Some blackbirds have found city living so much fun (the theater scene! the restaurants!) that they have given up migrating south for the winter. Cities are usually warmer than the surrounding country, with lots of discarded food for the birds to scavenge. If the non-migratory birds start breeding sooner, the two populations may eventually split into different species. Even if we can't predict what fully urban blackbirds will look like, we do know that they will likely be smarter than their country counterparts.
Photo via TarikB