I am always in awe when I drive to a certain park and along the way, I look for this hawk perched in a tree in the distance. I can find him most of the time, given his stark white coloring, sticking out like a sore thumb. On this day, he was pretty close to the road, so I got lucky!
He is not albino in the truest sense because of his patch of coloring on the crown of his head. He also has a just few tail feathers (not visible at this angle) that are the typical rust coloring of a red-tail hawk.
Leucism (or Leukism)
Leucism is a very unusual condition whereby the pigmentation cells in an animal or bird fail to develop properly. This can result in unusual white patches appearing on the animal, or, more rarely, completely white creatures.
Albinism is a different condition. The easiest way to tell the difference between the two is that in albinism the eyes are usually pink or red, and albinism affects the entire animal, not just patches.
To see details, click on picture to enlarge.