Last week, as I traveled across the southern tier of New York, skeins of Canada geese crossed the sky from north to south. It was a vintage November day -- cold, gray, and damp.

At a rest stop near Jamestown, another flock caught my eye. But these birds were bigger and pure white. What a treat to see a flock of tundra swans. November is the best time to encounter these impressive birds as they head to wintering grounds on Chesapeake Bay.

Swans are huge all-white birds, seemingly impossible to misidentify, but clueless hunters sometimes mistake them for much smaller snow geese, which are easily recognized by their black wing tips. Tundra swans measure about 52 inches long with a 66-inch wing span and weigh about 15 pounds. Mute and trumpeter swans are larger -- 5 feet long with a wing span of about 6 1/2 feet and weighing about 23 pounds.

Mute swans, which are not mute, are the common swans of country estates, city parks and zoos. These exotic birds easily escape confinement and establish feral populations. The bright orange bill with a fleshy black knob at the base is diagnostic, and at rest, mute swans hold their long necks in a graceful S-curve.

The tundra swan, the species you're likely to see this month in the vicinity of the Three Rivers, is all white with a black bill. Many, but not all, adults have a yellow spot at the base of the bill. At rest, a tundra swan's neck is more erect than a mute's. And often a tundra swan's neck is stained a rust color from iron-containing minerals encountered while grubbing for submerged aquatic plants.

Trumpeter swans are the largest native waterfowl in North America. Though larger than tundra swans, trumpeters are visually almost identical, except that trumpeters never have a yellow spot on the bill. Like tundras, trumpeters also often have rusty stained necks. In fact, every trumpeter I've ever seen has had a rusty neck.

In flight, both tundra and trumpeter swans hold their long necks straight and outstretched. Even at a distance, their necks appear as long as their bodies.