Golden eagle!

Here are some photos from yesterday’s big golden eagle adventure; click through to see larger sizes (or click here to view them as a slideshow). As readers of Marcia’s Game News column will have just learned, the golden eagle migration last year only really got underway in late November. This year, it’s almost a month earlier. (By contrast, the autumn foliage has only now reached its peak — a good two weeks late.)

This bird was hatched this spring, probably somewhere in northern Quebec or Labrador. It was one of at least ten goldens that soared down along our ridge on the afternoon of November 3, chased and harried by a resident redtail. It came along just before dusk, dove for the bait, and was caught in a bow trap by Trish Miller of the Powermill Avian Research Center, who was staffing a blind on an almost inaccessible part of the Plummer’s Hollow property. The eagle had to spend the night in a pen in our basement, until all the scientists could assemble and get it fitted with a radio transmitter.

Todd Katzner, a scientist with the National Aviary in Pittsburgh who has extensive experience with wild eagles, was kind enough to do a short show-and-tell for us and our friends. Apparently, the white on the underside of the wings is one of the things that distinguishes a juvenile golden eagle from an adult. The talons are also a brighter yellow.

Typical golden eagle prey consists of hare-sized animals, Todd said. They can kill animals as large as a fox or a fawn, but they eat a lot of birds, too. They have no natural predators of their own.

Mouth-breathing is a sign of stress, Todd said. Fortunately, it was a crisp morning — they don’t take heat very well.

Measurements of wings, bill, etc. were taken not only for record-keeping purposes, but also to try and determine the sex of the bird. They compared their measurements to a list and determined that it was a female, as Todd had already surmised. Not having handled as many female as male golden eagles, they were surprised by how much thicker its down seemed to be. But that, in addition to its larger size, may be of adaptive benefit since the female does most of the incubating of the chicks in the first two weeks, until they become better at thermoregulating on their own.

Weighing the eagle. It took several hours to complete the measurements and fit the radio transmitter. The eagle was hooded with a knit cap for most of that time to reduce stress, though the superficial resemblance to the infamous images of Abu Ghraib inmates was a little unsettling at first. They also bound her talons with surgical gauze after Todd cut his finger on them.

Trish did much of the work, since the golden eagle study is going to be the topic of her PhD dissertation. Here, her daughter Phoebe interacts with the bird.

A soft teflon harness was sewn together on the spot and carefully worked under the feathers. They used cotton thread, with the expectation that it will rot off in a couple of years.

The radio transmitter is much lighter than it looks. If all works correctly, it will transmit the bird’s GPS coordinates to a satellite twice every minute.

This shot reminded me of a pow-wow dancer, almost. I wonder if the Indians ever captured eagles along this ridge? The eastern golden eagle is nowhere near as easy to trap as its western counterpart, and when this project got started two years ago, they had a hard time getting funding because few people thought they’d be successful. This is the first female to be fitted with a transmitter in Pennsylvania.

We all trooped back up to the capture site to release the bird. My mother was given the honor of actually tossing the bird into the air, in part perhaps because she was one of the few people present without a camera! Unfortunately, however, my reactions are slow — I didn’t get a good picture of her with the bird. Here’s the eagle seconds after release, with Bald Eagle Valley and the Allegheny Front beyond.

She flapped over into a white pine at the edge of the talus slope to groom herself. At one point, she reached around and lifted the transmitter in her beak, but then released it. It was a tense moment.

She spent four or five minutes trying to straighten her ruffled feathers and get used to the feeling of the harness against her skin and the strange new backpack. Finally, she launched herself into the air, circled low over our heads once, twice, then headed off to the south along the ridge. We were awed and humbled by the experience, and still have a bit of a hard time believing that our far-from-wild ridge twice a year becomes a highway for these archetypal denizens of the northern wilderness.

–Dave

UPDATE: Unfortunately, the transmitter failed after just a few days. But Trish told me they got some great data from the bird before that happened.