On a clear day, the view from atop Hawk Mountain stretches for more than fifty miles... all the way to the Poconos, or the Lehigh Valley. But on this particularly hazy Saturday afternoon, bird-watchers are pushing binoculars and telescopes to their limits.

"Well, we're making them out there, they're coming in. It's like you just gotta wait til they get a little closer than what they typically do. They've been popping out of clouds and haze all day for us."

Doug Wood is a volunteer at Hawk Mountain. This afternoon, he's the official bird counter.

"We're basically taking a lot of field information. Wnd, weather, temperature, cloud cover, wind direction. And then we're basically monitoring the birds' species, age, sex, and recording it every hour."

Researchers at Hawk Mountain have been keeping records of osprey and other migratory raptors for more than seventy years — making it the oldest monitoring station in the world.

In the early twentieth century, hunters would shoot thousands of the birds from the mountainside each year. In 1934, conservationist Rosalie Edge purchased a plot of land to create a bird sanctuary — which has grown to a 2,400-acre destination for bird lovers, scientists, and students.

Matt Wong came all the way from New Zealand to study at the sanctuary.

"Hawk Mountain is internationally renowned as a hawk watch site. And also a place where big research actually happens. Now, not many of the locals around Pennsylvania actually realize this, but it's actually huge on the international scene. It's world recognized, and that's one of the reasons why I came here.

New Zealand only has two species of raptors, the New Zealand Falcon and the Australasian Harrier.

But even with dozens of species populating North America, many people still think of them as strangers... or sometimes even as monsters.

" I still get, amazingly to me, a lot of people that think that these birds are out to get us."

Volunteer Bob Owens has spent the last 20 years doing education programs at Hawk Mountain.

"If you intrude into their territory when they have young in the nest, yeah, they're probably going to chase you. As far as them killing babies and taking them from baby carriages, this is all old wives tails. This just does not happen."

Owens runs a farm in Bucks County... where he says hawks and barn owls help keep rodents under control. But in a larger sense, Owens says there's a lot people can learn from these birds.

"Any three and a half pound bird that can apply four hundred pounds of pressure with its talons is built to do what they're doing. They are at the top of the food chain. And that's the other big thing that it shows us. It just opens a door here as to all the reasons the birds are either dropping or rising in population. What are we doing?"

Owens says in the 70 years researchers at Hawk Mountain have been counting birds, they've seen populations rise and fall. Although hawks and eagles are hardy predators, Owens says birds can fall victim to environmental change.

Keith Bildstein is the sanctuary's director of conservation programs. He says raptors work like "canaries in coal mines," — for the world at large.

"Birds of prey are excellent biological indicators. In the middle of the last century they told us that we were having a problem with our misuse of organochlorine pesticides, specifically DDT. Today, they're leading us in explorations of the spread of West Nile Virus."

Bildstein says because raptors are at the top of the food chain, when their numbers fall it's a pretty good sign that their food source is dwindling, their habitat could be disappearing, or air quality might be suffering.

But for most of Hawk Mountain's visitors, the birds are more than barometers of a healthy ecosystem. They're beautiful creatures... especially when viewed from a great height.

"These birds are just so majestic. And the other thing is that they go so far. You know, some of these birds are going to South America!"

Judy Higgs first climbed the mountain in 1970, when she was a student at nearby Kutztown University. Before moving out of state, Higgs used to come to Hawk Mountain daily... she stills visits up on weekends whenever she can.

" I used to do work in the morning, come here in the afternoon, go home, and finish my work at night so I could be here."

By day's end, Higgs and her fellow birdwatchers count more than 600 raptors... Over the next few months, as many as 70,000 predatory birds, from vultures to falcons might pass by on their way to distant points.

More information and some pictures are available on the web at GreenWorks.tv. I'm Brad Linder.