Groups of songbirds have been turning up dead throughout the Delaware Valley recently but their cause of death remains a mystery to scientists and wildlife officials, writes Frank Kummer for The Philadelphia Inquirer.

Similar deaths have been reported in other parts of Pennsylvania and across several more states, going back to April.

The rash of songbird deaths has been deemed unusual by officials and wildlife experts. They are appealing to the public to stop feeding birds from feeders and providing water in birdbaths until scientists can find the cause of the illness. The current belief is that grouping birds together can contribute to the spread of the disease.

Various species are affected by the unknown malady. They have all been found with ocular and neurological issues.

According to Lisa Murphy, a veterinarian and director of Pennsylvania Diagnostic Laboratory System at New Bolton Center in Kennett Square, scientists consider the illness to be “worrisome.”

“Not one disease or disease agent jumps,” she said. “This does seem to be something unique and unusual.”

To try and untangle the mystery, Pennsylvania officials are now asking people to report unusual occurrences of bird deaths online to the Wildlife Futures Program.

Read more about the songbirds in The Philadelphia Inquirer.