October 6, 2022

The decline in salmon has prompted eagles to seek food in Washington’s agricultural areas

The decline in salmon has prompted eagles to seek food in Washington’s agricultural areas

Every winter, it kills the carcasses of newly spawned salmon Hundreds of bald eagles From throughout western North America to the rivers of the Pacific Northwest in search of food. However, as salmon populations decline due to climate change and other human-induced stressors, eagles may struggle to survive on this dwindling food source. A new study has found that eagles are redistributing to other habitats to find food – including agricultural sites like dairy farms.

A bald eagle flies over a half-frozen lake in search of food during the winter. Photo: Jim Pico/Flickr

This is not the first time that eagles have been threatened by human activities. In the mid-20th century, the pesticide DDT devastated American bald eagles. The chemical accumulated in the bodies of birds of prey such as eagles, causing their eggshells to thin and significantly reducing their reproductive success rate. In the 1950s, there were bald eagles Completely disappeared from Washington And it’s almost out of the US. However, in 1972, DDT was banned after this book silent spring By Rachel Carson It made people aware of DDT’s devastating effect on wildlife, and eagles could turn back. In 2007, bald eagles were removed from the federal Endangered Species Act, and a decade later they were removed from Washington State’s protected species list—a major success story for conservationists and eagles alike.

Now, the birds face a new threat.

Bald eagles Seasonal migration In search of food – especially salmon, which is their favorite. While some eagles do not migrate at all if food remains available during the cold winter months, others migrate to areas with open water when lakes and streams freeze in winter. Northwest Washington, with its open rivers and open seas teeming with salmon, has historically had such a situation. It has been a shelter For these migratory eagles in winter. Adult salmon reach the end of their life after returning to reproduce during their spawning run. After the annual fall spawning run of salmon, thousands of carcasses litter the shores of Washington’s rivers.

However, the decline in salmon availability over the past century now threatens these eagles and other species that have long relied on the fish. Climate change has led to high river flows and severe flooding in late fall in Washington, which washes dead trout out to sea before they are eaten by eagles. In addition, many salmon populations in the region have declined due to other human-induced changes to their habitat, including dams and warming streams. Stream temperatures have increased in recent years as glaciers retreat and provide less cool water, atmospheric temperatures rise, and extreme heat waves become more common. These changes are bad news for cold-water species like salmon, which can experience heat stress and die when water temperatures get too high, and for the predators that rely on them, including bald eagles.

The Shoals Glacier on Mount Baker, which feeds the Nooksack River and provides cool water for salmon in the summer, has been retreating rapidly over the past few decades. Photo: Jenna Travers

To understand how feeding, migration, and habitat patterns of bald eagles in the Pacific Northwest may change in response to climate change, Ethan Duvall, Ph.D. student in the Department of Ecology and Evolution at Cornell University, spent two years studying eagles in a river basin in northwest Washington state and comparing his data to previous papers and research. His findingswill be released soon Northwest Sciencessuggests that due to the effects of climate change on salmon populations, “a large portion of the aggregating eagles are redistributing. [from rivers] to agricultural areas” in search of other food sources.

Duvall decided to begin this study at the end of his undergraduate studies at Western Washington University. In an interview with GlacierHub, he cited his interest in ecology and ornithology and the desire to conduct independent and relevant research as his motivation for undertaking this lengthy project. He surveyed a 30-kilometer stretch of the Knox River every week during the winter months and compared his data with previous surveys in the same area. It dates back to the 1970s. This extensive data set allowed him to understand not only current patterns of bald eagle migration and feeding, but also long-term changes due to human pressures.

In an interview with Duvall, he explained that bald eagles in the Pacific Northwest “respond directly to the availability of salmon carcasses.” As the salmon population declines, the eagles have begun to look for food in other areas, especially agricultural areas. According to the study, eagles are mostly concentrated near dairy farms and duck farms, eating cow udders and duck carcasses.

Eagles swarm the farm in response to farmers feeding them dead chickens. Photo: Dennis Jarvis/Flickr

The study also showed a significant difference in eagle abundance between two different watersheds in northwestern Washington, highlighting how differences in riparian management can drastically alter ecosystems. Since the 1970s, eagle abundance in the Nooksack River has increased dramatically, along with relatively healthy salmon runs. However, on the neighboring Skagit River, this one Different story. “Eagle abundance has dropped dramatically, at the same time as salmon populations have declined dramatically, largely due to damming,” says Duvall. Eagles in the area have been forced to move to the Nook Sac River or agricultural areas near Skagit to find food.

In terms of eagle conservation, Duvall emphasizes that “it is imperative that we protect our salmon populations and work to reduce human disturbance in our rivers.” He notes that if conservation managers and conservationists don’t act to address the issue of salmon declines in the Skagit, both chum and eagle populations may not survive. As climate change worsens, salmon runs will become increasingly threatened Local extinction– A phenomenon in which a population no longer survives in a place where it used to live, even if it survives elsewhere. This in turn threatens eagles and the people who rely on salmon for subsistence, cultural and economic reasons.

This study highlights the importance of addressing the ways humans affect rivers and species that rely on clean, flowing water in the Northwest. Without human action, bald eagles can no longer rely on this region of the United States for food during the winter months.

In the past, our community saved bald eagles and other species by taking on the challenging task of weaning our economy off toxic pesticides. It remains to be seen if we will take on the larger task of changing our energy systems to wean them off fossil fuels, reduce warming, and protect salmon, eagles, and other species threatened by climate change.


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