Visiting island predator eradication projects provides insight into the challenges they face and the technologies and methods that underpin successful predator control.
During August we began an extensive research trip to visit and gain a better understanding of international predator control and eradication projects, especially the range of factors that act to both enable and disenable these initiatives.
There is a spectrum of projects, all on islands, that target a range of mammalian pests and predators using both trapping and toxins for control.
Our first destination was Lord Howe Island during August about 600km off the coast of New South Wales, north of Sydney. Here, an ambitious project to eradicate both black rats and mice using an aerial distribution of toxin is being planned. If successful Lord Howe Island will become the largest inhabited island from which rodents have been removed.
The Lord Howe Island community have previously removed pigs and cats from the island using trapping and hunting. Since then there has been a tremendous response in both the distribution and abundance of nesting seabirds. Lord Howe is the only nesting site of the Providence Petrel and today these can be seen returning to their nesting burrows as large flocks of birds.
Although planned for 2018, the aerial distribution of toxin will now go ahead in 2019 after the project received a key approval to proceed. As a result of community concern the toxin will only be aerially spread over the steeper parts of the island with 21,000 poison bait stations being used to remove rodents from the inhabited parts of the island.
Our second destination, in September, will be the Isles of Scilly located at the southern tip of the British Isles. Here on the small island of St Agnes, inhabited by fewer than 100 people, Brown rats were successfully eradicated several years ago using a ground based poison operation. Like Lord Howe Island, one of the principal benefactors of this project has been nesting seabirds.
October will see us visit the Orkney Islands where a project to eradicate stoats using trapping has recently begun. Although a native mammal in the UK the stoat has not previously been present on the Orkney Islands and large numbers of ground-nesting waders are now under threat from this recent introduction of a new predator.
The Scottish Hebrides has also been the focus of a very wide ranging trapping programme over recent years to remove the introduced American mink. These escapees from a failed fur farming industry have not only had big ecological impacts on native fauna and ground nesting birds they have also had big economic effects on fish farming.
American mink live a highly aquatic life and are skilled hunters both in and out of the water. Evidence shows the project is now needing to trap the last few individuals and that the population is likely no longer able to breed.
The Hebrides also demonstrate again how the introduction of a predator for the biological control of pests can go awry. Hedgehogs are not native to the islands but were released to control garden pests, however as with mustelids in New Zealand they have not limited themselves to this role and now also prey on the ground nests of vulnerable populations of waders.
While the obvious connection between these island predator control projects is the removal of the pest population, we are particularly interested to learn more about plans to keep them from returning. Predator monitoring on islands that needs constant monitoring at the landscape scale is becoming an increasingly demanding issue as the number and size of islands from which predators have been removed continues to increase.
The Orkneys demonstrate how predators can establish on remote inhabited islands as an unintended consequence of trade and travel. Lord Howe Island and the Scottish Hebrides demonstrate how expensive it is to remove established populations of invasive predators as these projects are both in the order of NZ$10 million each. This questions the view that toxin based eradications are automatically more cost effective than trapping. They are clearly also investments that need protecting with effective surveillance technology and methodologies.
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