Golden Eagles in Alaska – More than Expected

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Yes, I know this is a juvenile Bald Eagle. For some, inexplicable reason, I don’t have a Golden Eagle image in my collection.

Due to its size, remoteness, and inaccessibility, Alaska holds its secrets close. Few places in North America hold such potential for discovery. It’s part of the reason I moved here and definitely a big part of why I stay. Every so often one of those mysteries makes itself known and yields things that we may not have been expecting.

Raptors get a lot of attention from biologists. They are ecosystem bellwethers. It was through birds like the Peregrine Falcon and Bald Eagle that we understood the devastating side effects of DDT. Too, their success depends on the abundance of prey species, so studying raptors can often provide a clue on happenings further down the chain. Despite the attention they receive, Alaska is a big enough place that new information about hawks and eagles can still emerge.

Dr. Carol McIntyre is a National Park Service biologist specializing in Golden Eagles. She’s worked on the species in Alaska for more than two decades and knows more about the state’s eagles than anyone. Over the past couple of years, she and her field team have been monitoring the migration of eagles at a new site in the eastern Alaska Range, in northern Wrangell St. Elias National Park not far from the Canadian border. What they found, during their long hours in the cold, could impact our understanding of eagle populations in the north.

The long and short of it is this: Alaska’s population of Golden Eagles may be larger, much larger, than originally estimated.

For a number of years now, McIntyre has been putting satellite transmitters on Eagles captured at various sites in Alaska. By watching their migration routes to and from the state, she realized that many birds were moving through the Alaska Range, rather than using the broad Tanana River Valley to the north of the mountains. Using that data, in 2014, they scouted potential field sites in the Mentasta Mountains.

The study area is inaccessible by car, as the only road isn’t maintained during the snowy months. So using dog sleds and snow machines, they set up count and trapping sites (really, what is more Alaskan than biologists mushing to their field sites?) and settled in for some cold days watching for migrating birds.

They found some; many, actually.

During a brief 3-day scouting trip in late March of 2014, they observed for 13 hours and counted 113 eagles. That’s about nine eagles per hour. Then in 2015 the field crew (while suffering through below zero temperatures), watched for 91 hours and counted 402 eagles.

McIntyre and her crew also spent a few days in October of 2014 determining the size of the autumn migration. Turns out it’s big, as 1364 Golden Eagles were observed during 39.4 hours of observation over 9 days. On one day, October 7, 2014, the biologists observed a whopping 568 eagles, a rate of 49 eagles per hour!

I’m a bit of a raptor nut. I really, really like seeing and observing hawks and eagles, and that number of birds, almost one per minute in the first week of October, would be something to see. It’s one of the highest count rates ever recorded for Golden Eagles. I might have to make a trip down there next fall.ak-dnp-17sep07-47

Despite the huge numbers, in her recent paper reporting the study in The Journal of Raptor Research, McIntyre suggests that their count actually under-represented the migration. Undetectable high-flying eagles, short field seasons, and limited visibility from their blinds could all lead to missed birds, perhaps lots of missed birds.

Though she doesn’t put it in these terms in the paper, the Golden Eagle migration through the Mentasta Mountains may be one of the biggest movements of the species in the western hemisphere. And no one knew about it!

That is why Alaska is so darn cool. Even big movements of birds like this can go undetected, simply because no one is out looking. And really who can blame them? McIntyre and her crew suffered through temperatures that dropped down to -25C, while camping, in snow. It isn’t exactly the kind of conditions that are going to lure recreational birders.

The size of this movement also poses a question about Alaska’s population of Golden Eagles. The numbers recorded during this study strongly suggest that it might be larger, much larger, than previous estimates; good news for Alaska’s birds. This also sheds light on migration routes, and with the increased push for renewable energy, such as wind, understanding migration pathways is extremely important to avoid turbine-bird conflicts. (Such interactions never work out very well for the birds involved.)

This work yielded big, potentially important, findings. And yet neither the field work, nor the later analyses of the data, required any high tech equipment or statistical juggling. This is why natural history matters, and why such efforts should never be denigrated as soft science, or “just natural history”. Discoveries are waiting, we just need to pay attention, document what we see, and most importantly, be there.

This post relies on information from:
McIntyre, Carol L. and Stephen B. Lewis. 2016. Observations of migrating Golden Eagles (Aquila chrysaetos) in eastern interior Alaska offer insights on population size and migration monitoring. Journal of Raptor Research 50(3): 254-264.
Thanks to Dr. Carol McIntyre for answering some questions for me for this article.