(Clockwise from upper left) Bluejays, brown-headed cowbirds, American robins and cardinals are among the common backyard songbirds struck with the mystery disease.

A mysterious disease began killing songbirds last spring, and despite scientists’ best efforts, they cannot identify the problem, which has abated in some states. 

In April, scores of birds in the greater Washington, D.C. area began displaying strange symptoms. Their eyes were swollen and crusty; some became disoriented, started twitching and died. By June, similar reports were rolling in from Maryland, Virginia, West Virginia, Delaware, New Jersey, Ohio, Tennessee, Florida, Indiana and Pennsylvania, according to the U.S. Geological Survey Wildlife Health Information Sharing Partnership.

Lab tests have ruled out causes from West Nile virus and avian flu to ingesting cicadas. Scientists are trying to determine if this is a completely new pathogen or multiple factors working in tandem.

“The fact that this is a new problem is cause for concern. We don’t know what’s going on. It’s affecting young birds, future generations,” said John Herbert, Non-game Bird Biologist with the Rhode Island Dept. of Environmental Management.

Thus far, the only deterrent has been the removal of bird feeders, since birds that congregate at feeders and baths can transmit disease to one another.

Although there have been no reports of sick and dying birds in Connecticut, state officials and local wildlife specialists recommend removing bird feeders and cleaning them, and birdbaths, with a 10 percent bleach solution to kill lingering pathogens.

Smithsonian’s genetics lab and others are still working to definitively rule out a cicada link, but Brood X cicadas died in mid- to late- June, and birds are still falling sick. As recently as July 8, a male American robin was brought to Tamarack Wildlife Center in Saegertown, Pa. with head twitches and closed, crusted eyes. He was able to stand, briefly, before he died.

In the meantime, young, healthy blue jays and starlings—the species among the hardest hit by the illness—are beginning to show up around Washington, D.C. Wildlife experts say that the removal of backyard bird feeders is likely helping to reduce the number of affected birds.