Coastal Otago biosecurity delivery lead Simon Stevenson said rooks were active in spring, eating newly sown crops and causing significant damage.
Rooks had been reduced to very low levels but there was the potential for the population to increase again, he said.
The public could help the council map the nests of the last remaining birds, he said.
ORC and Environment Southland had worked together to reduce the many thousands of breeding pairs in the South during the 1980s and 1990s.
Southland was "rook-free", but birds continue to be sighted in Otago.
As rooks were intelligent and wary birds it was important people report them to the council, rather than shoot at them.
An unsuccessful shooting attempt encouraged rooks to disperse and made them very wary and much more difficult to control.
By contacting the council, effective control options could be undertaken at no cost to the landowner.
The large birds with glossy, purplish-black feathers are part of the crow family.
They could be differentiated from other birds, such as magpies, by their larger size, distinctive"kaah" call, slow wing flap and wariness of people.
Rooks were introduced to New Zealand from 1862 to 1873 to control insects, and their population flourished and spread.
A rook sighting should be reported as soon as possible, and would be sent directly to the council’s biosecurity team. — Allied Media
