Invasive non-native species and why we intervene

To be blunt, invasive non-native species damage our environmental economy and health.  Stan Whitaker, SNH’s Policy & Advice Manager for Ecosystems & Biodiversity, explains further.

Uist wader project worker lamping for hedgehogs on the South Uist machair, Western Isles Area. ©Lorne Gill/SNH

Uist wader project worker lamping for hedgehogs on the South Uist machair, Western Isles Area. ©Lorne Gill/SNH

In conserving threatened species, we have to focus our limited resources on those where we can make the most difference.  This often means dealing with invasive non-native species INNS) that threaten native species. The following short blog post outlines some of the work we are currently involved in.

Not all non-native (alien) species are damaging. Many species that have been introduced to our gardens, fields and landscapes are now an important part of Scotland’s diversity and underpin many of our primary industries. However, a minority have serious negative impacts on native Scottish habitats, our health or our economy. We refer to these species as invasive non-native species

The most challenging invaders tend to be land mammals, aquatic plants and invertebrates.  SNH leads on invasive non-native species on land and our top priorities are to identify how these species invade and act quickly to prevent their establishment and spread.

Here we take a brief look at our work to control three invasive non-native mammals in particular. We prioritise our funding for large-scale eradication and control where it will have significant long-term benefits for the natural heritage.  The projects outlined below all have the potential to deliver real benefits to species, communities and local economies.

Hebridean Mink

The main objective of the Hebridean Mink Project is to eradicate American mink totally from the Outer Hebrides, preventing further significant disturbance and losses to our internationally important populations of ground nesting birds, and creating the conditions for native species to recover.


Arctic tern nesting. ©Lorne Gill/SNH

The conservation of the local and migrant bird species found throughout the Outer Hebrides will undoubtedly ensure a brighter future for the tourist industry here. As mink numbers have decreased the number of breeding tern colonies has increased throughout the lslands. Anglers and fish farms will also benefit, as the considerable damage to farmed fish and young wild fish stocks by mink will cease.

American mink predation on domestic poultry has been so severe previously that many people had given up. However, many local crofters, encouraged by the positive results of the project are already keeping chickens and ducks again.

Hedgehogs in the Uists

Our Uist wader research project aims to protect ground-nesting birds from egg predation by introduced hedgehogs. The project was established in 2000 in response to concern about declines in the internationally important wader populations which nest on the islands of North Uist, Benbecula and South Uist (see more on our website). These ground nesting birds nest in high densities on the islands and have declined over the past 25 years. Research in the 1980s and 1990s showed that this was largely due to predation of their eggs by hedgehogs.

Dunlin in breeding plumage, South Uist. ©Lorne Gill/SNH

Dunlin in breeding plumage, South Uist. ©Lorne Gill/SNH

In 2011, the project started a new phase: a four-year research programme into the islands’ breeding wader populations. The project monitored the outcome of over 1000 nests, gathering information on the factors affecting breeding success, and demonstrating that hedgehogs are having a significant impact on wader populations. Alongside the research, efforts continued to prevent hedgehogs re-colonising areas already cleared. We have developed the techniques required to capture hedgehogs, and are now in the process of investigating sources of funding for a large scale removal project.

Stoats in Orkney

Stoats were first seen in Orkney in 2010 and since then the population has become well established. They are now widely distributed throughout Mainland Orkney, Burray and South Ronaldsay.

Stoats are accomplished predators and pose a very serious threat to Orkney’s wildlife, including the native Orkney vole, hen harrier, short-eared owl and ground nesting birds.

Short-eared owl. ©Lorne Gill

Short-eared owl. ©Lorne Gill

The Orkney Native Wildlife project tackles the threat posed by stoats. Our aim is to develop a project to safeguard Orkney’s ecology by removing stoats, and to prevent the stoat population from spreading to Orkney’s other islands.

SNH often works in partnership, and tackling invasive non-native species is a good example of where this tactic can work very well. In many cases we encourage action by others, rather than taking direct action ourselves, by supporting projects which involve the public and land managers in tackling INNS in a coordinated and cost-effective manner.  Further examples of this collaborative approach are our work on Saving Scotland’s red squirrels and the Scottish Invasive Species Initiative, an ambitious proposal which aims to control mink and invasive plants across a 29,500 km² area in the north of Scotland.

This is by no means the full extent of our work across Scotland in relation to invasive non-native species, but perhaps gives an insight into the approaches we take and the challenges we face.

See the SNH website for further information on non-native species.

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