Tundra Swans (Cygnus columbianus), formerly known as Whistling Swan, breed in the high arctic tundra and winter on lakes and estuaries in the lower US. A Eurasian subspecies, Bewick's Swan (C.c. bewickii) , occasionally shows up in North America - in fact, there was a Bewick's at Wascana Lake in Regina a few years ago which stayed long enough for most of us local birders to have a look at it.
The black bill shows a bit of yellow near the base under the eye - the amount of yellow is variable.
Juveniles/immatures have a pinkish-orange bill, outlined with black. They will lose their grey feathers at the first molt.
Overland migration is done at day or night, in long, trailing V-formations, often at very high altitudes. This flock of 200-300 individuals was at a slough near Torquay, SK, for about two weeks, resting and feeding.
Sometimes one will see swans with a pinkish or yellowish cast to their neck feathers. This is due to various minerals in the water where they have been feeding.