Cormorants are protected. But their poop is corroding a bridge across the Columbia River

Cormorants by the thousands have taken up residence under the landmark Astoria-Megler Bridge over the Columbia River.

Their poop can corrode the bridge and that is unacceptable to the Oregon and Washington transportation departments. But what actions to take against the protected birds and whose responsibility that is are up in the air.

The abundance of double-crested cormorants can be hard for the average onlooker or motorist to appreciate. The skittish diving birds look like closely-packed, slender black shadows as they roost and nest on beams and ledges well out over the river. But the rapid-fire whir of clicks coming from a tally counter in the hand of Oregon Department of Fish and Wildlife biologist James Lawonn underscored the multitude of arrivals.

About once per week, Lawonn plants a spotting scope on the end of a jetty in Astoria to survey the underside of the long, skinny, arching bridge over the Columbia River.

"The counts that we're getting are averaging around 8,500 this spring and we're not (even) getting any of the birds that are using the Washington side," Lawonn said on a recent Monday.

Lawonn said the cormorant numbers on the Astoria bridge this spring are around ten times higher than a few years ago. The surge of birds coincided with the shrinking of a man-made island seven miles downstream, where cormorants have been hazed and shot. East Sand Island was previously the biggest cormorant colony in the Lower Columbia estuary. The U.S. Army Corps of Engineers acted there to reduce predation on threatened salmon. But it may have simply redistributed the problem -- or even made it worse according to Oregon's Department of Fish and Wildlife.

"This is not according to plan," Lawonn said as he gazed across the river. "We don't want them on the bridge."

Lawonn described a two-fold problem. The cormorants on the Astoria bridge prey more heavily on young salmon migrating out to sea than do waterbirds closer to the ocean. Thirteen runs of threatened or endangered Columbia, Snake and Willamette River salmon pass beneath the hungry mouths perched on the bridge.

The other issue is encrustation and damage to the span itself from guano. Oregon Department of Transportation spokesperson Lou Torres said the status quo is unacceptable to his agency.

"There's some urgency in that we're required to inspect the bridge periodically, at least every couple of years," Torres said. "We have to be able to get our bridge inspectors to where they can see what's going on."

Torres said the highway agency is worried about the corrosive effects of the bird droppings. The acidic cormorant poop threatens to mess up a $75 million paint job that drivers across Washington and Oregon are paying for through gas taxes. The bird profusion may require the bridge to be cleaned more often too, which Torres figured could cost millions.

The Oregon Department of Transportation is in charge of maintenance of this cross-border bridge, but all costs are split 50-50 between ODOT and the Washington State Department of Transportation.

Army Corps of Engineers cormorant project manager Bob Winters said a range of federal, state and tribal agencies are meeting to brainstorm how to get the birds to move on.

"We're coming up with possible solutions," Winters said by phone from Portland. "One of them was trying to perform some kind of hazing activity, but we were informed by ODOT that they don't have any structures underneath there to get people down there to haze."

Double-crested cormorants are abundant throughout North America. They are not endangered, but they are federally protected under the Migratory Bird Treaty Act. State biologist Lawonn said everyone prefers non-lethal solutions.

"We've talked about everything from disco balls under the bridge -- that's only half in jest -- to eagle kites to high pressure water hoses," Lawonn said.

Lawonn said shooting the diving birds is not on the table, as happened in 2015-16 at the island colony near the river mouth.

ODOT wants the wildlife agencies to reach a decision on hazing before next spring.

"We can't just proceed and do anything we want because these birds are protected," Torres said. "We haven't made any concrete decisions yet about what we're going to do."

The Army Corps' Winters said his agency's jurisdiction when it comes to cormorant management is limited to the man-made islands of dredged sediment in the river.

Torres said the partner agencies have not yet hashed out who will pay for the extra costs of hazing or bridge modifications. The potential sums are unknown at this point.

The Astoria-Megler Bridge was originally completed in 1966. ODOT is about three-quarters of the way through a multi-year project to rehab and repaint the four-mile long bridge. The painting work was paused after last construction season and is scheduled to resume in 2022.

Winters said the resumption of bridge painting may scare off cormorants too. He noted that it is not entirely novel for cormorants to nest on the landmark span. The bridge has been the home to a few hundred breeding pairs for a long time. This year's peak cormorant tally of nearly 10,000 individuals was recorded earlier in the spring as outmigration of juvenile salmon began. The latest counts are lower.

"The population on the bridge is decreasing as the population at East Sand Island is increasing," Winters said in an interview Tuesday. "(Egg) incubation has started on East Sand Island, so that is a good sign."

Winters said the Corps is OK with a repopulation of East Sand Island as long as the birds settle within a predefined 1.3 acre zone and don't exceed a certain threshold of breeding pairs.

"We want them on East Sand Island," Winters said. "That would actually be beneficial."

Lawonn also described a shift of the cormorants back downstream to the low-lying island near the river mouth as the preferred outcome.

"It's complicated. It's ecology, right?" Lawonn sighed. "A lot of moving parts."

[Copyright 2019 Northwest News Network]