An increase in the number of rooks in Waikato is worrying officials.
Waikato Regional Council is asking for help from landowners to spot rooks.(File image) Photo: 123rf
The bird was introduced to New Zealand in the 1860s to hunt insects but has become a pest by tearing up crops and ruining pastures.
Over the past few years, rooks have escaped pest control due to Covid-19 restrictions, and their dwindling population is bouncing back.
For Waikato Regional Council, the hunt is back on - but without help from landowners, it is like looking for a needle in a haystack.
Biosecurity pest animals team leader Brett Bailey said a task which required cooperation.
"It's a good time of the year to start seeing rooks as it's breeding season, which is when they congregate together," Bailey said.
"It's important that landowners don't try to get rid of them themselves, because we don't want to scare them and make them fly away and nest somewhere else."
Sightings could become more common in the upper North Island.
"We've had new sightings reported from north Waikato and South Auckland areas, which suggests rooks are heading north," Bailey said.
Rooks prefer to build their nests in eucalyptus trees and were previously known to build enormous colonies with hundreds of nests. But that was a thing of the past, Bailey said.
Before last year's breeding season, there were fewer than 40 rooks in Waikato, and their population has steadily dropped since the council started controlling them in 2002.
Waikato Regional Council is encouraging landowners to contact biosecurity officers if they become aware of a rook nest.