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Birds on the bridge: State, region consider managing cormorants

Double-crested cormorants have been nesting on the Astoria Bridge in greater numbers in recent years, causing headaches for the state as it looks to repair, repaint and maintain the important structure. Photo by Hailey Hoffman/Courtesy of The Astorian

ASTORIA, Ore. — One afternoon in July, motorists traveling on the Astoria Bridge from Washington to Oregon could have counted 13 dead cormorants on the roadside before they were halfway across.

For several years now, the number of dead birds has acted as an informal indicator of the growing colony nesting on supporting structures below.

And for the past two years, contractors with the Oregon Department of Transportation have frightened thousands of double-crested cormorants off portions of the bridge so crews could make repairs and repaint.

That $17.5 million maintenance project wrapped well ahead of schedule. But the birds remain. Harassed from one area of the bridge, they simply moved to another. 

It was an experiment of sorts, said James Lawonn, a wildlife biologist with the Oregon Department of Fish and Wildlife, and the birds responded more or less as expected.

For Lawonn, this made it clear that the bridge is the cormorants’ preferred breeding ground right now. If you want to get them off the bridge and keep them off, you have to consider the whole structure.

“But,” he added, “you also need to let cormorants know where you want them to go.”

When the next phase of maintenance begins on the Astoria Bridge in 2025, the Oregon Department of Transportation expects the presence of thousands of double-crested cormorants could again be an issue. But larger plans are also in the works. 

A draft recommendation from the Columbia Basin Collaborative proposes a new program to manage double-crested cormorants in the estuary. The collaboration — a partnership that involves Washington, Oregon, Idaho, Montana, tribes, federal agencies and other stakeholders – is tasked with developing recommendations to conserve and enhance salmon and steelhead in the Columbia basin.

According to a draft presented to the collaborative earlier this year, double-crested cormorants would be discouraged — through non-lethal approaches – from using the Astoria Bridge and encouraged to once again nest at a former colony on East Sand Island near the river’s mouth.

The cormorants abandoned the small island near Chinook, Wash., following several rounds of lethal hazing and habitat modifications by the U.S. Army Corps of Engineers between 2015 and 2018. The Corps argued that the birds were eating too many federally listed juvenile salmon and steelhead and their numbers needed to be reduced. 

Conservationists and researchers, however, warned that shooting the birds and destroying nests and eggs could cause cormorants to abandon East Sand Island and become an issue farther upriver.

In recent years, the Oregon Department of Fish and Wildlife has recorded a growing number of cormorants on the bridge. Throughout 2020 and 2021, the bridge was home to most of the breeding double-crested cormorants in the estuary. The birds’ corrosive guano and general presence has made regular maintenance and inspection work on the bridge difficult. 

In another twist, recent data shows the cormorants may be consuming more threatened and endangered salmonids at the bridge than they would at East Sand Island. 

“So that’s a big concern for recovery of those fish,” Lawonn said. He helped prepare the draft management recommendation for the Columbia Basin Collaborative.

“Cormorants act a lot differently the farther downriver they’re nesting, at least in terms of what their predation rates are on salmon,” he said.

At the mouth of the river, at East Sand Island, there are other types of forage fish to eat and the cormorants aren’t picky.   

But Lawonn said encouraging the birds back to East Sand Island is not an attempt to return to how things were before.

The original East Sand Island colony contained about 13,000 breeding pairs, representing around 40% of the double-crested cormorant population west of the Rocky Mountains. There are currently only around 4,000 to 5,000 breeding pairs across the entire Columbia River estuary. 

“So we’re talking about a much smaller number of birds that would be attracted back to East Sand Island,” Lawonn said.

The goal would remain the same: to reduce predation on listed salmon and steelhead. 

But a large-scale management plan for cormorants in the estuary faces challenges.

It would require participation by many different entities including the Bonneville Power Administration, Columbia River basin tribes and the Columbia River Inter-Tribal Fish Commission, the federal National Marine Fisheries Service, the Corps, the U.S. Coast Guard, the U.S. Fish and Wildlife Service and the state transportation departments and fish and wildlife departments of Oregon and Washington.

There are also a number of uncertainties, according to the draft recommendation.

First, it isn’t clear exactly how much the cormorants’ consumption of salmon and steelhead  impacts the long term abundance of these fish in the Columbia River. 

Second, the cormorants devour hundreds and even thousands of tons of forage fish in the river annually — the majority of which are not salmon and steelhead. It isn’t clear what happens when the number of cormorants active in this food web is reduced. 

Then there is the cost: an estimated several million dollars annually for the first few years. Just how expensive depends on how the cormorants respond to efforts to move them off the bridge and to East Sand Island and what challenges they face in once again nesting at the island.

So far, no one has been designated to perform or fund the management work.

Another curious — though not well understood – challenge could be the shifting behaviors of the cormorants themselves.

Researchers have started seeing that cormorants increasingly seem to prefer nesting on human-made structures. 

In a 2018 study of where double-crested cormorants were nesting in California’s San Francisco Bay Area, researchers recorded more birds nesting on bridges spanning the bay. The bridges were also where they saw the first large colonies start to rapidly form in the 1980s through peak years in the early 2000s. 

“The proximity of the bridges to historical roosting sites, and the type of protected truss-work under the bridges, have afforded cormorants a shaded, predator-free place to nest, allowing the recovering (double-crested cormorant) population to expand throughout the estuary,” they wrote.

North, in the Salish Sea, researchers saw a shift from the usual cliffs and small islands to bridges, transmission towers and other human-made structures. 

Lawonn says they are seeing something similar along the entire Oregon Coast — though the Astoria Bridge remains a standout in terms of the number of nesting pairs. It is possible that rebounding bald eagle populations play a role.

“Bald eagle abundance continues to increase at many areas across the Oregon Coast and bald eagles can limit cormorant use of traditional habitats like islands or stands of large trees,” Lawonn said. “And in fact, we’ve seen that. We’ve seen eagles driving cormorants from those colonies.”

For now, cormorants on the Astoria Bridge — from spring through fall — are a fact of life for ODOT.

The pyrotechnics the state used to keep birds away from work areas over the past two years were successful, said spokesman David House. This hazing cost an estimated $225,000 and could become part of the business of the bridge, though expenses might be lower in the future.

“It’s not a huge cost,” House said. “But there is a cost.”