Were they small songbirds? it's not clear from your description if you saw them afloat or on land, and how big they are. If they're songbirds that were hanging out largely on the ground, they may well have been snow buntings. I saw a flock in Cabbagetown about three weeks ago, in a birch tree-- they always flock, and are a striking black and white at a distance, with a chestnut wash (esp in the sides) becoming clearer closer in and in good light. They are Arctic breeders that often come this far south, especially in cold weather.