Basically unmistakable and is just what the name says: a swan with a black neck. Fairly common but sometimes local on lakes, slow-moving rivers, wetlands with open water, estuaries, and inshore coastal waters. Often in groups, locally hundreds in winter, and associates readily with Coscoroba Swan. Cygnets are pure white and soon develop a dusky neck; within a month or two after hatching they look like adults.