Up to 50,000 have been counted at a single location. They now exist in a semi-wild state in New Zealand and Sweden. In New Zealand they thrived so well that control was soon necessary as the birds were interfering with native species. Flocks of Black swans keep together in flight by the whistle of their wings. The birds moult only once a year and the young, as in all other species of waterfowl, leave the nest on hatching.
Swans fly and swim well.
They do not dive, but merely submerge the head and neck, sometimes also the forward part of the body, when foraging for food. By changes in their posture, these gregarious birds communicate to other members of their flock when they are about to fly. This is an important signal, for larger-bodied birds need considerable takeoff space. Thus a Black swan's flight is heralded when the bird raises its neck, smoothes its plumage and face into the wind. Swans fly with matchless blend of elegance and power.