Late yesterday afternoon as it was getting dark I ventured past a few favorite winter locations to check on the current status of the Snoqualmie Valley swan population. I found a nice group of 40-50 Trumpeter Swans in a field halfway between Duvall and Carnation. Nice! But...wait...5 minutes with the binoculars after I photographed a couple of them closer to me revealed a nice surprise: one of the 50 was a Tundra Swan! Alas...how to tell the difference!?!?! It is much easier like this when they are mixed, as the Trumpters are larger. But alone it is a "who know??!!" guess...ah, but not maybe so. I look for my one easier trait to see if they are Trumpeter Swans: a somewhat flat portion on their head heading from the bill up to the top of the head. Tundra Swans are more rounded. There are other things too, like a thicker bill, more black/wider bill, and more deeply black around the eyes. But instead of me trying to explain these things that you can only really "tell" by seeing, one good source is David Sibley and a website page dedicated to this exact mystery! Go here to the Sibley Guide and have fun! Let me know if you see more Tundra Swans around here - they are more common in SW Washington and Eastern Washington in winter, unlike our areas northward on the west side of the Cascades up into B.C. which are almost all Trumpeter Swans. 
Fun stuff trying to be a biologist!
(photos: Trumpeter Swan in near dark of sunset --- no, I didn't get the Tundra Swan as it was at least 200' away from me and these were only about 50' away! But I'll keep trying! The swans shown below on Jan 25th from Ridgefield NWR are Tundra Swans, for what it is worth....)
