INDIANAPOLIS — Sick and dying songbirds stricken with an unexplained illness have now been found in three-quarters of Indiana’s counties, state wildlife officials say.

The Indiana Department of Natural Resources said the sick and dying songbirds have been discovered in 69 of Indiana’s 92 counties, up from 53 counties two weeks ago, The Indianapolis Star reported.

The sick songbirds were initially found in late May in southern Indiana’s Monroe County.

The DNR continues to investigate the issue and the possible causes behind the sick birds. The state agency has asked people to take down bird feeders as they try to determine the cause or causes.

Sick songbirds have also been found in Ohio, Kentucky, Virginia, Maryland and Pennsylvania.

The birds show symptoms of neurological illness, such as eye swelling and crusty discharge around the eyes. Some have also been lethargic and weak, stumbled or had tremors.

Songbirds such as American robins, blue jays, grackles, starlings, and sparrows appear to be those that are primarily affected. But brown-headed cowbirds, European starlings, house finches, northern cardinals, red-headed woodpeckers and wrens have also been found sick.

The DNR is just over three weeks into their investigation, and has sent several samples to the Indiana Animal Disease Diagnostic Laboratory for testing.

Indiana residents can report any cases of sick birds they found to the DNR online at on.IN.gov/sickwildlife. They are urged to use disposable gloves and dispose of the bird in a plastic bag if they need to touch the bird.