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A jogger runs along a sandy strip where the gentle lap of waves signals the meeting of sea and shore.

Up ahead, a family of diminutive shorebirds use their black-tipped yellow bills to prove for beetles, marine worms and other tasty invertebrates churned up by waves.

This particular jogger hardly notices the small flock of plovers running back and forth on the water-washed sand. As she approaches, the birds freeze, cry out, then scatter in all directions.

As the jogger's figure fades on the horizon, the mother plover frantically herds the straying chicks, and the whole family returns to the serious business of foraging. They must eat enough to build up strength for their long journey south.

Just as the chicks settle back into their feeding routine, two people searching for shells disturb the birds again, sending them off in another panic-stricken flight.

For humans, the crowding of once-pristine North American beaches seems merely a nuisance. For a type of shorebird called the piping plover, beaches packed with sunbathers, shell seekers, joggers and Frisbee players represent a lethal hazard. New research suggests that as the number of people on the beach swells, these and other shore-birds spend more time running or flying from humans and less time eating. While sompe piping plovers can weather the loss, many others succumb to starvation.

"When you increase the number of people, the [piping plovers] spend less time foraging," says Joanna Burger, an avian biologist at Rutgers University in Piscataway, N.J. "Young birds can't spend enough time foraging to lay down enough fat before they migrate."

Some 200 bird species, including oystercathers, plovers, sandpipers, whimbrels and dowitchers, prefer beaches, mud flats, swamps, marshes or back bays along the North American coastline to inland areas. Piping plovers, Charadrius melodus, were so named for their melodious singing ability. The East Coast branch of the species nests on beaches from Maine to North Carolina in the spring and summer, heading south to wintering grounds from Florida to South America by early fall.

Piping plovers flourished along the Atlantic Coast through much of history, foraging undisturbed on vast stretches of sand. After World War II, however, human activity on the East Coast skyrocketed as developers scrambled to build condominiums, hotels and summer homes with oceanfront views. Many shorebirds deserted the prime vacation spots and moved to salt marshes or mud flats where they could forage freely.

Unfortunately, the piping plover won't feed in such muck, and thus must compete with people for space on the beach. During low tide, these birds scamper after each retreating wave, searching for bits of food in the wet sand.

Although their population once numbered in the thousands, the U.S. Fish and Wildlife Service in 1986 but the Atlantic Coast population of piping plovers on its list of threatened species. A survey conducted last year by the same agency indicated that only 739 nesting pairs remained on the East Coast -- a level that puts these birds in danger of extinction.

No one knows exactly what caused the precipitous decline, but most investigations have focused on the bird's vulnerable nesting site. The piping plover generally builds its shell-lined nest in a small depression in the sand between the dunes and the open water. Many wildlife biologists believe this practice puts the species in extreme danger from humans, who can inadvertently trample the nearly invisible, sand-colored eggs.

Burger, however, took a different tack with her plover research. Instead of focusing on nest sites, she decided to study how people affect the foraging behavior of the piping plover.

She began by observing piping plovers at several New Jersey beaches, including Brigantine Beach, a flat, sandy stretch backed by a belt of dunes, just north of Atlantic City. Starting in early May of 1985, Rutgers University graduate students walked a regular route down the beach, through the dunes and back along the bay. The students observed the birds five days a week for ten hours a day.

Whenever they found a flock of piping plovers, they stopped at a distance and watched the birds forage for a two-minute period, using binoculars to avoid frightening them. The observers then counted the number of people within 10 and 50 meters of the flock. During the two-minute study period, they used a stopwatch to note the seconds plovers spent looking for food. In addition, they noted how long the plovers exhibited alert behavior, in which the birds look up and about in response to a threat (such as an approaching human). Finally, the students recorded the time plovers spent running or flying from people.

Burger presented the New Jersey findings in the Winter 1991 JOURNAL OF COASTAL RESEARCH. "Overall, when more people were present, plovers spent more time running, flying and crouching," she told SCIENCE NEWS.

Like the human "snowbirds" who migrate to warm-weather spots with the first chill of autumn, piping plovers leave their northern breeding sites in late summer of early fall. The New Jersey study showed that people posed a problem for plovers during the breeding season; Burger wanted to find out whether human interference affected plovers who spend their winters in sunny Florida.

# posted by Medical Information : 3:09 AM