The fall bird migration actually begins in July. Along East Coast beaches, shorebirds that nested in the Arctic begin showing up along coastlines in mid-July. August arctic snowstorms happen, so arctic migrants fledge their young as quickly as possible to get an early start south.
Closer to home, male ruby-throated hummingbirds begin heading south in early August. Any hummers you see right now are probably migrants from farther north. Depending on the species, the fall bird migration runs from July through November (golden eagles).
The most impressive migrants are long-distance travelers. Arctic terns, for example, make a 22,000-mile round trip to and from the tip of the Americas. But advances in tracking technology have revealed other long-distance wanderers.
Sooty shearwaters, for example, roam the Pacific Ocean most of the year. One population follows a figure-eight pattern that takes them from Antarctica to the Bering Sea. Though they nest in the south Pacific, these long journeys keep the birds in areas where food is abundant.
We know about these phenomenal movements thanks to tiny geolocaters attached to captured birds. When the birds are recaptured, the data recorded by the geolocator can be downloaded and analyzed by computer.
Geolocators record a variety of information including the amount of daylight, which is used to determine latitude and longitude on a daily basis so their movements can be determined. Some units also record air and water temperature and even depths to which birds dive to feed.
Geolocator tags are used to monitor movements of everything from whales and sea turtles to fish and seals. Some units are so small they can be used to track small songbirds and even invertebrates.
Despite their virtues, geolocators have not made electronic transmitters obsolete. Satellite transmitters enabled biologists in Ohio to track migrating ospreys to their wintering grounds in the Amazon basin. And more recently biologists at the Center for Conservation Biology in Williamsburg, Virginia have made some stunning discoveries about the migration of whimbrels, a large shorebird with a long, decurved bill.
Whimbrels nest in northern Alaska and Canada and winter on the northern coast of South America. By attaching tiny satellite transmitters to 19 individuals over the last three years, biologists have discovered an unlikely migratory path.