Bald eagles become farm birds thanks to climate change
Bald eagles have long congregated in winter along waterways in the northwest corner of Washington state, taking advantage of the abundant food as chum salmon spawned, died and were washed onto stream banks. But climate change is forcing the eagles to adapt.
Now, those dead salmon are mostly gone – literally swept away by the effects of climate change. But the apex predators have pivoted to in-farm dining.
They’ve transitioned from feeding along rivers to patrolling farms – feasting on dairy farm discards rather than dead salmon. Now their preferred dishes are cow placentas and stillborn calves.
What did eagles eat before?
Salmon die after they spawn, providing a rich source of food and nutrients for local ecosystems, including bald eagles.
⬤ How it used to work: Dead salmon gently washed up onto river banks for the eager eagles.
⬤ What’s happening now: The salmon carcasses are being swept downstream by winter high waters.
⬤ Why? Salmon are spawning earlier because the rivers and streams have warmed. And winter high waters are occurring at a different time too.
Many eagles counted on salmon
“The eagle congregations along the rivers are truly one of the coolest things to experience up here,” said Ethan Duvall, who’s been studying them for over a decade.
“On a peak day, we observed 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 a co-author of a recent paper about the phenomenon in the journal Ecosphere.
What happened when the salmon supply was swept away?
The number of eagles along the river started to drop.
When he investigated, Duvall found climate change was shifting things. Historically, the chum salmon would navigate upriver during the high water events and then spawn after the waters had receded.
But not for nothing do we use “eagleeyed” to mean observant. With fewer salmon to eat, the eagles looked around for other food and found it in the rich dairy farms of western Washington and southern British Columbia in Canada.
Dairy cattle are always giving birth, meaning local farmers always had placentas and still-born calves to dispose of.
When they put them out into their fields, the eagles discovered a new feasting area.
“The dismantling of a carcass occurs in about 48 hours between coyotes coming in at night and eagles during the day,” said Karen Steensma, an author of the paper and professor of biology at Trinity Western University in Langley, British Columbia.
Is it good for farmers too?
It’s a win-win for the local dairies, which have less waste to either compost or have hauled away.
In addition, the eagles deter and eat birds and rodents that might come in and contaminate or eat feed stores.
The paper published in March in the journal Ecosphere.