They are called buffleheads just because they are., a photo by ricmcarthur on Flickr.
Supposedly,the shape of a males head is similar to an American bison.
Males are striking black-and white from a distance. A closer look at the head shows glossy green and purple setting off the striking white patch.
The Bufflehead nests almost exclusively in holes excavated by Northern Flickers and, on occasion, by Pileated Woodpeckers.
The oldest Bufflehead on record was at least 18 years and 8 months old. It was caught and re-released by a bird bander in New York in 1975.