INDIANAPOLIS, Ind. (WOWO):  The Indiana DNR is still searching for a reason behind the death of numerous songbirds across the state.

The sick and dying songbirds have shown neurological signs of illness, such as tremors, stumbling, weakness and lethargy along with also displaying crusty discharge around the eyes.

According to the IndyStar, officials with the Indiana DNR still are not yet sure what the cause of the illness is, but the birds have tested negative for West Nile virus and avian influenza, as well as for other conditions such as: flaviviruses, salmonella, chlamydia, Newcastle disease virus, herpesviruses, poxviruses and Trichomanas parasites.

More than 400 birds have been reported showing signs of illness, and Hoosier residents are being asked to keep bird baths and bird feeders inside.