Rat numbers have soared to record winter levels in the Waitakere ranges' largest conservation project and emergency efforts are underway to protect endangered kōkako and other native wildlife.
This season’s rat tracking results, at 32 percent, have edged past those of the previous mast year in 2014, and Forest & Bird warns things are going to get even worse as the weather warms.
"Forest & Bird staff and volunteers have been preparing for this predicted boom in rats but we're still deeply concerned for the native species in the ranges," says Forest & Bird’s Ark in the Park manager Gillian Wadams.
“These numbers are well above the five percent that allows birds to survive and breed, and far higher than the one percent needed for all kōkako chicks to be safe from rats.
“We fear stoat and weasel numbers are much higher than normal too. We’re heading into bird breeding season, so it’s important we get these predators under control now.
“After the last mast in 2014, it took us about a year to get rat numbers down again and we still have not got back to pre-2014 levels.”
“We’re worried about all our species being hit by this upsurge in rats, and kōkako in particular as they are especially vulnerable to rats and stoats,” Miss Wadams says.
Three Forest & Bird staff members and about 400 volunteers carry out intensive predator trapping and rat baiting across the 2270 hectare Ark. Bait is being put out more often and in larger quantities to try to protect native species from booming rat and stoat populations.
Predators also hammer native bats, frogs, geckos and insects and reduce forest regeneration by eating seeds and young plants.
Native trees fruit extremely heavily in an event known as a mast. These events once gave a boost to native birds, but mast years now result in a massive increase in rats and stoats.
Climate change adds to the problem, as masts are becoming more frequent and rats are able to breed all year during mild winters.
“We’re doing everything we can, but mast years seem to more frequent with climate change, so rats, stoats, and possums are an increasing risk to our native wildlife,” says Ms Wadams.