The impact of invasive mammals in Britain

There are around 200 known invasive non-native plant and animal species in Britain and this number is increasing. A number of these are invasive mammals – and they can have a devastating impact on our native wildlife.

What are invasive species?

Mammal Society Vice-Chair Kate Hills, explains “Invasive Non-Native Species are plants and animals which have been moved from their place of origin and, accidentally or intentionally, brought to Britain by humans. Their introduction has a negative impact on the environment, the economy and sometimes health.”

Where the impact of invasive species is negative, it can be devastating

Kate, also Invasive Non-Native Species ecologist for South West Water, explains “Perhaps the best example of an Invasive Non-Native Species, is that of American Mink. The American Mink were originally brought to fur farms in Britain from North America and, having subsequently escaped (or been misguidedly released), were responsible for decimating the water vole population, making it the fastest declining mammal in Britain.  American Mink have also had a significant impact on the population of seabird colonies, particularly black guillemots.”

Naturalised and native species may be invasive

Many people may not be aware that some mammals considered to be native in Britain, such as grey squirrels aren’t actually native. They were introduced, a long time ago, but can still have a negative impact.

Grey squirrels were introduced from the USA over 100 years ago and are now widespread in England and Wales, central Scotland and the eastern half of Ireland, and still spreading. Grey squirrels are serious pests and have an economic impact on forestry, especially stripping the bark of thin-barked species such as beech and sycamore, increasing the risk of fungal infections. They are also carriers of the Squirrelpox Virus which is fatal to red squirrels and have had a devastating impact on our native red squirrels. The grey squirrel is a European Union species of concern.

Some native species, such as hedgehogs, are native to parts of Britain but, where they have been moved from the mainland to Britain’s islands, they are invasive and can cause problems by feeding on wild bird eggs, as in the Isles of Scilly or the Hebrides islands.

Can native species have a positive role?

In a limited number of cases invasive species can have a positive impact on our environment, for example as a food source. Pine martens, feed on grey squirrels because they are larger and less agile than red squirrels thereby keeping numbers of grey squirrels down and allowing red squirrels to thrive.

In contrast, wildcats are a species that have suffered dramatic declines due to an invasive species. The single biggest threat to the Scottish wildcat population in Britain is the domestic cat. Wildcats can successfully hybridise with the domestic cat, which threatens the genetic purity of the species. Scottish wildcats are unique to Britain and only found in Scotland.

What can you do to help?

You can help the Mammal Society to find out more about invasive species by recording sightings of all mammals, invasive and native species, using our tracker app or one of the other methods detailed on our website http://www.mammal.org.uk/science-research/record-submission/ . 

In addition to the species you would normally expect to see in our landscape, the Mammal Society is asking people to keep a special look out for raccoons and other invasive animals that people have been introducing to the UK as pets, and which have caused significant problems for native species in continental Europe.

Anyone who is interested in this topic and would like to hear more should come along to the Mammal Society and GB Non Native Species Secretariat Invasive Mammals Conference on Friday 9 and Saturday 10 November 2018 at the Arup offices on Fitzroy Street in London, sponsored by Thames Water and South West Water. Full details will appear on our website shortly.

For more information on any of the mammals listed above (and many more) visit the Mammal Society website http://www.mammal.org.uk

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