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.