PORTLAND, Ore. -- A cormorant colony along the Columbia River has suffered a complete collapse after a "significant disturbance" last weekend.

More than 16,000 birds have abandoned the East Sand Island cormorant nesting colony, according to the U.S. Army Corps of Engineers.

"Independent monitors surveying the East Sand Island double-crested cormorant colony reported on Monday, May 16, that the colony had abandoned all nests," a release on the agency website reads. "This disturbance resulted in nest abandonment and the subsequent loss of cormorant eggs by avian predation (gulls, eagles, crows)."

A US Army Corps spokesperson said that 4000 of the cormorants returned to the island Wednesday but were staying away from the colony. Biologists are looking for the other 12,000 birds in the estuary area and beyond.

The corps has killed more than 4,500 birds over the past year in an effort to protect the salmon population there.

“The agencies have turned East Sand Island into a killing ground and put the birds under tremendous stress," said Bob Sallinger of the Audubon Society of Portland. "Nobody should be surprised that the colony failed under these conditions."

Sallinger said the colony was the largest Double-crested Cormorant colony in the world.

“This is simply wanton slaughter and it has now put the entire western population of cormorants at risk," he said. "To even consider restarting the killing this season or in the future after a complete colony collapse would be unconscionable.”

The incident is under investigation. Culling activities have been suspended. Sallinger said the Audubon Society of Portland is calling for a permanent end to the cormorant killing program.