Jillian M. Liner, the Director of Conservation of Audubon New York, told Gothamist, “Leucistic birds do indeed show up every now and then, and can occur in a variety of bird species. Leucism is caused by defects in pigment cells and cause an almost completely white bird or a bird with patches of white. When a bird does not produce melanin at a normal level or in a normal pattern, their color patterns are referred to as being albino (white), leucistic (patches of pure white), or be diluted plumage colors.”
Liner added that it’s not “Mandarin duck-level rare,” but it’s still “kind of exciting” to see a leucistic grackle in New York.
This bird, spotted in the Ramble in Central Park, has a white head, and birders have been out there trying to spot him:
According to the Cornell Lab of Ornithology, “Common Grackles are resourceful foragers. They sometimes follow plows to catch invertebrates and mice, wade into water to catch small fish, pick leeches off the legs of turtles, steal worms from American Robins, raid nests, and kill and eat adult birds.” The male common grackle is dark, with an “iridescent blue head and bronzy body in good light,” while the female is “less glossy.”