August is the quintessence of summer on the human calendar, a month of lazy, crazy, hazy days at the beach or in the back yard. But for much of the natural world, the season already is turning.

It is not a showy change, with leaves bursting into color and flocks of squawking ducks landing on the pond. That comes later. Autumn in August is less conspicuous.

Nature is giving the signal, in the form of less and less daylight, that it is time to shut down, move on or otherwise take that next step. Although the monarch butterfly does not migrate until September, two lesser-known butterflies that make short-distance migrations -- the cloudless sulfur and common buckeye -- can be seen here, said naturalist Denise Gibbs of Black Hill Regional Park in Montgomery County.

But the most visible examples of summer's end are plants and shorebirds. Many trees and shrubs have finished this year's business and are on to next year's. They have bid adieu to summer.

"It's not so much they are getting ready for winter, but they are done for the season with their vegetative growth," said Phil Normandy, plant collections manager for Brookside Gardens in Wheaton. "They are switching from growing season -- vegetative growth -- to flower buds for next season, and fruit."

This is the source of advice from horticulturists not to prune spring-flowering shrubs and trees now. If you do, you cut off their flowering potential for next year. Wait until just after they bloom.

Normandy said berries on dogwood trees and some hollies are almost full size now, even though they have not changed color. Underground, bulbs that will bloom in the spring are sprouting roots or are about to. Above, acorns and nuts are forming in oaks and beeches.

Some of these fruits, seeds and berries will be food for passing birds. Their fall migration already is underway.

"Shorebird migration is going full blast by August, and songbird migration picks up steadily by late August," said John Bjerke, who teaches birding workshops for the Audubon Naturalist Society. "Birders recognize that the first of August for sure is the start of fall migration."

Shorebirds are small to mid-size birds with names such as plover, yellowlegs and sanderling. They feed on worms, insects and other tiny critters. They fly by night.

The Delaware Bay is the closest place to Washington to see them in large numbers. But they also frequent inland reservoirs, sewage treatment ponds, mudflats next to creeks and flooded fields and meadows. The mudflats along Hunting Creek south of Alexandria are a particularly good spot, Bjerke said.

These birds have summered in Alaska and Canada, where chicks hatched, and are headed to warm wintering grounds. The females begin heading south in July. Then the males go. The young, left to fend for themselves, don't leave until later and won't arrive in this area in large numbers until the middle of the month.

The adults that pass through this area are worn out from breeding and hungry. Their plumage is shabby, and they flit about frenetically looking for food. Bjerke said they might spend a week fattening up before heading on, sometimes flying thousands of miles in two or three days.

The young that make it here look fresher. The unanswered question about them, Bjerke said, is how they find the way. Maybe a few adults are around to help, and the birds know to follow shorelines on their way. Somehow, they make it.

Later this month, songbirds will begin coming through. Jeff Swinebroad, who teaches birding classes in the area, said they not only look duller than they did in the spring because they are not wearing their attention-getting breeding plumage but they also are not as noisy. They call to each other in a utilitarian way, but gone are the elaborate courting and turf-defending songs of spring.

-- D'Vera Cohn

The migration of shorebirds such as the piping plover, which gets into full swing this month, is among the most visible signs that summer is nearing an end.