The reward has been increased to $25,000 for information leading to an arrest and conviction in the case of 13 bald eagles found dead Saturday on a Caroline County farm.
The reward was raised Wednesday with a pledge of $15,000 from the Center for Biological Diversity, an Arizona-based nonprofit.
"If they were poisoned or shot, the heartbreaking deaths of these 13 bald eagles is a crime. Those responsible need to be caught and prosecuted," Catherine Kilduff, an attorney for the nonprofit, said in a statement.
Federal wildlife authorities have not determined how the eagles died and say it is unclear if a crime was committed.
The eagles have been sent for autopsies at the U.S. Fish and Wildlife Service Forensics Laboratory in Ashland, Ore., said Catherine Hibbard, a spokeswoman for the service.
Previously, federal wildlife authorities and a group of nonprofits had offered $10,000 for information in the case.
No longer considered endangered, bald eagles are still protected by federal law.
On Saturday afternoon, police were called to the farm near the 3,800-acre Idylwild Natural Area after a man searching for shed deer antlers discovered four dead eagles. Officers with the Maryland Natural Resources Police searched the area and found nine more carcasses.
The birds showed no signs of trauma, police spokeswoman Candy Thomson said. But investigators believe the eagles all died within a short span of time. One possibility is that the birds died after eating poisoned rodents, Thomson has said.
Investigators have been going door to door searching for leads.