Rodent control on the Scilly Isles

Rats Ahoy!

In the summer of 1707, during the war of the Spanish Succession, a fleet of 21 ships left Gibraltar heading for England. Due to bad weather and a navigational error the fleet went off-course, struck rocks near the Isles of Scilly and four ships were lost along with the lives of some 1,400 to 2,000 seamen. It was one of the greatest maritime disasters in British history. For days afterwards bodies and wreckage were washed on to the isles and many sailors were buried on the island of St Agnes.


In the past brown rats (Rattus norvegicus), were frequent inhabitants on ships and are known to be able to swim for about half a mile in open sea and tread water for up to 3 days. It is likely that it was during these renowned shipwrecks that brown rats first set paw on St Agnes.

Situated 28 miles off the south-western tip of the Cornish coast, the Isles of Scilly are designated an Area of Outstanding Natural Beauty and are highly protected for their breeding seabirds, forming part of the ‘Natura 2000’ network of globally important conservation sites. The Isles comprise an archipelago of five inhabited islands and many small rocky islets. St Agnes, and neighbouring Gugh, (which are linked by a sandbar) is the fourth smallest island with a population of 82 island residents.


Recent concerns from RSPB, Natural England, Isles of Scilly Wildlife Trust and other local conservation groups about the declining seabird numbers on St Agnes were well founded following a full breeding survey. This revealed that 20,000 breeding birds of 14 species had declined by a quarter between 1983 and 2006. The Isles of Scilly are unique in having England’s only known colony of storm petrels (1,398 pairs) as well as 171 pairs of Manx shearwaters.


What was the cause of this decline? A study undertaken on Lundy Island, showed that non-native brown rats are the greatest threat to these two special birds, as they predate on the eggs, chicks and adults. With a known population of brown rats on St Agnes and Gugh it was clear that they were having an impact, and were a key factor in declining seabird numbers. By removing the rats seabird numbers should eventually recover, and could also benefit the declining population of lesser white-toothed (‘Scilly’) shrew, found nowhere else in Britain.


“The project we want to undertake on St Agnes and Gugh mirrors what took place on Lundy in 2004 and resulted in a strong recovery of the seabird breeding population there,” said Jaclyn Pearson, Isles of Scilly Seabird Recovery Project Manager. “If we are successful, it will be the largest inhabited i

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