Belfast City Council is urged to improve security in Victoria Park, where a swan was decapitated on Wednesday night.
Ms Sheila Moffat of the Victoria Nature and Conservation group in east Belfast, said: "It is terrible that such a thing has happened. We have been urging the council to improve security for quite a while. Hopefully now they will close off the area where the birds are to protect them from the public."
The RUC, however, said there was no evidence that vandals killed the swan. They suggested an animal could have been responsible.