3.5 Use of 1080 to control other pests
While 1080 is used primarily against possums, it is increasingly used to target other pest species, sometimes as part of possum operations. Carefully selecting the time of aerial operations can reduce predators such as rats and stoats, just before birds start nesting. This can have significant benefits, and leads to improved survival rates as described in Chapter 5. Stoats are killed through secondary poisoning, by eating poisoned rat carcasses, but can re-invade within 2-4 months of an operation. Aerial operations can often, but not always, achieve good rat control for about 3 months or longer. The consequence of failing to control predators is often a steady decline in bird numbers.
Possums and other predators controlled using 1080 are not the only threat to native forests. In many places, selective feeding by possums on forest trees is made worse by the browsing of deer and goats on ground vegetation, seedlings and shrubs. Research over many decades has clearly shown that introduced deer species and goats have a major impact, by stopping the normal regeneration cycles in forests. Under the combined assault of deer and goats from below, and possums from above, many palatable plants gradually or rapidly disappear from forests. These other pests can be killed as a consequence of aerial operations, and in some places, where they are causing significant damage, other control methods are used. For example, high densities of goats, deer, wallabies or other browsers can be targeted by using 1080 in a paste form applied to leaves.
Rabbit control
Although the focus on 1080 use is usually on possums, it has long been an important toxin in the battle to reduce rabbit numbers. As noted in the next section, its first use in Australia was in rabbit control operations. In New Zealand, 1080 paste baits are used for rabbit control, particularly on and around farms. Various baits and cereal pellets are also used for larger scale control operations on rabbits.
The susceptibility of New Zealand's native forests to introduced pests
Why are our forests so susceptible to possums and browsing mammals that have little impact in their native countries? The answer lies in our unique natural history. As they drifted away from the nearest landmasses, these islands continued evolving for over 60 million years without the browsing pressure of mammals. No other large landmass on Earth has had such a history. Hence, before the arrival of the first voyaging Polynesians about a thousand years ago, the only land mammals in New Zealand were three species of small bats, one of which is now extinct. Our native plants have co-evolved with browsing and grazing birds, and developed defences and strategies to overcome that impact, or to benefit from the birds, by pollination, seed dispersal or habitat maintenance. Our native plants have few of the defences against browsers, such as thorns, tough leaves and plant poisons (such as fluoroacetate), which evolved in countries with mammalian browsers and grazers. Nor have they developed pollination or seed dispersal mechanisms that could exploit mammalian behaviours. They are, therefore, particularly defenceless against the onslaught from introduced browsing and grazing mammals. To make the problems worse, many of the introduced animals found themselves in an environment without the controls that normally limited their populations (droughts, extreme winters, fires, predators, competitors, diseases and parasites).
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