How we decide when to use 1080
IntroductionWe work to make sure our 1080 operations are well-organised, safe and necessary to protect native forests and species.
When monitoring shows native species are in danger from predators, we identify the most effective methods to protect them. We do this by weighing up the control options, based on knowledge of the landscape and the species and predators living there.
1080 is one of the tools we need to use to protect native wildlife. So we work to make sure our 1080 operations are well-organised, safe and necessary.
We also do a lot of work before we make decisions to protect native forests and species. We:
- create long term conservation plans with hapū, iwi, whanau and conservation groups
- work over many years to understand an area’s conservation needs
- identify important ecosystems and risks of species becoming extinct
- prioritise areas for predator control operations
- work with community and government partners to achieve predator control.
Read an example of this process in Cape Brett, Russell on the NZ Herald website.
When is aerial 1080 necessary?
DOC continually monitors native species and predators such as rats, stoats and possums at priority sites on public conservation land. When monitoring shows we need large-scale control of these predators, we need to use 1080. Without it, these predators will drive many of our native species to extinction.
No control method on its own will stop predators from reinvading. So we need to combine the methods we use for the best effect.
Monitoring helps us plan the best use of ground based or aerial methods, or both. Ground based control includes poisoning, trapping and predator-proof fencing. Aerial control on the New Zealand mainland may use 1080 bait distributed from aircraft.
We recommend large-scale control and aerial 1080 as best to use if one or more of these factors are present:
- rat tracking results are showing a population explosion (this is known as an ‘irruption’)
- climate and seed monitoring are forecasting a mast year
- we need to kill predators quickly over large areas (over 1500 ha for rats and 2000 ha for possums )
- there are multiple species of predators in one area
- the area is remote or inaccessible on foot
- ground control is not workable. Learn more in our 'Hold the line' video.
- previous 1080 operations in the area have proved to protect native species
Finding out predator numbers
If predator numbers are too great, they are likely to threaten native species. To find out predator numbers in an area we monitor:
- footprint tracking rates in tracking tunnels
- bite marks on chewcards or waxtags
- capture rates in traps.
Rat tracking rates help us decide when native birds are likely to be under threat. The action we take depends on the time and place, and the species of bird we are protecting.
We know that when multiple predator species are present, controlling only one will not help restore an ecosystem.
Aerial 1080 is very effective because it can vastly reduce populations of rodents, stoats and possums in a few days.
More information on monitoring
Predicting mast years and predator numbers rises
We need to know if the number of predators are going to stay the same or if there is likely to be a population explosion. This depends on forest-type and altitude. In some types of New Zealand forest, predator numbers are high most of the time and need permanent control. Others have periodic boom and bust cycles of rodents and stoats. This is due to a natural cycle of heavy seeding which is called a ‘mast year’.
We use climate modelling to predict forest masts a year ahead. We then monitor seed the following summer to check our prediction and measure any seed present.
When seed is abundant, rats increase rapidly, and stoats follow, feeding on the rats. When seeding finishes, the rats and stoats turn to eating native wildlife, including birds, bats, snails and lizards.
To prevent losing native species we can predict when this abundance is likely to happen and start to plan an aerial 1080 operation. We aim to drop 1080 when rat populations have begun to climb, but before the female stoats have their young the following summer. Unlike rats, stoats only breed once a year. But when there are plenty of rodents to eat, stoats can increase the number of young they give birth to, so their numbers quickly surge.
If tracking tunnel results show rat numbers are not meeting our predictions, we have time to cancel or change the operation.
Using trapping for effective control
Trapping takes much longer than aerial 1080 and needs different methods for each predator species. Rat trap lines need to be spaced about 100 m apart, with no more than 50 m between each trap on each line. Stoat traplines need to be 500-1000 m apart with traps spaced at 100-200 m.
The spacing of bait stations also needs to consider the landscape, the number of predators in the area and the size of their home range . This is the area the animal usually lives in, that it marks as its own. If there are a lot of rats in an area, more bait stations are needed, because their home ranges become smaller.
The frequency of control is important too. Rats need controlling year after year because they reinvade after the control operation and breed rapidly. Possum populations increase slowly, so they need control less often.
More information about trapping
How do we know aerial 1080 works?
We use many techniques to monitor native wildlife. These include tagging, radio transmitters, camera traps, observing nests or roosts and 5 minute bird counts. You can read about them on our biodiversity toolbox pages.
Comparing monitoring data before and after control operations shows us how well our predator control methods are working.
We also monitor native species in areas that have no predator control, to compare the results. Our knowledge is growing year by year as we monitor the outcomes of our predator control work. See the latest results of our control work.
We have monitored taonga species in some areas for over 30 years.