Bald eagles have long congregated in winter along waterways in the northwest corner of Washington state, enjoying the plentiful food as chum salmon spawned, died and were swept along the banks. waterways. But climate change is forcing eagles to adapt.
Now these dead the salmon have mostly disappeared – literally washed away by the effects of climate change. But top predators have turned to on-farm meals.
They went from feeding along rivers to patrolling farms – feasting on the rejects from dairy farms rather than dead salmon. Now their favorite foods are cow placentas and stillborn calves.
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Here’s what happens to bald eagles:
What did bald eagles eat before?
Salmon die after spawning, providing a rich source of food and nutrients for local ecosystems, including bats Eagles.
- How it worked before: Dead salmon washed up gently on the banks of the river for the greedy eagles.
- what happens now: Salmon carcasses are carried downstream by winter high water.
- For what? Salmon are spawning earlier because the rivers and streams have warmed up. And winter high water also occurs at a different time.
- The final result: Dead salmon are no longer an easy food source for bald eagles.
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Many eagles relied on salmon for food
“Eagle congregations along the rivers are really one of the coolest things to experience here,” said Ethan Duvall, who has studied them for more than a decade.
“On a peak day we saw over 600 eagles on a stretch of the Nooksack River. It was absolutely amazing,” said Duval, a Ph.D. candidate in ecology and evolutionary biology at Cornell University. He is co-author of a recent article on the phenomenon in the journal Ecosphere.
What happened when the salmon supply was swept away?
The number of eagles along the river began to drop.
When he investigated, Duvall found that climate change was changing things. Historically, chum salmon sailed upstream during floods and then spawned after the waters receded.
But it’s not for nothing that we use “eagle-eyed” to mean observer. With less salmon to eat, the eagles sought other foods and found them on the wealthy dairy farms of western Washington and southern British Columbia in Canada.
Dairy cows are still calving, which means local farmers still had placentas and stillborn calves to dispose of. When they deployed them in their fields, the eagles discovered a new feasting ground.
“The breakdown of a carcass occurs in about 48 hours between coyotes arriving at night and eagles during the day,” said Karen Steensma, author of the paper and professor of biology at Trinity Western University in Langley, in British Columbia.
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“I’ve heard people talk about 50 large raptors in their fields. It’s a really effective cleanup,” said Steensma, who studies wildlife interactions with agriculture and whose family owns a small dairy farm in the Washington side of the border.
Is it also good for farmers?
It’s a win-win for local dairies, which have less waste to compost or take away. Additionally, eagles deter and eat birds and rodents that may enter and contaminate or eat food stores.
It helps eagles because it provides a large and plentiful food source during the height of winter when it is most difficult for them to survive and they usually have the highest mortality rates.
A stillborn calf can weigh up to 90 pounds while a placenta weighs around 20. “That’s a significant amount of food,” Steensma said.
“This study gives me hope,” Duvall said, “in the future, farmers, wildlife managers and conservationists can come together to think critically about how to maximize the benefits to people and wildlife in the spaces they share”.
The article was published in March in the journal Ecosphere.