The birds, dressed in tinsel, have been found in the Wellington suburb of Kilbirnie since 2015 - and there was a surge in reports during the last festive period.
The SPCA said it received 10 reports of sightings in November and a new report every day of a decorated bird this week.
The decorations stop the birds from flying, eating and drinking and lead to their death.
The SPCA hasn't been able to find the person responsible and is treating it as an ongoing investigation.
The reports are of a variety on non-native birds decorated in tinsel and other decorations, including gold and red tinsel bows, pink and blue ribbons and yellow feathers.
"We don't yet know if this is an act of intentional cruelty, but the birds are suffering so we're speaking out in the hopes that it stops," SPCA Wellington said.
"After extensive efforts by our Inspectorate Team we were unable to find the person responsible. We are continuing to treat this as an ongoing investigation."
Anyone with information or sightings of decorated birds is urged to contact the SPCA's Wellington centre on (04) 389 8044.
