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Disaster. Collapse. Catastrophic failure.

These one conservation group is using to describe what happened on the Columbia River earlier this month, when around 16,000 adult Double-crested Cormorants—the entire nesting colony on East Sand Island—collectively abandoned their nests. The nests, which can hold up to seven eggs each, were then raided by ravens, gulls, and other predators, leading to the loss of thousands of potential chicks.

This type of mass abandonment isn’t typical for a cormorant colony; but then again, life hasn’t been too typical for the birds on East Sand Island. Their annual nesting spots on the mouth of the Columbia River, near the border of Oregon and Washington, have become the site of a . Between last May and October, the U.S. Army Corps of Engineers, with a permit issued by the U.S. Fish and Wildlife Service (USFWS), on the island. The Army Corps’s rationale is that during nesting season, the cormorants cut too deep into populations of juvenile salmon and steelhead trout, both of which are endangered. It hasn’t the cull may have on actual fish numbers—only stating that “potential maximum benefits could occur.”

The agency has also been oiling eggs from the colony—a process that kills the embryos—as part of a federal plan to slash the cormorant population on East Sand Island (which stands as the of Double-crested Cormorants in North America) from 13,000 breeding pairs to 5,600 pairs. The plan seeks to reduce cormorant numbers by nearly 60 percent by 2018.

But this guns-blazing approach is what led to the colony’s desertion, says Bob Sallinger, the conservation director for the ̽����ѡ Society of Portland. To Sallinger the plan has always seemed unsustainable, given that there’s an extraordinary amount of pressure being placed on the birds. “With harassment at this scale you absolutely set the stage for nest-colony collapse. No one should be surprised at this point that nests have been abandoned,” he says.  

The Army Corps, on the other hand, isn’t so sure. Army Corps spokesperson Amy Echols said that the agency isn’t using the terms “failure” or “collapse” to describe the abandonment event: They’re still waiting to see if the birds will return and recolonize the nesting spot. She also noted that the agency is investigating the incident and that it’s too soon to say what caused the birds to leave their nests.

According to Echols, this is what the Army Corps knows so far: The last time it oiled the cormorants’ eggs was Wednesday, May 11. The next day, Army Corps monitors confirmed that the birds had returned to their nests. When the human monitors returned to the nesting place the following Monday, however, all of the birds had left and the eggs had been ravaged. There was evidence of avian predators, including Bald Eagles, in the immediate area.

“This big of a disturbance is not something we have seen before out there, so it’s something new for us to explore,” Echols says.

Daniel Roby, a professor in the Department of Fisheries and Wildlife at Oregon State University who monitored the cormorants on East Sand Island for almost 20 years, says he hadn’t previously observed this behavior in the colony. Cormorants are sensitive creatures, he notes, and are extremely reactive to human disturbances on breeding colonies. It’s possible that the cumulative stress of the culling program, paired with another disturbance, such as a human or animal predator entering the island, could have caused the birds to abandon their nests.

Colony-wide desertion has previously been observed in smaller groups of culled cormorants. In 2010 a colony of about 9,600 birds in northern Lake Michigan—but they did so over the course of a breeding season, rather than in one fell swoop. Similar events with Double-crested Cormorants and other species, such as White Pelicans. “Complete nesting failure at waterbird and seabird breeding colonies is not especially rare,” Roby says. “What is so unusual about East Sand Island was how abruptly the abandonment occurred and how large the colony was when it suddenly abandoned.”

The Army Corps has suspended the cull as it waits to see whether the birds will return to their nests (the permit states there needs to be a certain number of cormorants present on the island). But the ̽����ѡ Society of Portland is calling for an independent investigation and complete termination of the plan. The cull, Sallinger says, was never the most effective way to improve salmon and steelhead populations. Plus, it has the potential to harm cormorants on a broader scale. When the Army Corps released its final documents for the cull, Michael Sutton, former vice president of the Pacific Flyway at the ̽����ѡ, countered that it would skim 25 percent off the entire Double-crested populace out West. The fallout, he said, would be felt across the region.

Last year, the ̽����ѡ Society of Portland, along with four other environmental groups and funding from the ̽����ѡ, against the Army Corps to stop the cull from moving forward. The case is still in progress—but more recently, courts have been ruling in favor of the birds. Just a week ago, a federal judge in D.C. that allowed tribes and wildlife agencies to kill cormorants in 24 states east of the Mississippi. The judge reasoned that the order violated the National Environmental Policy Act, stating that USFWS had overlooked the cormorants’ positive role in the ecosystem while overestimating the birds’ impact on the fishing industry.

There’s still a chance that the East Sand Island cormorants will come back this year, both Roby and Echols say. Last week, the Army Corps saw some increases in flock size on nearby islands, and about 4,000 cormorants have been spotted on East Sand Island—though not in the actual nesting area. If the birds re-colonize the area quickly enough, they could breed and rear their young in time for fall migration, Roby says.

If that happens, the culling may start back up, but Echols says it’s too early to know for sure. If the evidence shows that the Army Corps’s actions contributed to the abandonment, the agency would use that information to work with the USFWS to “determine a path forward.”

For Sallinger and Roby, that path needs to focus on the consequences of the cull itself. “Colony abandonment for one season would have far less of an impact on the population than the cull,” Roby says. If the missing birds return, they might face the same threats that caused them to escape in the first place. It’s just the latest in a long string of dead ends for the cormorants of East Sand Island.