Two seagulls were killed and a further four were so severely injured they had to be put down after they were shot with an air rifle on Teesside.
RSPCA inspectors were called to Northgate in Hartlepool following complaints from members of the public.
The RSPCA described the case as shocking and appealed for information.
RSPCA inspector Sue Craig said: "This is just one of many irresponsible airgun-related incidents inspectors regularly have to deal with."
He added: "Many afflicted wild animals will hide away to die painful and lingering deaths, and air pellet entry wounds are difficult to detect by the untrained eye.
"If anyone saw, heard or knows anything about this incident we are keen to hear from them urgently."