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INDIANAPOLIS — Hoosiers in nine Indiana counties should continue to keep their birdfeeders stored safely away.

The Indiana Department of Natural Resources recommends that people in nine counties—Allen, Hamilton, Hendricks, Johnson, Lake, Marion, Monroe, Porter and St. Joseph—refrain from feeding birds as the agency continues to investigate cases of sick and dying songbirds.

The new guidance this week means that people in Indiana’s other 83 counties can use their birdfeeders. DNR has the following recommendations:

Seed and suet feeders should be cleaned at least once every two weeks by scrubbing feeders with soap and water, followed by a short soak in a 10% bleach solution to keep birds healthy and limit the spread of disease. Hummingbird feeders should be cleaned at least once a week with a 10% bleach solution and rinsed thoroughly.

In late May, the agency started receiving reports of sick and dying songbirds from Monroe County with neurological symptoms, eye swelling and crusty discharges around the eyes. DNR later asked Hoosiers to remove their birdfeeders and birdbaths entirely while they investigated the issue.

Biologists with the agency have confirmed more than 500 possible cases in 72 Indiana counties. Several causes have been ruled out, and the cause of the illness remains unknown.

The problem affects the following species: American robin, blue jay, brown-headed cowbird, common grackle, European starling, various species of sparrows and finches, and northern cardinal.

“All birds have tested negative for avian influenza, West Nile virus, and other flaviviruses, Salmonella and Chlamydia (bacterial pathogens), Newcastle disease virus and other paramyxoviruses, herpesviruses and poxviruses, and Trichomonas parasites. Other diagnostic tests are ongoing,” DNR said in update this week.

DNR believes the illness is consistently affecting specific areas, which is why it’s lifting its moratorium on bird feeding in most Indiana counties. The agency doesn’t believe there’s an “imminent threat” to specific bird species or the state’s overall bird population.