Bald eagles adapt after climate change decimates salmon: Experts
Bald eagles congregate along waterways in the northwest corner of Washington state for long periods of winter, taking advantage of abundant food and spawning salmon that die and wash ashore. But climate change is forcing eagles to adapt.
Now the dead salmon have largely disappeared – completely wiped out by climate change. But the apex predators have moved on to eating on the farm.
They switched from feeding along the river to patrolling farms – feasting on dairy farm waste not dead salmon. Now their favorite foods are cow placenta and dead calves.
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What’s Happening to Bald Eagles:
What did eagles eat before?
Salmon die after spawning, providing a rich source of nutrients to local ecosystems, including the bald. eagles.
- How it worked: The dead salmon gently washed up on the riverbanks for the hunting eagles.
- What is happening now?: Salmon carcasses are being washed downstream by high winter waters.
- Why? Salmon spawn earlier because the rivers and waters have warmed. Winter waters also occur at other times.
- The final result: Dead salmon are no longer an easy food source for eagles.
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Many eagles relied on salmon for food
“The river eagle community is truly one of the greatest things about living here,” said Ethan Duvall, who has been studying them for more than a decade.
“On the peak day, we spotted over 600 eagles in one stretch of the Nooksack River. It was really cool,” says Ph.D. Duval. candidate in ecology and evolutionary biology at Cornell University. He recently co-authored an article on the phenomenon in Ecosphere.
What happened when the salmon stock was swept away?
The number of eagles along the river began to decrease.
As he researched, Duvall found that climate change was changing things. Historically, salmon would swim upriver during high water events and then spawn after the waters receded.
But we do not say “eagle-eyed” in the sense of observant. With so little salmon to eat, the eagles looked for other food and found it in the rich dairy farms of western Washington and southern British Columbia, Canada.
Dairy cattle always calve, meaning local farmers have always had placentas and stillborn calves. When they were released into the field, the eagles found a new feasting ground.
“Between nocturnal coyotes and diurnal eagles, carcass dissection takes about 48 hours,” said Karen Steensma, an author of the paper and a professor of biology at Trinity Western University in Langley, British Columbia.
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“I’ve heard people talk about 50 large predators in their fields. It’s a really efficient cleanup,” said Steensma, who studies wildlife interactions with agriculture and whose family owns a small dairy farm on the Washington side of the border.
Is it beneficial for farmers?
This made sense for local dairies, which had little waste to compost or took away. In addition, eagles stop and eat birds and rodents that may contaminate or eat food caches.
It helps eagles because it provides an important and abundant food source during the peak of winter when survival is most difficult for them and they typically have the highest mortality rates.
A stillborn calf can weigh up to 90 pounds if the placenta is around 20 years old. “It’s a significant amount of food,” Steensma said.
“This research gives me hope,” said Duvall, “that, moving forward, farmers, wildlife managers and conservationists can work together to think critically about how to maximize the benefits for people and wildlife in the spaces they share.”
The paper was published in the journal Ecosphere in March.