Boat Tailed Grackle is quite rare in NYC.
There is one currently in Central Park, which has been associating with a large flock of Common Grackles all winter, but that is the only one reported near here afaik.
Separately, there is a partly leucistic Common Grackle with a white head that is also present in the Park and these are somewhat routine.
So I'd guess this bird is probably one of those, but doubt that this photo allows a firm conclusion.