In Spring of 2021, songbirds began dying off in the Washington, D.C., Maryland and Virginia areas and the reports began spreading north, leading the Pennsylvania Game Commission to issue an alert on July 1 2021 asking state residents to take down bird feeders and birdbaths to prevent birds from congregating.

It was thought the birds could be spreading the illness that caused crusty eyes, neurological symptoms and eventually death as they fed and bathed. The species most affected were blue jays, American robins, grackles and European starlings. In the end, the Wildlife Futures Program confirmed cases of the mysterious avian illness in 12 Pennsylvania counties through testing and identified 22 other counties that had probable cases.

Then, almost as quickly as they started, the songbird deaths subsided. By mid-August, the Game Commission dropped its recommendation against feeding birds.

What killed the birds in spring and summer 2021?  That has yet to be answered.

According to Martin J. Hackett, communications director for the School of Veterinary Medicine at the University of Pennsylvania, results have been inconclusive. “We went through a series of diagnostic tests and it was inconclusive. The testing failed to reveal a clear cause for this mortality event,” Hackett said. “So we are not quite sure what happened.”

The Game Commission said previously that several pathogens had been ruled out, including salmonella, chlamydia, avian influenza virus, West Nile virus, Newcastle disease virus, herpesviruses, poxviruses and trichomoniasis parasites.

One positive outcome is that researchers may be better positioned to use a process called metagenomics, which Hackett called a promising new tool for pathogen detection if faced with a similar event in the future. “That could be applicable to not only, for example, the songbird mortality event but other issues of wildlife,” he said.

It also raised public awareness of the importance of keeping bird feeders and water sources clean. The Game Commission recommends cleaning and disinfecting feeders and bird baths at least weekly to prevent the spread of infectious diseases between birds.