Gyrfalcon. This is a very rare (not quite annual) visitor to remote corners of the British Isles, and is similarly rare in California. I remember spending a week on a Scottish island where a white morph had been seen a few days before. We didn't see it during the week, and checking bird news the day after we got back.... you can guess the rest!

This Feb I went up to Oregon with another mad birder to see Falcated Duck. We tried for two different Gyrs on both days and didn't see any of them, again arriving home to emails relating how the birds had shown at point blank range...

I try to tell myself that part of the fun of birding is its unpredictability, but every time I miss a Gyr it hurts!