Four bald eagles have died in Delaware after being found about 30 miles from where 13 eagles were found dead last month in Maryland.

One of the eagles was found dead Saturday near Dagsboro, Del., wildlife officials said. Three more died after attempts at resuscitation failed, the state’s Natural Resources police said.

Those three eagles were part of a group that was found disoriented in a farm field in Sussex County, Del., about a mile from where the first dead eagle was discovered, Delaware authorities said. Two more eagles from the group were being cared for at a bird rescue organization in Delaware.

Three other eagles in the same group flew away before they could be captured and undergo health evaluation. Authorities said they did not know just how many eagles were affected.

The causes of the deaths were not known. Delaware Natural Resources police said they were actively investigating but declined comment on possible causes.

Authorities have said poison may have caused the deaths of the eagles found last month near a farm in the Federalsburg, Md., area.

The U.S. Fish and Wildlife Service has been investigating and has said the Maryland deaths did not result from natural causes. However, no specific cause has been determined. A reward has been offered for information. Delaware officials said they expected the federal agency to look into the weekend deaths as well.

Dagsboro, Del, is about 30 flight miles southeast of Federalsburg, which is on Maryland’s Eastern Shore and about five miles from the Maryland and Delaware border.