U.S. Fish and Wildlife Service officials are trying to pinpoint the cause of death of nine eagles and a red-tail hawk in Whatcom County that they think were poisoned.

“What concerns me is we really don’t know how many eagles are affected,” said Mary Jane Lavin of the wildlife service said. “We know what we found.”

Medical evidence indicates the birds died quickly from a powerful pesticide, probably after eating poisoned starlings, Lavin said.

Bird experts don’t know the source of the poison, but suspect it’s a pesticide mixed with corn to kill starlings, said Sharon Wolters, director of Sardis Wildlife Center.

“The way these eagles are dying, it’s horrible,” Wolters said.

Farmers sometimes poison starlings, a common barnyard pest. The poison remains in the starlings, and any scavengers that eat the birds can die.

Lavin fears more birds may have died, but haven’t been discovered yet.

A total of 10 eagles have been found in the Lynden, Sumas and Ferndale areas, all with the same symptoms, Lavin said.