One of the bald eagles found dead in a farm field on Maryland’s Eastern Shore in February. A total of 13 were found. (Courtesy of the Maryland Natural Resources Police)

Federal wildlife officials said they are looking for suspects in the death of 13 bald eagles found on the Eastern Shore after a necropsy showed the birds did not die from natural causes or disease.

The update on the mysterious deaths of the birds came Thursday from a forensic lab of U.S. Fish and Wildlife Service in Oregon, which is working on the case. There is a $25,000 reward being offered for information that leads to an arrest and conviction.

The death of the eagles drew national attention and it is the largest single die-off of bald eagles in the state in 30 years.

The eagles were found Feb. 20 in Federalsburg, Md., by a man who said he was out looking for antlers that deer might have shed. He came across four dead eagles. When wildlife authorities arrived, they found nine more nearby. The eagles should no obvious signs of trauma, officials said.

The National Fish and Wildlife Forensics Laboratory in Ashland, Oregon, is trying to figure out what killed 13 bald eagles from Maryland's Eastern Shore. They have ruled out diseases and are now focused on “human causes.” (Courtesy of National Fish and Wildlife Forensic Laboratory)

In a statement released Thursday, the federal wildlife agency said necropsy results showed the 13 eagles “did not die of natural causes, including disease.”

“Our investigation is now focused on human causes and bringing to justice the person (s) responsible for the death of these eagles,” the statement said.

Experts on bald eagles said they still believe the birds’ death involved some sort of pesticide or poison that may have been used to get rid of predators of livestock or rodents. If the animals died outdoors and the eagles ate their carcasses, the birds also could have gotten sick.

Ed Clark, president and founder of the Wildlife Center of Virginia, said the latest finding from the federal wildlife officials is a “declaration of the obvious.”

“If there was any type of natural occurrence you would not find that number of dead bodies in one spot,” he said. “Which means whatever killed them, killed them quickly and they didn’t get very far.”

Clark said a case two years ago in Wisconsin was considered high profile and “hopefully sent a message” on using pesticides on prey. Farmers in Wisconsin used an illegal pesticide to try to get rid of coyotes and wolves.

More than 70 wild animals, including at least two bald eagles, vultures, coyotes, owls and a bobcat were killed and the landowners were ordered to pay over $100,000 in restitution and fines, according to Clark who testified in the case.

In the latest Maryland case, wildlife officials said it is an important move that they have ruled out disease, including avian influenza, because of the high concentration of migratory birds and the large number of poultry farms in that area.

Federal and state officials said they will not put out more details because they believe it could compromise the investigation. The Maryland Natural Resources Police is also helping on the case.

Anyone with information is asked to call 410-228-2476.