At the end of May, wildlife managers in the District of Columbia and multiple mid-Atlantic states started fielding reports about hundreds of sick and dying birds, afflicted with eye and nerve issues that couldn't be explained. Now, the mystery illness has spread to the South and Midwest, and scientists are trying to figure out what's causing it. Per a US Geological Survey release from earlier this month, birds cited in reports in DC, Maryland, Virginia, and West Virginia were found to have "eye swelling and crusty discharge," as well as "neurological signs," which NBC News notes include seizures and not being able to stay balanced. For the birds that have perished, "no definitive cause of death is identified at this time," the release notes. Meanwhile, birds in Kentucky, Ohio, and Indiana are showing up with similar issues. Wildlife officials in the latter state says tests for avian flu and West Nile came back negative, per the Guardian.
In addition to the possible spread of an infectious disease, which is scientists' first guess, Laura Kearns, a biologist with the Ohio Division of Wildlife, tells NBC the birds may also be falling ill from pesticides or even due to the recent cicada emergence. The Guardian notes that mass mortality events involving birds have also been tied in the past to inclement weather, including a mass die-off in New Mexico last year in which already starving migratory birds headed right into an unusual winter storm and ended up dying by the hundreds of thousands. The USGS notes that birds hanging around feeders and birdbaths can transmit disease, so the agency is recommending that the public stop feeding birds for the time being; scrub down feeders and birdbaths with a 10% bleach solution; avoid handling birds; and keep pets away from sick or dying ones, which should be reported to district or state wildlife conservation groups. (Read more birds stories.)