Even in sparse, January garb, the river is lovely-ebbing, flooding, meandering between shores of unbroken pine and hardwood, splashed by mistletoe and holly in full berry. But the real show's about to begin.

As the sun lowers into the wooded swamps on the far bank, there comes a far-off hallooing, yodeling, piping, closing fast, the purest, wildest music of the winter Chesapeake. Flight after flight of tundra swans are on the move seeking refuge here for their nightly rest.

One of the world's largest waterfowl, weighing up to 20 pounds, around 20,000 of the swans migrate to the Chesapeake each autumn from as far off as Alaska's North Slope and the Yukon Territories. One marvels at their 8,000-mile annual round trip, wondering that they know no better winter waters in all that way.

They glide into the darkening river corridor in small groups, loose family associations consisting of mated adults, a few "teenagers" who won't form their own pairs for a few years, and one or two cygnets, feathers still slightly gray, feet and legs still pinkish instead of the adults' black. Only six months ago, the cygnets were still eggs in nests across the Arctic tundra.

As the swans touch down their aerodynamic flight lines begin to reshape, sinuous and fluid as the reptiles from which they descended-necks arch, breasts thrust forward, big paddle-feet swing down, 7-foot wings cup and curve and brake. Sunset sparkles on the wake they create as they touch down for the night.

From November until they leave for the far North in March, anywhere from a few hundred to more than a thousand wild swans turn the mile or so of river here on Maryland's Marshy Hope Creek into one of the Bay's most singular natural spectacles.

Being here as darkness falls is as much an auditory experience as a visual one. Relatively silent as they feed in fields and loaf on open Bay waters during the daytime, the swans get downright social at night, gabbling, purring, woohooing, squealing (the cygnets)...the sounds a 4-foot windpipe can produce are astounding.

Often, their conversations blend with the raucous honking of Canada and snow geese, the sassy quacking of mallards, with overtones of barred owls hooting back in the swamp, as well as the cries of several bald eagles who also hang out here in winter.

The assemblage of winter fowl is spectacular, but more profound is why they are drawn here. It has much to do with the large, undeveloped blocks of forest. One must walk in through woods for more than a mile to reach the river on one bank. The tidal swamps of maple, ash and gum along the opposite shore are impenetrable.

A few plane rides around the Chesapeake region will quickly confirm how rare such sanctuary-quality shoreline is, especially anywhere near the open tidal waters and agricultural fields where swans and geese feed.

While forests across the Chesapeake's six-state, 64,000-square-mile watershed are large-about 60 percent of the watershed-and fairly stable, the big picture is misleading. Forests closer to the Bay cover less than a third of the landscape, and are rapidly declining or becoming fragmented by development.

It was the swans' good fortune, and ours, that in 1999 Maryland's government and the private Conservation Fund paid $33 million to preserve forever about 58,000 acres of forest-about 1 percent of Maryland. This "Chesapeake Forest," as it is called, included big swaths along the Marshy Hope and the Nanticoke into which it drains. Delaware, which has about two-thirds of the rivers' drainage basin, protected another 9,000 acres of Chesapeake Forest.

That purchase, for about $275 an acre, was touted at the time as achieving a number of important goals-protecting commercial forestry (on about half of the land), buffering Bay rivers against polluted runoff and providing hunting and recreational opportunities for the future.

Equally important, I'd argue, is perpetuating the winter concerts of the swans.