Eagles have returned to the Nooksack in droves. This is why their future could be at risk

The number of bald eagles seen around Deming in the last 50 years has sextupled, a trend that persists all along the Nooksack River.

Past studies in the area have shown only about 100 bald eagles in an 18-mile stretch of the Nooksack River, but that number has ballooned to nearly 600, according to a soon-to-be-published study.

The independent study, titled Spatiotemporal Responses of Wintering Bald Eagles to Changes in Salmon Carcass Availability in the Pacific Northwest, was conducted by Ethan Duvall, a graduate student at Cornell University in Ithaca, New York. The study will be available through the Northwest Scientific Association.

The carcasses of chum salmon feed the eagles who have migrated to the area for winter feeding, nourishing themselves on the fish that come up the river to spawn and die.

However, a decline in chum salmon remains along the river banks may be forcing bald eagles to seek food elsewhere, according to the study. A combination of declining chum salmon numbers and climate change have caused eagles to feed on the agricultural lands around the river. Byproducts from the dairy industry and waterfowl from the area have become an increasing factor in the bald eagle diet.

Duvall spent two winters trekking along the Nooksack River, beginning the study during his time at Western Washington University. While hiking in the cold months, he counted the bald eagles in the area and monitored what they ate.

“You can see the salmon in the streams, and you can hear the eagles all around,” he said. “There’s something really special about being out there.”

Duvall could see the ebb and flow of the waters, salmon and eagles. With it, he made several observations.

Chum salmon are washing away

Duvall said there were clear connections between the availability of chum salmon remains and the response of bald eagles. One limiting factor is the amount of total salmon available, and in rivers like the Skagit, this could drive eagles to rivers with more stable salmon populations like the Nooksack.

But, this is not the most important factor. Duvall said a more “ubiquitous” concern was climate change and how that affects salmon migration and water flow.

Water on the Nooksack flows in waves, with highs around December and lows around September. Traditionally, salmon would swim and spawn during the time of higher flows.

Once the salmon swim up a river to its various tributaries and spawn, they die, leaving only their carcasses. Then, chum salmon carcasses wash onto the gravel banks when the water recedes.

Duvall said it has been a recent climate change-related phenomenon where salmon swim to spawning areas about a month early. The results cause salmon carcasses to flow away from the tributaries while the river is still in a high flow stage, leaving the bald eagles with a reduced food supply.

“Anything that alters the availability of those carcasses as a food source impacts bald eagle’s ability to survive,” he said.

Eagles still have to eat

When the bald eagles are limited on their traditional food supply, this study showed they found sustenance in nearby agricultural lands.

“A couple of eagles can knock out a whole population of whatever they go after, but they’re also incredible scavengers,” Duvall said.

As eagles leave areas around the Nooksack River, he said that the number appearing at dairy farms and sites with waterfowl “dramatically” increased.

Dairy farms act as an ideal feeding area for bald eagles. They can feed off of what Duvall described as byproducts. Typically, these byproducts include the carcasses of calves and cows but also include the afterbirth of a cow pregnancy.

“The eagles are actually benefiting from the byproducts of the dairy industry, but also, the dairy farmers seem to be benefiting from the eagles in many ways too,” Duvall said.

The carcasses and byproducts of the dairy industry are unusable to the farmers and will often be removed or composted, which costs the farmers money. Duvall said the eagles help rid the farmers of useless elements of the dairy industry and pest species.

Enjoy the eagles from a distance

Such a large increase in eagle populations allows residents in the area to enjoy sights like never before. However, watchers must be careful not to alarm the eagles and cause them to leave their feeding grounds.

“You would think that such a large bird wouldn’t care, and they would just do whatever they want, and they really do care,” Duvall said.

Keeping your distance is critical for allowing eagles to feed. When eagles are feeding on a fish carcass, they have an increased awareness of their surroundings, making them much more vulnerable to being scared off.

Duvall said an eagle that becomes scared away while feeding may not return for the rest of the day or leave the river altogether. Keeping a significant distance from the eagles and having pets on a leash can both allow the eagles to feed in peace.

Finally, Duvall said there is a major importance in preserving the habitat around the river for both the salmon and eagles. This includes supporting efforts like the Wild and Scenic Rivers Act, which would limit development and maintain a free-flowing river.

Duvall said the Skagit River, once a hub for eagle sightings, limited its chum salmon population through a dam. The resulting limited salmon population has, in turn, driven eagles from the Skagit to the Nooksack.

“(The Nooksack is) definitely a river that’s critical,” Duvall said. “Disproportionately more important for eagles than any other river in the Northwest.”

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