With breeding season underway, there are concerns rooks may become a problem on farms in the Waikato.
According to the Waikato Regional Council, rooks are "one of the most destructive farm production pest birds in the world" and populations are found in e Poi/Matamata, Cambridge/Hamilton and Mangakino to Taupō.
Andrew McConnell, Waikato Regional Council biosecurity officer, says the birds generally build their nests in pine or eucalyptus trees.
"They feed on newly sown crops and destroy paddocks by tearing them up in search for grubs," McConnell said on Thursday.
"A large rook population can completely destroy entire paddocks. It’s definitely not something we want to be seeing here in our region."
The species was introduced to New Zealand in the 1860s to control insect pests, and the largest colony ever found in the country was nearly 1000 nests, the council said.
The Waikato Regional Council has been managing rooks since 2002 and the population in the region is now estimated to be less than 50 birds.
Last year five rookeries were found and controlled, three in Mangakino and two in Matamata. A rookery in Hamilton was also destroyed by a storm and abandoned, the council said.
McConnell said finding rookeries isn't an easy process.
"It’s a bit like looking for a needle in a haystack for them, which is why we need landowners to give us a call when they see rooks."
He said farmers should call the regional council if they find the birds, rather than try and get rid of them themselves.
"We don’t want to scare them; it becomes tricky locating rooks once they have been spooked."
