since then.
I posted some pics of a cardinal about a page back, and believe me I know what you mean. They are incredibly skiddish. i set up my camera on a tripod (left it on manual focus after i set it), and i hid it behind some plants and used a wireless trigger to set it off.
it took a couple days before it didn't mind the shutter noise. but those boring little sparrows aren't scared of anything.