A predator plague that will pose a serious threat to our endangered native wildlife is being predicted by scientists this autumn.
High levels of seed production ('mast') in our beech forests is expected to trigger a rodent and stoat explosion later this year. When seed supplies run out these predators will turn on endangered birds such as mōhua, kākā, kea, whio and kiwi along with other at risk species like bats and land snails.
To protect our native wildlife the Department of Conservation (DOC) is implementing the 'Battle for our Birds' predator control programme. DOC will extend the South Island forest areas targeted for aerial protection with biodegradable 1080 pesticide and boost ground based trapping networks.
What is a forest or beech 'mast'?
Mast events are prolific flowering bursts among forest trees, like beech, over spring and summer. This flowering in turn leads to a bumper seed fall in the following autumn and the widely available seed on the forest floor drives a rapid increase in rat and stoat numbers.
Rats and stoats both prey on native species and the surge in the predator population puts vulnerable natives species under extreme pressure, particularly during the spring when birds are nesting and raising chicks.
View the predator plague cycle to see how the beech mast increases predator numbers and how predators turn to birds for food.
Watch a video
This short video explains the impact of a beech mast cycle on predators and native species.
Where is this a problem and what species are at risk?
There has been heavy forest flowering reported in the North and the South Island although it is most pronounced in the widespread beech forests in the South Island backcountry.
As a result the Department of Conservation (DOC) has identified a number of key threatened species in South Island beech forest areas that are at high risk later this year from a potential rodent and stoat plague.
South Island populations targeted for additional protection include two types of kiwi (great spotted kiwi and Haast tokoeka), yellowhead/mōhua, orange fronted parakeet/kākāriki karaka, kea, kākā, blue duck/whio, rock wren, long and short tailed bats/pekapeka and powelliphanta land snails.
Get information on all at risk species that have been targeted for protection.
A wide range of other forest birds including fantails, robins, tūī and kererū, along with lizards and insects like weta, will also benefit from the temporary knock back of rats, stoats and possums. Key forest food sources such as fuschia, mistletoe and rātā will also thrive without pests.
In the North Island DOC is also planning regular protection operations to support vulnerable populations of brown kiwi, blue duck/whio and long-tailed bats/pekapeka.
View maps detailing the planned areas for protection and the populations at risk.
How big is the threat?
A widespread rodent and stoat plague in South Island beech forests would put some of our most threatened bird species such as yellowhead/mōhua and orange-fronted parakeet/kākāriki karanga at serious risk of extinction.
It’s been estimated that, with no pest control response, we might lose about 75% of the remaining mōhua population - or more than 3500 birds.
In 2000 a widespread beech mast and resulting predator plague caused the local mōhua population in the Marlborough Sounds to go extinct.
Orange-fronted parakeets in Canterbury beech forests also took a big hit in 2000 with one population lost from the Hurunui North Branch and an 85% decline in the Hurunui South Branch population.
A total of just 200-400 of these birds now remain in three beech-clad valleys - the Hawdon and Poulter valleys in Arthur’s Pass National Park and Hurunui South Branch in Lake Sumner Forest Park.
When will DOC know that rat numbers are rising?
The flowering appears to be very widespread and there are some early localised reports of elevated rat numbers. But the full extent of the seed fall and the wider impact on predator numbers is yet to unflold.
Over the summer months DOC staff will be measuring the amount of seed produced and the autumn seed fall to gauge the final scale of the beech mast and food available for mice and rats.
Field teams are also keeping a close eye on rat and stoat tracking stations in at risk forests.
How does DOC plan to protect at risk populations?
DOC routinely uses traps and other ground based techniques such as bait stations to control rats, stoats and possums. Traps and bait stations will continue to play a significant role in protecting threatened populations such as whio/blue duck in Tongariro, mōhua in the Eglinton valley and kiwi in the West Coast..
However research has shown that rapidly rising rat numbers produced by mast conditions can overwhelm trap networks. Ground based control on its own does not protect threatened bird and bat populations from these predator explosions.
The study of pest control techniques during two localised rat plagues in 2006 and 2009 through DOC’s Operation Ark multi-species protection programme showed that aerial 1080 treatment knocked down rat plagues to near zero levels where ground based methods were not effective on their own.
DOC is prepared to significantly expand its aerial 1080 operations in South Island beech forests in 2014/15 to respond to rising predator numbers.
How effective is 1080 in countering these predator threats?
Permanently eliminating rats and stoats is not currently feasible but research during past mast events has shown aerial 1080 to be the most cost effective tool for quickly knocking down predators over large areas and in difficult terrain.
Aerial 1080 has been shown to suppress rodent plagues to near zero density levels for up to five months. Tracking results indicated it can also kill more than 95% of stoats through secondary poisoning.
For example, aerial 1080 used in the Dart Valley in Fiordland during the rat plague in 2006 resulted in 80% of mōhua surviving whereas in uncontrolled areas only 10% survived.
At Ōkārito on the West Coast aerial 1080 timed to target rats after a beech mast in 2011 doubled the nesting success of kea. Kea pairs in the treated area produced about four chicks each whereas those in the untreated area produced only one due to stoats and possums preying on nests.
As well as being fast and effective over wide areas, aerial 1080 operations cost approximately a third the cost of most ground based alternatives.
Get more information about the use of 1080 for pest control.
How much land managed by DOC is currently treated with aerial 1080?
Pest control cycles vary but over the past five years DOC has treated an average of about 140,000 hectares with aerial 1080 specifically to protect forest ecosystems and native species. This represents about 2% of the 8.7 million hectares of public conservation land which is managed by DOC.
TBfree New Zealand also carries out aerial 1080 operations over an approximate 300,000 additional hectares of public conservation land to protect dairy herds from possums infected with bovine tuberculosis.
Together these combined aerial 1080 programmes cover about 440,000 hectares or approximately about 5% of all public conservation land managed by DOC.
View an infographic showing facts and figures about 1080 in New Zealand
How much more land is DOC preparing to treat with aerial 1080 as part of its Battle for our Birds beech mast response?
The exact scale of DOC’s aerial 1080 programme in the coming year will depend on whether predator populations reach levels which trigger a response but, if required, DOC is ready to increase its aerial 1080 protection in the South Island by about 500,000 hectares.
This together with TBfree New Zealand's planned programme would result in a total of about a million hectares of public conservation land being treated with aerial 1080 in 2014/15 – about 12% of the land managed by DOC.
To increase its on-going protection for native species DOC is also committed to increasing its aerial 1080 programme by about 50,000 hectares a year for five years. This means DOC itself will be supporting the 2014 beech mast response by routinely treating about 400,000 hectares of public conservation with 1080 by 2019.
What is this expanded programme expected to cost and how will DOC pay for it?
This new Battle for our Birds programme is expected to cost about $21 million over five years. It is a priority project for DOC and will be funded out of the Department’s existing budget using efficiencies gained from improved pest control techniques and co-ordination of operations.
View a brochure about Battle for our Birds
Battle for our Birds: Beech Mast 2014 brochure (PDF, 2,100K)
View information that's in the brochure on web pages:
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