The tundra swan  

Tundra swans (Cygnus columbianus) are large, graceful birds easily identified by their stark white feathers and black bills. They are so named because they spend their summers in the tundra regions of Alaska and Canada. Tundra swans primarily feed on aquatic vegetation found in shallow water. 

Social and reproductive aspects
Tundra swans form strong, permanent, monogamous relationships. During the brief Arctic spring, breeding females build their nests out of sedge and moss, lining them with down to insulate their eggs from the cold. They usually lay from 4 to 6 creamy white eggs, which they incubate for 35 to 40 days. 

In the fall, large numbers of tundra swans migrate from the Arctic to North Carolina and other locales along the Atlantic Coast. They fly in flocks of several hundred, making mellow bugling calls to each other. Tundra swans make many stops along their migration route. Two major stopping points are the Great Lakes and the Niagara River, where some unfortunate swans get too close to the brink of the falls and are swept over it to their deaths. 
 
Predators
The closely related trumpeter swan (Cygnus buccinator) of the west coast nearly became extinct because of hunting and loss of habitat due to human encroachment. Tundra swans have escaped this fate because they breed in remote areas that are free from human contact. 

Video
Download video footage of a large flock of swans in flight. (13 seconds) 

You will need RealPlayer to view this video.  

References
Special thanks to the National Audubon Society.