Double-crested cormorants nesting on the Astoria Bridge could come with a high cost to the state and more frequent maintenance interruptions for motorists.
The birds, seasonal visitors to the North Coast, have just begun to return to the estuary for breeding and nesting. No one knows how many will decide to settle on the bridge this year, but it was clearly a popular spot last year, as birds from the region’s largest colony continued to be hazed off East Sand Island downriver.
The number of double-crested cormorants nesting on the bridge jumped from a dozen pairs in 2004 to around 1,700 pairs last year, according to monitoring reports cited by the Oregon Department of Transportation.
The leaps coincide with the beginning of lethal management of a massive double-crested cormorant colony on East Sand Island. The birds abandoned the island several times after the U.S. Army Corps of Engineers began shooting thousands of adult birds and destroying nests and eggs in 2015 to protect runs of young salmon.
The Audubon Society of Portland called a mass exodus in 2017 a “catastrophic collapse.”
Fish and wildlife researchers have since questioned the value of cormorant management in saving salmon. They say it was clear after each dispersal that cormorants were resettling on the bridge and farther upriver — areas where they could potentially impact even more salmon.
Cormorant droppings have accumulated on the bridge in layers so thick they have made it difficult for state inspectors to evaluate the structure. The droppings are also very corrosive, reducing the life span of the bridge’s protective steel coating.
“The potential expense we’re facing is a real worry to us,” said Department of Transportation spokesman Lou Torres.
The state repaints the Astoria Bridge every 20 years, a lengthy but necessary maintenance that has shut down lanes during busy summer months.
Work on the span only just concluded in 2018 and more work is planned in 2021 on the under truss, where many of the cormorants appear to nest.
“We’re really trying to get prepared for that,” Torres said.
He estimates it could cost around $80,000 to pressure-wash the bridge to complete required inspections. But that cost could quickly increase to $6 million if environmental agencies require the state to set up containment structures during pressure washing so bird waste does not simply get pushed into the Columbia River.
If cormorants continue to nest on the bridge in such high numbers, the state may also have to paint the bridge more often, every 15 years as opposed to every 20.
Under that scenario, Torres said, “We’re not going to have a lot of years where we’re not painting.”
Either way, the Department of Transportation is weighing its options as 2021 approaches. The department anticipates it will need to begin a hazing program to dissuade cormorants from nesting on the bridge. How to remove them is still an open question.
Several years ago, the state hired a company that set up noise cannons on the Interstate 5 Columbia River Bridge in Portland to disturb thousands of starlings that had colonized the bridge and whose accumulated droppings on the bridge, catwalks and roadways posed health and safety hazards.
The Army Corps does not link the movement of double-crested cormorants farther upriver to management actions on East Sand Island. The agency blamed attacks by eagles for the birds’ departures in 2016 and 2017.
Army Corps spokesman Jeff Henon suggested the birds may not have nested in large numbers on the bridge before because of the billowing containment structures that were around in 2014 during painting and maintenance. When the state moved on to other portions of the bridge and the containment structures were no longer necessary, the birds moved in.
But Torres noted that the bulk of that work was not in areas where birds usually nested and, besides, the number of nesting birds on the bridge during the spring and summer climbed steadily between 2012 and 2018.
“The numbers tell the story there,” he said.
The Army Corps did not shoot any adult birds last year, but did destroy eggs. This year, the agency plans to modify the island’s terrain, creating intertidal wetlands and further reducing nesting habitat to keep double-crested cormorants at the lower levels identified in a federal management plan.
But it’s not as though the cormorants’ relocation onto the Astoria Bridge and deeper into the estuary should have been a surprise.
Studies funded by the Army Corps before management of the cormorants even began indicated it was likely some of the birds would move into the estuary if they were hazed off East Sand Island.
Feasting on salmon
Though further investigation is needed, available evidence suggests the cormorants that have been nesting upriver only recently immigrated from somewhere else — their most likely origin being East Sand Island, said James Lawonn, avian predation biologist with the Oregon Department of Fish and Wildlife.
Past research on Caspian terns, also seasonal inhabitants of East Sand Island managed by the Army Corps, indicates birds that nest farther up in the estuary eat even more salmon than those nesting near the river’s mouth, where more types of food are available. It’s possible cormorants that nest upriver could eat three times more young salmon.
Now the state and other partners are looking into the impact of new cormorant colonies in the estuary on the survival of young salmon.
To Lawonn, how many cormorants are using the Astoria Bridge is a major piece of the puzzle.
One evening at the end of March, Lawonn set up a scope near the Port of Astoria’s West Mooring Basin near the bridge.
He wasn’t sure how many cormorants he would even see. It was still early in the season.
Double-crested cormorants appear inclined to return to nesting grounds where they have experienced success, but they also aren’t afraid to quest elsewhere for better options if they are running into trouble.
He wondered if birds that found safe and suitable nesting on the bridge would choose it first over East Sand Island, bypassing habitat where they had been hazed and shot at by humans and harried by eagles for the past several years.
The Army Corps will not begin monitoring East Sand Island for double-crested cormorants and nesting activity until the end of April or beginning of May.
Even as Lawonn trained his scope down the bridge’s length, the dark, snaking forms of cormorants on support structures at the base of the bridge caught the sinking sunlight and gleamed.
Lawonn counted over 650 double-crested cormorants that evening. A few days later, he counted 943.