A reward for information is being offered after two seagulls were injured in a crossbow attack.
Both gulls, who are believed to still be alive, have been spotted in Scarborough, North Yorkshire, with bolts pierced through their heads.
The People for the Ethical Treatment of Animals (Peta) has put up a £1,000 reward for information leading to the conviction of those responsible.
RSPCA staff are trying to find the birds so they can treat them.
The RSPCA's Inspector Geoff Edmond described the incidents as "appalling", while Peta spokeswoman Suzanne Barnard said they were "vicious".
The attacks have also been condemned by the Royal Society for the Protection of Birds (RSPB).