Officials in Florida say someone has been attacking the state's pelicans, slashing the pouches of the oversized birds, which often die as a result.
Ten injured pelicans were found in the Florida Keys, sanctuary to a bounty of US wildlife, five of which died of their injuries, said officials.
Five pelicans that survived the attack were rescued by the Florida Fish and Wildlife Conservation Commission.
"Right now we don't have any leads," said FWC spokesman Robert Dube.
"We have no idea" who is behind this, he said, adding that authorities are offering a reward for information leading them to the perpetrators of the attacks.
"We are hoping that maybe the reward money will lead to a tip or some information on the suspect," Dube said.
Pelicans, which congregate in coastal areas of the state, eat vast quantities of fish, which they store in pouches on the underside of their enormous beaks.
Slitting their pouches makes it impossible for the birds to feed themselves, and they eventually starve to death, Duhe said.
"They can't hold any fish, if they grab a fish it would fall out," said Dube.
"They have a slow and agonizing death until they starve to death."