Southland farmers are being asked to keep an ear open for the distinct caw of a rook.
The regional council has received reports the pest bird has been spotted in Te Anau.
Biosecurity officer Tim Riding says the region's rook population is low due to quick reports by farmers and prompt action by the council, and he wants to keep it that way.
He says rooks are cunning and aggressive pests that can destroy crops in a couple of days. They make large, messy-looking nests of up to a metre in diameter, often in macrocarpa trees.
Mr Riding says farmers should report any sightings of the bird and in particular its nest sites.
He says the council takes care of all the costs of controlling the birds.