"They'll basically strip the seed out of the ground and you're left with big bare patches.
"So that's one of the reasons we've been so active in trying to control the numbers over the years, because we have seen occasions in which the damage has been quite severe."
The council's rook eradication programme began in the late 1980s and has since reduced numbers of the pest.
"I've got about 116 sites on our database at the moment, which we actually go around to and have a look at with the helicopters," Mr Playle said.
"Last year out of all of those sites we had eight active rookeries so it's not a big number."
Once the surveying in the region is completed, the council's biosecurity team will wait for a fine day to complete baiting.
The baiting is done by an operator suspended on a chain underneath the helicopter.
The bait and toxin are applied with a corking gun into the nest manually.
"So it's not like a blanket operation," Mr Playle said. "It's very precise and we know where all the bait goes. Our operators know the difference between a rookery and, say, a blue-heron nest, so we're only treating the right nests, not at random.
"It's a precision operation."
Mr Playle said that generally most rookeries were found in Northern Wairarapa, but the council had found active ones along Te Ore Ore and Upper Plain roads.
Landowners, contractors, and anyone who knows the location of an active rookery are asked to contact the council with details.
"We are keen to hear from those who might have called us in the past, as well as those finding rooks for the first time," Mr Playle said.
"It's important that property owners don't try to poison or shoot any rooks they find. These are wary birds and will quickly disperse and establish more rookeries."
Council biosecurity officers would control the rooks at no cost to the landowner.
