Except for meteorologists, nobody's more aware than birders of the point when summer starts turning toward autumn; the shore-birds make sure of that.Schoolchildren might be reveling now in what seems like endless summer, but the shorebirds know better; they're already on their way south for the winter. At our latitude, daylight reached its maximum length-about 15 hours-at the summer solstice on June 20-21. Now the days are growing shorter. There'll be about 14 hours of daylight on Aug. 1, 13 hours on Sept. 1 and so on until late December when we'll have fewer than nine hours of daylight.

At Anchorage, Alaska, and north-the latitudes where many shorebirds nest-the shortening of the days is more dramatic: 18 hours of daylight in late June, fewer than 13 by mid-September, fewer than six in late December. No wonder shorebirds get such an early start on migration.

Area birding clubs started their shorebird migration field trips in mid-July, and more are scheduled in coming weeks. Accompanying experienced bird-ers on one of these trips can do wonders for your ability to identify shorebirds, which can be befuddling, especially in autumn, when many species no longer sport their distinctive breeding plumage.

Most confusing to most people are the "peeps": five kinds of little sandpipers that look a lot alike. Birding field guides generally separate the least, semi-palmated, Western, white-rumped and Baird's sandpipers by bill length and subtle differences in plumage, but a more helpful approach based on posture and behavior is described by Cameron Cox in the July/August issue of Birding, the magazine of the American Birding Association.

Cox separates the five species into three categories: least sand-piper (in a category by itself), "standard" (semipalmated and Western) and "long-winged" (white-rumped and Baird's). Least and Western sandpipers are usually the only peeps seen here in winter, but all may be present in late summer and fall. Cox suggests watching for the following characteristics:

o Least sandpipers, the world's smallest shorebirds, are significantly smaller than the others. Least sandpapers spread out individually along muddy edges, feeding from a crouch with their knees sharply bent and their feet planted so far forward that the birds seem to feed between their toes. They look nervous, glancing around and freezing at noises.

o "Standard" peeps, the semi-palmated and Western sand-pipers, pack together in huge flocks. They feed by dropping their necks while keeping breasts well above the surface, feet are planted well back and bills reach slightly forward.

o Semipalmateds appear to have small heads and bull necks. The legs are at the center of the body. Semipalms are aggressive, often squabbling.

o Westerns are lanky and long-legged compared to semi-palms, with heads that look too big for the body. The legs are farther back on the body than the semipalms', creating a heavy-chested appearance.

o "Long-winged" peeps, the Baird's and white-rumped sand-pipers, are usually seen in small numbers mixed with flocks of "standard" peeps. Their bodies are noticeably longer and their wings are so long that the tips extend well beyond the tail, often crossing at the rear.

o Baird's has a small head, a short bill and prominent rounded eyes that look frightened. The body appears flat and legs are short, so the bird seems to hug the ground.

o White-rumped sandpipers tilt sharply forward while feeding, and they feed quickly and aggressively. Compared to Baird's, they look bulkier and larger-headed, with a slightly more upright stance.

You can read Cox's article and see the pictures published with it by visiting www.americanbirding.org and entering "peeps" in the search box.

Frances Hamilton has written about birds in Chester County since 1968. Contact her at birdlady@birdlady.com.

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