Eagle tracking a success for Hawk Mountain

awk Mountain Sanctuary has been tracking migrating bald eagles since 1934. And it's safe to say that 2016 was by far the most successful year in history.

With the official migration season coming to a close on Thursday, researchers have already observed 481 bald eagles. That not only surpasses, but obliterates the previous record of 406 set in 2010.

"We've been around over 80 years. Our last record was in 2010, we had 406. Now we're hovering just under 500 - that's an amazing recovery," said Laurie Goodrich, the sanctuary's director of long-term monitoring.

The traditional migration period at Hawk Mountain runs between Aug. 15 and Dec. 15. There are two peaks. In August, birds from the south return to their homes after spending their summer in cooler temperatures. Then at the end of the season, birds from further north, as far as Canada, travel south to winter nesting locations along the Chesapeake Bay and in the Carolinas.

Some days, they'll see 10 birds. Other days, it's zero. It all depends on the weather.

Hawk Mountain sits along the Kittatinny Ridge, which separates the Appalachian Mountains from the flatter, more agricultural areas of Southeast Pennsylvania. Eagles from a wide swath of New England and Canada like the spot because they receive an extra boost beneath their wings from the wind bouncing off the mountain. Eagles are relatively large birds, and flapping those wings takes more effort than it does for other migratory birds.

"The wind, when it hits the mountain, creates an updraft. It gives them a nice buoyant wave of air where they can sail along the southwest and save energy," Goodrich said. "On windy days, you'll see them clustered along this mountain."

At one time, bald eagles were so endangered, due to the pesticide DDT, among other factors, that the count of eagles was just 13 in the mid-70s. Hawk Mountain's eagle count was cited by famous naturalist Rachel Carson in her book "Silent Spring," which helped expose the effects of DDT.

"Silent Spring" also inspired significant efforts to increase the bald eagle population. Federal and state naturalists worked hard to reintroduce the birds to the East Coast. Goodrich said those efforts are largely responsible for the recovery.

"Part of the reason we are seeing this record is because of the large-scale that's also happening in the northern states. this is all part of the recovery from '70s to now - there's been a steady increase of bald eagles," she said.

Pennsylvania's birds may not even figure into the count, because they actually don't need to migrate. The weather here is temperate enough for them to spend the entire year at their nest.

Goodrich is hoping they see a few more eagles before the year is done.

"Any windy day between now and the end of the year, it's possible to see bald eagles from our mountain top," Goodrich said.