An Eye Out For Hawks Scientists And Amateur Ornithologists Study The Migration Of Raptors From A Unique Aerie In Berks County.

KEMPTON, Pa. — Where did the hawks go?

For decades, each fall, tens of thousands of broad-winged hawks soared past Hawk Mountain Sanctuary en route to their winter nesting grounds in South America. Also for decades, birdwatchers enthralled by these graceful raptors have trekked up a rocky trail to one of the best hawk-watching sites in North America.

But each year, fewer and fewer hawks have flown by. The number of broad- wings peaked at more than 29,000 in 1978, but by the early 1990s their numbers had fallen to less than 5,000 a year.

Have pesticides been killing them off?

Are South American hunters shooting them?

Is it an avian disease? Acid rain?

Nobody knew for sure until one hawk watcher, Kirk Moulton, decided to test a theory that maybe the broad-wings had just changed their migration route. (Other hawk species didn't seem to be suffering such a decline.)

Last month, working with the sanctuary's staff, Moulton organized an 11-day hawk watch. Amateur birdwatchers were assigned to perches every five miles

from the Appalachian Mountains to the Delaware River. By the time the study was completed on Sept. 20, several hundred amateur ornithologists had participated.

Most scientists had thought the broad-winged hawks flew south along narrow routes that closely followed the ridges of the Appalachians. But Moulton's team found that their flight path was much wider, extending from the mountains to the Delaware River.

"We're delighted," Moulton said. "This is the first time anybody has actually proved that their migratory pathway has changed."

Moulton's discovery is a prime example of the research done by the Hawk Mountain Sanctuary Association, a nonprofit research, conservation and education group.

Since the sanctuary was founded 60 years ago, its members have compiled the longest, most detailed migratory record of hawks, eagles, falcons and other raptors of any institution on Earth.

Based on the organization's records, more than 120 scientific papers about migratory birds have been published. Many of the nation's leading naturalists, including Roger Tory Peterson, the dean of American birding, have spent time here. Rachel Carson used Hawk Mountain statistics to write her classic book, Silent Spring, which documented the impact of pesticides on birds and other wildlife.