White house sparrow

Yes, as doggie says, leucism is fairly uncommon in wild birds. It is the result of a genetic mutation, so where there's one affected bird there may be others, its relatives. Birds with the condition can survive perfectly well, although they are more vulnerable to predators as they stand out in the crowd. True albinism (pure white with red/pink eyes) is very rare in wild birds, they almost always have serious vision defects, which really hammers their chances of survival. The BTO are surveying garden birds with plumage abnormalities, if you're interested in taking part the survey is here: http://www.surveymonkey.com/s/plumagesurvey

PS Just got my copy of the spring 2013 Birds magazine and there's a lovely photo of a leucistic House Sparrow on p17 :)