Falling salmon leads eagles to hunt for food in Washington’s farming district
Every winter, recently spawned salmon carcasses are pulled out hundreds of bald eagles Rivers from Western North America to the Pacific Northwest look for foodHowever, as salmon populations decline due to climate change and other human-caused stressors, eagles may struggle to survive this dwindling food source. A new study finds that eagles are relocating to other habitats — including agricultural sites such as dairy farms — in search of food.
A bald eagle flies over a partially frozen lake in winter in search of food. Photo: Jim Pico/Frick
This isn’t the first time eagles have been threatened by human activity. In the mid-20th century, the pesticide DDT destroyed bald eagles in the United States. The chemical builds up in the bodies of predatory birds such as eagles, causing the eggshells of the chicks to thin, greatly reducing their reproductive success.By the 1950s, bald eagles had Washington is wiped out And almost left America.However, in 1972, DDT was banned after the book was published. silent spring Author Rachel Carson brings awareness to the devastating impact of DDT on wildlife, and eagles can comebackThe bald eagle was removed from the federal Endangered Species Act in 2007, and a decade later from Washington State’s list of protected species — a huge success story for conservationists and eagles alike.
Now, birds face new threats.
Condor seasonal migration Look for food – especially their favorite salmon. Some eagles do not migrate at all if they continue to get food during the cold winter, while others migrate to open water in winter when lakes and streams freeze.Northwest Washington, with its free-flowing rivers and salmon-filled high seas, has historically used to be a refuge For these eagles that migrate in winter. Adult salmon reach the end of their lives after returning to the birth stream to reproduce. As salmon spawn each fall, thousands of carcasses litter the banks of the Washington River.
However, declining salmon supplies over the past century are now threatening these eagles and other species that have long relied on fish.climate change causes Large river flows and floods In Washington in late fall, they washed dead salmon out to sea before they were eaten by eagles.In addition, many salmon populations in the area shrunk Changes to their habitat due to other anthropogenic causes, including dam and warm streams. Stream temperatures have soared in recent years Atmospheric temperatures increase as glaciers retreat and provide less cold water, and intense heat wave become more common.These changes are bad news for cold-water species like salmon experience heat stress and die When water temperatures rise too high, it’s also bad news for predators that depend on them — including bald eagles.
The Sholes Glacier on Mount Baker, which feeds the Nooksack River and cold water for salmon in summer, has been retreating rapidly over the past few decades.Photo: Jenna Travers
To understand how the foraging, migration and habitat patterns of Pacific Northwest bald eagles are changing with climate change, Dr. Ethan Duvall said. A Cornell student in the Department of Ecology and Evolution has surveyed eagles in river basins in northwest Washington state for two years and compared his data with previous papers and research. his discoveryforthcoming in Northwestern Scienceindicating that due to the effects of climate change on salmon populations, “a large fraction of aggregated eagles are redistributed [from rivers] to the agricultural area” to find other sources of food.
Duvall decided to start the research as an undergraduate at Western Washington University. In an interview with GlacierHub, he mentioned his passion for ecology and ornithology and his desire to conduct independent, relevant research as his motivation for this long-term project.During the winter months, he surveys a 30km stretch of the Nooksack River every week and compares his data with previous surveys in the same area dating back to the 1970sThis extensive dataset allowed him to understand not only current patterns of bald eagle migration and foraging, but also long-term changes caused by anthropogenic stress.
In an interview with Duvall, he explained that bald eagles in the Pacific Northwest “respond directly to the supply of salmon carcasses.” As salmon populations dwindled, eagles began to seek food in other areas, especially agricultural areas. According to the study, eagles are concentrated in the vicinity of dairy farms and duck rafts, eating cattle placenta and duck carrion.
Eagles flock to farms in response to farmers feeding them dead chickens. Photo: Dennis Jarvis /Frick
The study also revealed striking differences in eagle abundance between two different watersheds in northwestern Washington, underscoring how differences in riparian management can dramatically alter ecosystems. Eagle numbers on the Nooksack River have increased dramatically since the 1970s, while salmon are relatively healthy. However, on the neighboring Skagit River, different story“The precipitous decline in eagle populations coincides with a dramatic decline in salmon populations, primarily due to dams,” Duvall said. Eagles in the area had to migrate to the Nooksack River or to farmland near Skagit in search of food.
On eagle conservation, Duvall stressed that “we must protect our salmon populations and work to mitigate human disturbance to our rivers.” He noted that if environmental managers and conservationists do not act to address the decline of skagit salmon populations problem, then salmon and eagle populations may not persist there.As climate change worsens, more salmon will be at risk local extinction– A phenomenon in which a population no longer lives in the place where it once lived, even if it did live elsewhere. This in turn threatens eagles and people who depend on salmon for survival, cultural and economic reasons.
This research underscores the importance of addressing the ways in which humans impact rivers and species that depend on flowing, clean water in the Northwest. Without human action, bald eagles would no longer be able to rely on this part of the United States for food during the winter.
In the past, our society has saved bald eagles and other species by taking on the difficult task of ridding our economy of toxic pesticides. It remains to be seen whether we will take on the larger task of transforming our energy system away from fossil fuels, reducing warming and protecting salmon, eagles and other species threatened by climate change.
