Last colony of “invasive” Black Rats to be exterminated in the UK

John Dixon sent me this article on a project to exterminate Rattus rattus from some Hebridean islands (off of Scotland) which has generated some controversy among bird and mammal fans alike, seems like there is rather limited evidence to suggest the rats are a problem at all, they’ve been there for a very long long time and may well be woven into the ecosystem, while if anything is harming the seabirds its the lack of fish. Still, its not like the EU to throw money at a project that will end in failure….

Some of you may remember this fun report of a trip last year to see them. Save the rats I say!



  • vdinets

    Rat eradications on other islands have resulted in huge increases in seabird numbers. Rats are, of course, a part of the ecosystem now, but it’s an artificial ecosystem very different from the original one, and much less productive. As for their numbers being kept low by cold winters, this is one control mechanism very likely to stop working in the near future.

    • Mike Richardson

      It’s not cold winters that keep the Black Rat population in check but rather a lack of food once the birds leave and the vegetation dies off.

      The seabird population has thrived alongside the rats for hundreds of years and previous research has found that even in summer the birds make up only a small percentage of the rat diet. Lack of suitable nesting sites and a decrease in fish (caused by overfishing, pollution and climate change) are more significant barriers to seabird population growth on the Shiants.

      While I’m usually the first to advocate the removal of invasive species I believe further research is needed before such a large amount of money is spent eradicating the rats. In the meantime Scottish Natural Heritage would be better off concentrating on saving the last hundred Scottish Wildcats (along with another 101 more pressing conservation issues in Scotland).

      • vdinets

        Hundreds of years? The sources I’ve seen claim that the rats were accidentally introduced as a result of some shipwrecks c. 1900.
        The two species suffering the most from the rats are Manx’ shearwater and European storm-petrel. Both nest in burrows and talus slopes, so they are unlikely to face nesting site shortage. And storm-petrels feed on plankton rather than fish.

  • Jon Hall

    I don’t know much about this case but do think on what little I’ve read that some more evidence on the benefits would be useful before spending so much money that could be well spent elsewhere. Getting rid of invasive species is often a good thing, it isn’t always, especially when they’ve been around for a long time: it depends on the species and the ecosystem. Killing Dingos in Australia has led to increases in Foxes which are generally seen as worse for the native fauna True its hard to imagine how killing the rats might harm the ecosystem (rather than do little to help it) but its got to be worth thinking through. Maybe this has all been well studied… but it sounds like it hasn’t. So it could be like the old lady in the song who swallowed the fly… with hindsight she’d have let the fly be, and stayed off the expensive and destructive bird, cat, dog etc project. But perhaps the EU funded that too.

    • vdinets

      Rat eradications are nothing new; they’ve been conducted on dozens of islands and there’s never been any negative effect on anything native. If there are also introduced cats and foxes present, it can undermine their populations as well by removing the winter food source, but I don’t know if this is the case on the Shiants.

  • Mike Richardson

    I don’t think anyone really knows when Black Rats first colonised the Shiants. They are thought to have lived in mainland Britain from as early as the 1st century but numbers started to decline around the 18th century through competition with the Brown Rat. It’s a reasonable to assume the Shiant Black Rat population is much older than 100 years.

    Manx Shearwaters and European Storm-petrels do not nest on the Shiants and I’ve not seen any evidence to suggest that they ever have. The initial call to eradicate the rats was due to a perceived threat to nesting Puffins and Razorbills, both which thrive on the island. I guess shearwater and storm-petrel s may be attracted to the island once the rats have gone but don’t they rely heavily on rabbit burrows to breed? There are no rabbits on the island. In fact there are no humans, foxes, cats or any other mammals living on the Shiants, apart from sheep.

    • vdinets

      Both shearwaters and storm-petrels have lived on islands off Scotland long before rabbits were introduced. Shearwaters can dig their own burrows, and s-petrels can use theirs or nest in talus slopes.

  • mattinidaho

    I suggest Will Stolzenburg’s excellent book “Rat Island” which is a good account of clearing invasive rats off islands. The island so named “Rat Island” — in the Aleutians — had become a biological desert. Since the rats have been removed, the surveys are showing huge increases in sea birds, nesting, etc. It is a completely different island (and now has a new name, Hawadax).

    It is also very expensive, so ideally rat eradication would be undertaken in areas where it will have the most benefit.

    I also hear more conservation biologists questioning the notion that invasive species are always bad, in every circumstance. I think it more nuanced than that. Sometimes the “cure” for invasives is worse than the disease.

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