http://www.birds.corn...Albinism_Leucism.html
Extract from the above:
Leucism is relatively unusual in birds, and albinism is rare. From 2000-2006, Project FeederWatch participants reported fewer than 1000 leucistic birds. Given that participants report about 5.5 million birds each season, the percentage of leucistic birds being reported is very small.
Typically birds with abnormally white feathers do not survive long because they are so much more visible to predators. Those that do survive may have trouble attracting a mate. Consequently, the mutated genes that cause albinism and leucism are less likely to be passed on to a new generation. If you are ever fortunate enough to see one of these oddly plumaged birds, consider yourself lucky!