Witnesses saw birds "falling from the sky" and the Audubon Society has launched an investigation after at least 10 crows have been found dead in Northeast Portland since Tuesday.

The Portland Audubon Society, the Oregon Department of Fish and Wildlife and the U.S. Fish and Wildlife Service were all called in after the birds were discovered in the area of Martin Luther King Jr. Boulevard and Northeast Jessup Street, the Audubon Society said in a statement.

"While it cannot be confirmed until the birds have been tested, the deaths are consistent with some sort intentional or unintentional exposure to toxic substances," Bob Sallinger, conservation director for the Audubon Society, said.

Crows flock to urban settings in great numbers during the winter months, seeking warmth, food and safety in numbers. They often gather in groups that can number in the thousands, and the noise and mess that accompanies the flocks can be a nuisance.

A similar die-off of crows, in which at least 30 birds perished, was reported in downtown Portland in 2014.

While 10 birds have been found dead in this most recent spate of deaths, Salligner said he fears the problem could be more widespread.

"We're picking up the ones that are easily visible from the street," he said. "But we're only able to see a fraction of what's out there. Our concern is that this could be much bigger."

Sallinger said if the birds are indeed being poisoned, it could be dangerous for more than just crows.

"We advise the public to NOT handle dead or sick crows," he said in a statement. "If this is a poisoning event, there is potentially a risk to both pets and wildlife that might scavenge the crows as well as to humans that may handle the crows."

As a protected species under the Federal Migratory Bird Treaty Act, killing crows is illegal except under specific circumstances and the Audubon Society offered a $1,000 reward for information "that leads to identifying the cause of this crow mortality event."

Anyone with information was asked to call 503-292-0304.

-- Kale Williams

503-294-4048