The Wellington SPCA says someone is killing sparrows by placing jewellery around their necks.
The SPCA said five dead birds had been found with wire rings around their necks in the area around Salek Street and Te Whiti Street in Kilbirnie.
Spokesperson Mark Collyns described the rings as decorative in nature.
But he said the rings were becoming trapped in the birds' beaks when they tried to remove them.
Mr Collyns said the birds would have died a slow death from starvation.
He said the SPCA was appealing for the person responsible to stop putting jewellery on the birds, and that they may have broken the law.
Senior animal welfare inspector Ben Lakomy said it was possible someone was trapping the adult birds and decorating them.
He added that, if the birds were dying as a direct result of the necklaces, it could be an offence against the Animal Welfare Act.