The Department of Conservation has today begun its Battle for our Birds pest control in the Maruia Valley area near Lewis Pass to protect native wildlife from rat and stoat plagues.
August monitoring showed rat levels nearly doubled in the area between May and August, from 37% to 67%.
Preliminary estimates indicate rat densities of at least 6-9 rats per hectare in the Maruia Valley pest control area in August (half to three quarters of a million rats). These are predicted to increase and could reach up to 20 rats per hectare by November if not stopped with pest control.
The rat surge would in turn fuel a stoat plague from summer. With plentiful rodents to feed on stoats produce more young than usual.
The aerial 1080 pest control covers up to 85,000 hectares in the Maruia Valley, and Glenroy, Upper Grey and Inangahua river catchments.
The pest control is needed to protect vulnerable populations of mōhua/yellowhead, whio/blue duck, long-tailed bats/pekapeka, kea, kākā, rock wren/tuke, Powelliphanta snails and kākāriki/parakeet.
Today non-toxic baits are being aerially-applied to encourage rats and possums to eat baits containing biodegradable 1080 pesticide that will be sown at a later date when weather conditions allow.
The operation is part of DOC’s Battle for our Birds predator control programme to protect native species from rising predator numbers fuelled by an exceptionally heavy beech seed-fall in many South Island forests.
DOC Greymouth Conservation Services Manager Shane Hall said the rapid rat rises resulted from a heavy autumn beech seed-fall, with red beech trees in the Maruia Valley having produced around 4300 seeds per square metre and mountain beech a huge 13,000 seeds per square metre.
“Our aerial 1080 pest control will help prevent vulnerable native species suffering heavy losses from the growing predator numbers during birds’ crucial breeding season.
“If we don’t act a small mōhua population and giant snail species would be at risk of extinction. We also particularly want to protect a nationally important population of long-tailed bats in the area.”
Aerial 1080 pest control enables large-scale protection in difficult terrain. It rapidly knocks down rats and stoats are also substantially reduced through their eating poisoned rodent carcasses.
The pest control also reduces possums to low numbers. Possums prey on native birds, their eggs and giant snails and cause browsing damage to native vegetation, including highly vulnerable mistletoes in the Maruia Valley area.
Fast rising predator numbers can overwhelm trapping networks and ground control on its own cannot protect vulnerable native wildlife from rat and stoat plagues triggered by a heavy beech seed-fall, known as a mast.
A mōhua population in the Reid’s Stream area is only just hanging on after it nearly became extinct during a predator plague fuelled by a similar heavy beech seed-fall in 2000.
The Powelliphanta ’Matakitaki’ snail species is thought to only exist on Mount Baldy and it could be wiped out by rats and possums.
Tracks, including the Lake Daniells Track, and some parts of the Palmers Road Conservation Area, Victoria Forest Park and the Lewis Pass Scenic Reserve will be temporarily closed during aerial application of 1080 baits in the Maruia valley pest control area. Tracks will reopen as soon as possible once they are cleared of bait.
The 1080-laced baits will be sown at a rate of 1 kilogramme per hectare.
The Maruia operation is one of 25 confirmed operations that will use aerially-applied 1080 over about 680,000 hectares of conservation land to knock down rising predator numbers fuelled by unusually heavy seeding in South Island beech forests. Seven operations have been completed.
The coordinated Battle for our Birds pest control programme is targeted to protect the most at-risk populations of mōhua/yellowhead, kākāriki/parakeet, kiwi, whio/blue duck, kea, kākā, rock wren, giant land snails and native bats at sites across the South Island.
More information on DOC’s Battle for our Birds pest control operations can be found on the DOC website.