The Whanganui District Council is worried about the welfare of four young white swans which have gone missing from a lake.
The cygnets were last seen at Virginia Lake on 23 December.
A member of the public has said they were gone three days later.
Council member Randhir Dahya says it's possible the birds were stolen, and the thief may try to sell them.
Mr Dahya fears the swans may starve to death because cygnets learn to feed from their parents.
He's asking the public to be alert to suspicious activity in the area, in case an attempt is made to take the three remaining young swans.
Mr Dahya says individuals can be prosecuted for the theft of wildlife from public parks.