Investigations have begun after 13 bald eagles were discovered dead in Maryland, according to Reuters. A spokesperson for the U.S. Fish and Wildlife Service stated that the birds' cause of death was unknown until a medical examination could take place and that it was not certain whether the birds had been killed deliberately.

The birds were discovered on Saturday afternoon by a man who was looking for deer antlers on the ground but discovered the bodies of four dead eagles, according to the Associated Press. Maryland Natural Resources Police spokesperson Candy Thomson stated that officers found an additional nine eagle bodies after searching the grounds themselves.

The incident marks the single largest mass death of bald eagles in Maryland in the past three decades, according to NBC News. While the cause of death of the birds is currently unknown, the bodies showed no signs of trauma, and it is believed that they all died within a similar time frame. Thomson has suggested that consumption of poisoned animal carcasses as one possible answer to the mystery.

"What happens is that when farms have rodent problems, landowners will put out poison to control it, and the eagles will eat the poisoned animals," Thomson told reporters.

Bald eagles stopped being classed as an endangered species in 2007 but remain protected under the Bald and Golden Eagle Act.

A $10,000 reward has been offered for any information regarding the birds' deaths that could lead to a conviction, coming out of the pocket of various federal wildlife authorities and nonprofit organizations, according to the Baltimore Sun. Authorities have urged anyone with relevant details to contact the U.S. Fish and Wildlife Service Office of Law Enforcement in Cambridge.