SPCA Wellington is hunting for those responsible for putting trinkets on sparrows which are leading to cruel deaths, many by starvation or thirst.
For years someone has been "decorating" birds in the eastern suburb of Kilbirnie but in the last few months, a significant spike in numbers has emerged.
SPCA regional manager for the central region Ros Alsford said someone has been decorating the birds with tinsel, bits of wire decoration and rings.
"We've seen some Christmas tinsel and ribbons, wire decorations with beads on them and very elaborate rings on some birds," she said.
"We've had so many calls, numerous people are incredibly concerned about it so we would like somebody to come forward if they've got any information.
"There's only three streets in Kilbirnie that this seems to be happening, so it definitely an intentional thing."
Alsford said most of the birds had been found in the Salek and Te Whiti St area but was unable to confirm the third street.
Natural movements and progression of the birds are restricted when they are decorated, often around their necks, wings, feet and beaks.
Members of the public have handed in birds throughout last year but the numbers started to increase over the Christmas period, Alsford said.
"Obviously, someone is doing it intentionally because it's not natural behaviour for birds to have like this," she said,
"We've seen incidents of this throughout last year ... birds who were brought that had already been deceased, some were still mobile but in a really bad condition.
"It seems to be only sparrows, it's most odd and unusual - it's something we're concerned and worried about."
The SPCA isn't sure if the person is being intentionally cruel, however, due to the distressing nature of the decorations they want the person to stop.
An appeal was posted on SPCA Wellington's Facebook page, seeking information from the public which would help solve "the case of cruelty".
"To date, we have been unable to identify who is responsible and the Wellington Inspectorate Team would like to speak to those involved," the post said.
"If you have any information, or would like to make an anonymous tip, please contact our call centre on (04) 389 8044. Your help will be greatly appreciated."