Mousa SPA
The famous Mousa broch and beach Photo: Tom Churchyard

Mousa is a low-lying island, just 1.5km long, which sits on the 60° North line one mile to the East of the Shetland Mainland. Mousa is well known for its 2000-year-old well-preserved broch and the European storm petrel (Hydrobates pelagicus) colony that return each year to breed in the Broch’s tall stone walls. Now uninhabited (the last family left the island in 1853) Mousa has a long history of human history stretching back as far as the stone age. Managed as a reserve by the RSPB and grazed by Shetland sheep, the island is a haven for wildlife while continuing in its role as part of Shetland’s crofting/farming heritage.

Highlighting the island’s importance for natural heritage Mousa has multiple nature conservation designations, both national and European. The island plays host to important colonies of breeding seabirds, including the UK’s largest storm petrel colony, as well as breeding common seals and other species such as the tiny Shetland wren. Mousa’s mix coastal habitat, wet heathland, mires and grassland, as well as the broch and dry-stone dykes (walls), provide habitats for these animals to live, feed and breed in.

Broch and stone dykes on Mousa, home to the island’s large storm petrel colony Photo: Afra Skene

One of the things that makes Mousa so remarkable as a wildlife haven is the fact that the island is still entirely free of introduced predators such as rats, mice, hedgehogs and stoats, all of whom now live on the nearby Shetland Mainland. Maintaining the rodent-free status of Mousa is particularly vital for the internationally important  European storm petrel population as these tiny seabirds are so very vulnerable to predation and only breed on islands that do not have rats.

European Stormpetrel Photo RSPB Images Alastair Wilson

European storm petrel dapples the water surface Photo: Alastair Wilson (RSPB-images)

RSPB manage Mousa as a nature reserve and have already drawn up a biosecurity plan for the island which details how the risk of introducing non-native species can be reduced. The RSPB warden and Biosecurity for LIFE staff have put in place a surveillance system to monitor for presence of invasive non-native mammal species that could cause harm to the native wildlife. The primary risk species are rats and mice as they can travel easily as stowaways on visiting boats or in cargo/baggage. The main detection methods for these species are tunnels or boxes containing wax blocks that are flavoured to attract a rodent if it were to reach the island, gnaw marks left on the blocks that can be identified by the RSPB warden.

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Flavoured wax blocks ready for deployment as part of biosecurity on Mousa Photo: Afra Skene

Thousands of visitors’ flock to Mousa each summer to see both the wildlife and the broch, travelling to the island via commercial ferry, tour company and private vessels from the nearby Shetland Mainland and by expedition cruise ships. Biosecurity for LIFE staff are working with the RSPB to create an interpretive trail for Mousa highlighting both the island’s special wildlife and the importance for biosecurity precautions. We hope to have this up and running by June 2020, watch this space!

For more information on Mousa and how to responsibly visit check out the follow websites:

RSPB Mousa:

The Mousa Broch:

The Mousa Boat:



October 2020

St Agnes and Gugh, Isles of Scilly

The Isles of Scilly are home to our Biosecurity Officer, Northern Ireland, Wales and SW England (Jaclyn Pearson). The inhabited islands of St Agnes and Gugh in particular are very special for seabirds. Here, brown rats were removed in 2013 to protect species including Manx shearwaters and storm petrels and the results have been incredible, not just for wildlife but for the community too. Together the 85 residents of St Agnes and Gugh continue to carry out rodent biosecurity with the support of RSPB and Isles of Scilly Wildlife Trust.

April 2020

Skokholm, Skomer and Middleholm

Together these islands are estimated to hold a remarkable 67% of the world population of breeding Manx shearwater. These birds are diurnal but will only come ashore or go out to sea under the cover of darkness and nest underground so you’re unlikely to see them when you visit the islands unless you stay overnight. You will see that the ground is covered in burrows and is therefore extremely fragile so take care to stay on the paths when you visit. Skokholm is also home to the fourth largest storm petrel colony in the UK, holding 8% of the UK breeding population. These birds’ nest in crevices in stone walls or quarries and are also nocturnal when on land to avoid predation. The islands most famous resident however is the puffin, these birds nest underground but come out in the day so you are likely to see rather a lot of them if you visit between April and July. All these ground-nesting species are particularly susceptible to invasive non-native mammalian predators, they would not survive if rats, mink or stoats arrived on the islands.

March 2020


Grassholm is one of those islands that assaults your senses upon approach with both the smell, noise and sight of over 36,000 pairs of gannets. On a round island boat trip you’ll see them on their nests or flying overhead like aeroplanes before folding their wings back and diving at speed to catch their prey in the surrounding waters. 6.8% of the world population of Northern gannets breed on this lump of rock just 10 hectares in size. In fact, the majority of the island is now white in colour due to the animals and their guano, with only a relatively small strip of grass remaining where they are yet to colonise. Grassholm is the third largest gannetry in the UK after the Bass Rock and St Kilda – two other sites we’re also working on.

Illustration of birds

Contact Us

If you’d like more information or would like to report a sighting of an invasive predator please contact us using the form below: