Hi All
The website below has a summary of the field characteristics of Mute,
Trumpeter and Tundra Swans

http://www.taiga.net/swans/swanid.html

Also see Birding, vol 26, no. 5 (Oct, 1994)

Cheers
Gail Spitler
Johnsons Landing, BC
mailto:spitler at direct.ca