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Large Island Declared Rat-Free in Biggest Removal Success (nationalgeographic.com)
An anonymous reader shares a report: A remote, freezing, salt-spray lashed paradise for wildlife has been completely cleared of rats in the largest rodent eradication of all time, the South Georgia Heritage Trust (SGHT) announced this week. Rats are smart, adaptable, and hungry. For all these reasons, they can be incredibly voracious predators when people accidentally introduce them to remote islands, where the local animals lack evolved defenses to rodents. They have flourished even on an island as harsh and cold as South Georgia, which is so far south that it hosts penguins, elephant seals, and fur seals, as well as massive permanent glaciers.
"There are no trees, there are no bushes. All nest on the ground or underground in burrows," says Mike Richardson, Chairman of the SGHT Habitat Restoration Project Steering Committee. Such nests are easy pickings for rats. The rats -- brought to the island by whalers and sealers as early as the late 18th century -- ate the eggs and vulnerable chicks of seabirds, including albatrosses, skua, terns, and petrels. They also threatened two birds with extinction that are found nowhere else in the world: the South Georgia Pipit -- a tiny speckled songbird -- and the South Georgia Pintail, a brown duck.
The rat eradication was a massive, arduous undertaking, costing more than $13 million and taking nearly a decade. More than 300 metric tons of poison bait was dropped on the island by helicopter in three separate trips during the Austral Summers of 2010-2011, 2012-2013, and 2014-2015. Poisoned rats tend to head underground to die, Richardson says, limiting the damage caused to birds like gulls that might have otherwise eaten the poison-tainted carcasses.
"There are no trees, there are no bushes. All nest on the ground or underground in burrows," says Mike Richardson, Chairman of the SGHT Habitat Restoration Project Steering Committee. Such nests are easy pickings for rats. The rats -- brought to the island by whalers and sealers as early as the late 18th century -- ate the eggs and vulnerable chicks of seabirds, including albatrosses, skua, terns, and petrels. They also threatened two birds with extinction that are found nowhere else in the world: the South Georgia Pipit -- a tiny speckled songbird -- and the South Georgia Pintail, a brown duck.
The rat eradication was a massive, arduous undertaking, costing more than $13 million and taking nearly a decade. More than 300 metric tons of poison bait was dropped on the island by helicopter in three separate trips during the Austral Summers of 2010-2011, 2012-2013, and 2014-2015. Poisoned rats tend to head underground to die, Richardson says, limiting the damage caused to birds like gulls that might have otherwise eaten the poison-tainted carcasses.
The most common rat poison is warfarin which is also used in humans as a blood thinner to prevent blood clots. Iâ(TM)m not saying there are no unknown negatives but rat poison is relatively safe at low doses and pretty well understood.
300 tons of bait, the actual amount of poison is much lower
You can find all the relevant documents here.
From the environmental impact study of Phase I:
A bait drop of the second generation anticoagulant toxin brodifacoum in cereal-based pellets will be distributed by helicopters using under-slung spreader buckets. This will be supplemented with hand spreading of baits in and around buildings and other areas inaccessible by air. Much of the interior of the island and the south coast will be unaffected by the baiting operations.
A little further in that document:
The baiting operation is likely to have negligible effects also on soil, water and vegetation as the toxin is not soluble and will break down to harmless products over a period of several months to a year. Similarly, effects on the marine environment are likely to be negligible due to the small amount of bait entering the sea and rapid break up and dispersal of the bait.
The eradication of the two reindeer herds on South Georgia is currently under consideration by the Government of South Georgia and the South Sandwich Islands, which has responsibility for this issue. Secondary poisoning due to feeding on poisoned carcasses is most likely for brown skua, snowy sheathbill and northern and southern giant petrels. Such losses should be sustainable at the population level, and numbers are predicted to recover on a scale of years.
And from the final report, this paragraph is interesting:
Over 4,600 inert devices, including chewsticks and tracking tunnels, were deployed and checked as part of the survey. The very best rodent detection experts were also brought in especially: three highly trained 'sniffer' dogs and their two skilled female handlers. In an incredible feat of endurance and teamwork reminiscent of Sir Ernest Shackleton’s epic crossing of the island just over a hundred years ago, the handlers walked a total of 1608km, with the dogs covering a total of 2420km, searching for signs of rats. This distance, roughly the equivalent of a return trip from London to Dundee, is all the more impressive given the rugged and challenging terrain of South Georgia.
Well, it depends on the poison, doesn't it?
In this case the pesticide used was brodifacoum -- a chemical analog of the anticoagulant warfarin. The reason brodifacoum is used in this application is that it is a large molecule that breaks down rapidly in the environment -- residue is undetectable after 100 days. The rapid breakdown in soil meaans that there is low potential for bioaccumulation or tolerance development. On the other hand repeated treatments are necessary.
This is why the eradication was so expensive. Had they tried this 100 years ago they'd have used thallium sulfate. Since pretty much all thallium compounds are toxic, fewer retreatments are needed, making thallium cost effective, if you don't count the side effects.
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It's not really a poison per se.
It works by making the rats unable to clot blood, meaning if they start bleeding, they die from loss of blood. But there's more, the "bait" contains both the anticoagulant AND some normal food, usually grain with lots of fiber, designed to have lots of sharp edges. The rat eats this mixture, the grain causes internal bleeding and the anticoagulant makes it impossible for the bleeding to stop.
Neither of the components of the poison are immediately dangerous to people and should you actually ingest it, it's easily treated.
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It is true that the term did not exist until the 20th Century, but Darwin actually formulated the concept, and the rabbit invasion of Australia that occurred soon after 24 wild rabbits were released there in 1859 attracted a lot of attention.
Of course the rats were not introduced intentionally. Neither were tumbleweeds which came from Ukraine (probably in wheat seed shipments) and were first recorded in the U.S. in 1877. Nor the various invasive ant species (fire ants, crazy yellow ants, etc.) plaguing many parts of the world. Simply having people travel about without careful decontamination of belongings has created a lot of invasive introductions.
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