Today’s photo is of a mōhua/yellowhead, a small insectivorous bird endemic to the South Island of New Zealand.
Once abundant in the South Island the population declined dramatically with the introduction of rats and stoats. Today they have vanished from nearly 75% of their former range.
Recent pest control targeting rats and stoats has helped to protect mōhua in 10,000 hectares of beech forest in the Catlins. Results shows that mōhua have increased to the highest level recorded since the population suffered a big decline about 14 years ago.
Rat and stoat levels will be monitored closely with the predicted large beech mast this autumn to determine whether a pest control response is needed later this year as part of DOC’s Battle for our Birds programme.
Today, we’re going to have a closer look at what we’re going to do about it…
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.
Our whio are nationally vulnerable, with less than 3,000 remaining
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.
South Island beech forest
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.
Aerial 1080 timed to target rats after a beech mast in 2011 doubled the nesting success of kea
As well as being fast and effective over wide areas, aerial 1080 operations cost approximately a third the cost of most ground based alternatives.
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.
The Battle for our Birds doesn’t stop at protecting our birds, but other species such as our giant snails/Powelliphanta, which are among our most threatened invertebrates
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.
The heaviest beech forest seedfall in more than a decade is predicted this year. It is expected the increased seedfall will lead to an explosion in the numbers of rats, mice and stoats, who will turn to our native birds for food once the seeds disappear.
Beech trees generally seed every four to five years but weather conditions over the last two summers—a cool summer followed by a warm one—appear to have triggered a bumper seed or “beech mast” event. Intense and widespread flowering was witnessed throughout North and South Island beech forests during spring and early summer, prompting the need for urgent action.
Past experience has shown that when a beech mast occurs, it leads to a dramatic rise in mice and rat populations, who feast on the plentiful seed all winter. To give you an idea of how quickly they can multiply, a single female rat can potentially produce 10 offspring every eight weeks—that’s a lot of rats!
An explosion in rodent numbers leads to a sharp rise in the number of stoats, which also pose a lethal threat to many species.
Rat eating fantail chicks at nest
In spring, when the seed runs out, germinates and rots, these predators will then prey on native birds and their eggs, as well as other critically endangered critters such as native bats and snails.
This will put some of our most threatened species at risk of extinction including:
Kea and tākahe are also at risk of being preyed on by stoats.
Landcare Research estimates that 25 million native birds die through predation every year in New Zealand and the beech mast is expected to make the situation much worse. For example, there are only 200–400 wild orange-fronted parakeet left and during the beech mast that occurred in 2000, 85% of the southern population was wiped out due to the rat plague.
85% of the southern population of orange-fronted parakeets were wiped out during the beech mast that occurred in 2000
DOC staff will monitor the amount of seed produced this summer and seedfall in the autumn. Rat tracking will also take place in February and May.
DOC scientist Graeme Elliott says, “So far we’ve only been able to get a visual idea of the issue. We’ve seen lots of flowering during the spring, which caused huge clouds of pollen above the forests.
“The seeds are developing at the moment but in February we’ll be able to start counting them to get a better idea of the scale of the mast. We do this by shooting down branches at the top of the tree, where they’re exposed to the sun and produce the most seeds.
“The best indicator will be the rat tracking. If the numbers dramatically increase or are already high in February, we’ll know we’ve got a big problem to deal with.”
Last night the Minster of Conservation, Dr Nick Smith, announced DOC’s plans to respond and launched our largest-ever species protection programme called ‘Battle for our Birds’. We’ll talk about this in more detail over the coming weeks. For now, you can learn more about it on the DOC website: www.doc.govt.nz/battleforourbirds.