Bird Watching: DAILY PICS VOL. 24, 1 by Resin

Resin wrote:

Quoting:The only way I know this is a Tundra Swan cygnet, is because this is one of three which always stayed close to the Tundra Swans

Look for the smaller size and shorter neck of the Tundras. They also have a slightly more rounded, less angular head, and a shorter bill.

There's a similar identification comparison over here with Whooper Swan (large, very similar to Trumpeter) and Bewick's Swan (smaller, very similar to Tundra), except Whoopers have more yellow on their bills than Bewick's do (and both have more yellow than either of yours). Pic below is Whoopers (scanned from a print, so not too good!).

Resin