Wednesday, November 14, 2012

Meet the eagles!

Get ready to meet our eagles! We captured five eagles on the Chilkat River this year, and we'll be tracking their movements from now until the transmitters fail (or fall off, or the eagle... dare I say it?... dies)(Which is not going to happen. I hope.). If all goes as planned, we'll see the daily movement patterns of these eagles for at least the next three years! We can't wait to see where they spend their time during different parts of the year.

We captured our first eagle late morning on Saturday, November 3rd, using the ballistic net. A sick juvenile eagle couldn't resist the free food in front of our net launcher, and began to feed. An adult eagle came and roused the juvenile off the bait, and fed in its place. The result? We netted our first bird, a healthy, hefty adult female!

4N, just after being freed from the net



We're identifying our eagles by the green, alphanumeric leg bands we fitted to the birds. The numbers are easy to remember and keep track of, and, if you ever find yourself in the Chilkat Valley in autumn, you can look for them, too! This female received green color band 4N.

There's really no way to tell how old an adult eagle is, beyond the fact that it is at least five years of age. 4N still had some pale brown streaks in a few of her head and tail feathers, so we suspect she's still pretty young, between 5 and 7 years old or so. She weighed 6.4 kg (~14 lbs).

4N, following her release

The second day of captures resulted in two birds. The first eagle we caught on Sunday was captured late morning on a perch snare. A young male, this eagle received green color band 2Z.

2Z, with his transmitter fitted
2Z weighed 4.2 kg (~9 lbs). With his mottled feather patterns, we know he's an immature bird (subadult). Based on the molting pattern of his head and tail feathers, we think he's around 3 years old.

Yiwei and 2Z during processing
The rest of the day passed by uneventfully. Just before dark, we had to call it quits for the day, and walked out on the river flats to disarm our snares and collect the ballistic net. While walking out to take down the final perch snare, Steve and Rachel noticed an adult bird sitting right on top of it. After exchanging comments about how smug the eagle looked sitting on the snare as if he owned it, they walked toward it to flush it away, only to find that it had been caught! Although it had only perched there a few minutes beforehand, it was so calm that no one realized it had been snared. It's likely the eagle didn't even notice the snare until Steve and Rachel approached it and it tried to fly away... and couldn't.

That eagle received leg band 3C. 3C is an adult male. Since we caught 3C unexpectedly at the end of the day, we had to do the processing as quickly as possible, in order to release him before dark. As a result, we only have a couple pictures of him.

3C during processing
3C weighed 4.9 kg (~11 lbs). As an adult, we have no way of knowing his exact age, but he is at least five years old. 3C is the one bird that managed to get hold of us while processing-- he grabbed Taal's coat through the leather boot during handling, and we had to pry his talons out. Luckily for Taal, 3C only managed to grab leather and wool, not skin!

Early the next morning, not too long after dawn, we captured our fourth bird, again on a perch snare. Another adult female, this bird received band number 3E. She was the largest bird we captured, at 6.5 kg (just over 14 lbs).

Dr. Ford shows us the inside of 3E's mouth

Our fifth and final eagle capture came the following day, in early morning. An injured eagle began feeding on the chum carcass set in front of our ballistic net. This attracted the attention of two healthy adult eagles and a healthy subadult. Although they were suspicious, when they saw the injured eagle feeding, they couldn't resist going in for a bite. The injured eagle left, and both healthy adults went in to feed. The subadult eagle roused one of the adults off. Then the remaining adult and the subadult began to alternately feed before we fired off the net. The adult had just enough time to escape, flying out under the back of the net, but the subadult got caught up and was captured.

Measurements indicate this bird is female, and she was fitted with leg band 4P. Her molting patterns suggest she's a little younger, probably only 2 years old. Eagles are full grown within their first year, though, so she's still a big bird! She weighed in at 6.3 kg (just under 14 lbs).

Steve Lewis with 4P
The final tally for this year's capture season is 5 eagles: 3 females (2 adults, 1 subadult), and 2 males (1 adult, 1 subadult). We'll keep tabs on these birds' movements throughout the year. Next year, we hope to put out more tags, but we'll have to generate a lot of funding to do so. The satellite transmitters and data access fees cost around $7000 each. We'd love to have 25-30 eagles, total, from the Chilkat congregation tagged with satellite transmitters, so we really need to work hard to find funding to support the rest of this study!

In the coming weeks and months, we'll post updates on how our birds are doing and where they've been moving, particularly if they migrate southward for the winter. Stay tuned!

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