DUCKS SAY IT with a flying V in the sky: Winter's coming. Birds on the move bring out shared wanderlust, and in warmed-up-lit-up isolation from nature, even human animals respond.

Maybe that's why life on the Atlantic flyway can be fascinating. Washington and environs are birdwatchers' heaven this time of year, when flocks migrating from Canada and New England pass through, heading on to Florida and points south.

There are all levels of appreciation. At the end of August, south-bound hummingbirds zipped through Alexandria's Dyke Marsh. On a field trip, while experienced birders discussed whether the hummingbirds were ruby-throated or rufous, a beginner was learning to discriminate between hummingbirds and bumblebees.

But we all are watchers only, of a majestic and compelling movement, of shorebirds, songbirds, hawks and swans.

The mysteries of migration are still being solved. For about 2,000 years, Aristotle's idea that birds hibernate in the winter was pretty much accepted. And when, abruptly in falltime, yesterday's birds disappeared and what was actually a different species appeared in their place, well, Aristotle said the birds had changed into winter plumage.

We now know they travel, but we don't always know where they're going, or how long it takes them to get there. One of the quickest known trips made by a bird was by a lesser yellowlegs, banded on the Massachusetts coast one Aug. 28 and, unfortunately for the bird, shot six days later. On the island of Martinique. That's 1,930 miles, or 322 miles a day if it flew nonstop. But there's no way of telling how long the shorebird had been in Martinique before its demise.

This time of year, at about sunset, if you're near especially large chimneys - and there are several in the area of the Smithsonian - you can see swifts, looking for all the world like a troop of flying cigars, circling into a funnel-shape overhead, and swooping inside. A chimney's kind of hotel for them; the next night the boarders change.

But, blast it, where do they go in the morning? Chandler S. Robbins, a Fish and Wildlife Service biologist who specializes in migratory birds and habitats, can only say, "Down to South America somewhere."

Robbins tells this story. Once, at the headwaters of the Amazon in eastern Peru, a missionary found an Indian wearing a necklace made of the harmless bands curious ornithologists are wont to attach to birds' legs. The bands, it was later discovered, had been put on chimney swifts in the eastern United States. That was 25 years ago, and since then, despite all the banding of new swifts, not even a postcard.

Then to baffle us further, the lighterweight birds, like songbirds, travel at night. (They eat during the day.) You can catch a glimpse of them as they migrate. If you're watching the moon with a telescope, you'll see them flying through the moonlight. In fact, some people in days of yore, disagreeing with Aristotle, believed birds went to the moon in winter.

If you want to see these birds in the daylight hours, the early morning is their active time. With the help of binoculars and a field guide, you may be able to see and identify as many as ten different varieties of warbler in treetops. Warblers, vireos, thrushes: These songbirds are migrating now, and mid-September is the peak time.

Songbirds like wooded areas, especially Rock Creek Park, the National Arboretum, Glover-Archbold Park (44th Street and Reservoir Road NW), the entire stretch of the C&O canal (try the Seneca area, and Hughes Hollow, near Hughes Road and Old River Road), and the Shenandoah Valley.

The most highly recommended place to see songbirds - and practically any other kind of local migrant - is Cape May Point, N.J. Lola Oberman, who's Maryland Ornithological Society's field trip coordinator and a columnist for the Audubon Naturalist News, call it "THE exciting place. If you've had bad weather, they don't fly for awhile. Then after it clears, you'll see layer on layer - huge flocks of everything. You can see 100,000 swallows at once leaving Cape May."

Why do all these birds congregate there? Robbins says it all has to do with the west wind. Migration weather means clearing conditions and northwest wind. When birds are migrating at night, they can't see so well where they're going, and the westerly component of the wind pushes them eastward. In the morning, as it gets light, they find they are over water and fly to the first land they see. It's especially true at Cape May, where there's water all around: the Atlantic to the east, the Delaware Bay to the south and the broad Delaware River to the west.

Land birds won't survive if they get lost over the ocean. But there are some birds, the pelagic species, who spend most of their lives on the water, and come to land only at breeding time, to nest.

At the coast, 97 percent of the migrating birds are young ones - as compared to 60 to 70 percent in the usual migrating group. Adults just navigate better, and compensate for the westerly component in the wind.

As for birds you usually associate with the beach, sandpipers and plovers, migration has been going on since July, and will continue 'til it's just a trickle in November. You find them in tidal marshes: shallow water with muddy or sandy shores. "A lot of them go to South America," Robbins says, "but a half dozen species winter along the coast. As winter approaches, there are gradually fewer and fewer, and they become more concentrated in places like Chincoteague." They may winter over in Cape Charles, the southern tip of the Delmarva Peninsula.

These birds are terribly social and you'll see them flocking together now at Assateague, along the Delaware coast at Bombay Hook National Wildlife Refuge, Little Creek State Park and Cape Henlopen, and at Sandy Point State Park in Maryland.

You'll even see them visiting farther inland, along the Potomac, at Andrews Air Force Base after a good rain, and on a privately-owned fish hatchery near Sugar Loaf mountain in upper Montgomery County, called Lily Pons. Robbins says an unusual number and variety of shorebirds are attracted to Lily Pons because the hatchery rotate ponds, draining them serially, thereby creating the unvegetated, muddy areas shorebirds need for feeding.

As songbirds and shorebirds move out, bigger birds are flying through that don't need the cover of night to migrate safely: the hawks.

Besides being awesome, hawks have aplomb. On their way from Eastern Canada, they head to the Appalachians and take advantage of the topography by riding updrafts along the ridges. Donald Messersmith, who's an ornithologist as well as professor of entomology at the University of Maryland, says Hawk Mountain, about 15 miles north Reading, Pa., is the best place to see them soar. "The hawks set their wings and ride for miles without flapping them.They come in low and you can see them for miles."

Other good locations are Waggoner's Gap, Pa., (20 miles west of Harrisburg), any commanding view along the Blue Ridge Parkway in the Shenandoah, and, closer to home, Monument Knob in Frederick County's Washington Monument State Park.

Hawks will be moving through 'til November, but different ones pass at different times. The peak of broadwing migration at Hawk Mountain is between Sept. 16 and 23; you're likely to see 5,000 in one day from that bare mountaintop. The sharpshinned move from the end of September to mid-October; the redtails, October and into November.

It isn't possible to predict exact dates, but you can tell something about flight schedules if you pay attention to weather forecasts. The biggest groups of birds arrive a day or two after a cold front has passed through: They virtually ride in on it.

Last, just in time for Thanksgiving, arrive the waterfowl - ducks and geese, followed by whistling swans.

In the marshes of Chincoteague, Canada geese and ducks - mallards, black ducks, gadwalls, green-winged teals and American widgeons - will be wintering over. They congregate, too, at Bombay Hook (last year, Canada geese numbers peaked early there, over 50,000 by mid-October) and all along the eastern shore of the Chesapeake Bay. Remington Farms near Chestertown, Md., is noted for flocks of Canada geese, and Kent Island is winter headquarters for whistling swans and Canvasback ducks.

The Riviera of duckdom is Blackwater National Wildlife Refuge, in the marsh country below Cambridge, Md., where it's possible to see 15 species of waterfowl or more a day. Most common and most conspicuous are Canada geese - 85,000 at their peak, the second week in November last year. From time to time, a large flock of geese take off for nearby cornfields to feed.

Blackwater's especially good to see in hunting season, says Robbins. "It's closed to hunters, and so the ducks congregate there. After hunting season is over, the ducks move out to other areas and become more dispersed. Yes, they know. Let's say the survivors know."