Seabirds in the Isles of Scilly ~ Why is Scilly important?

The Isles of Scilly support an internationally important seabird assemblage both in terms of numbers and diversity. The last full survey of all seabirds across the islands in 2015/16 confirmed it as the most significant seabird colony in southwest England

  • Over 8,000 pairs of 13 species of breeding seabird supported: Manx shearwater, fulmar, storm petrel, shag, cormorant, great black-backed gull, lesser black-backed gull, herring gull, kittiwake, common tern, puffin, razorbill and guillemot
  • Breeding seabirds distributed across 50+ sites throughout the archipelago
  • Internationally important numbers of lesser black-backed gull and storm petrel
  • Nationally important numbers of great black-baked gull and shag
  • Regionally important numbers of puffin, razorbill, Manx shearwater, fulmar and common tern
  • One of only two sites in England where Manx Shearwater and storm petrel breed (the other is Lundy).

Protections & Designations in place: 

  • Area of Outstanding Natural Beauty (AONB) – The Isles of Scilly are designated as an AONB to safeguard, enhance and promote the distinctive landscapes, wildlife, historical and architectural character of the Islands', whilst fostering the social and economic well-being of its people.
  • RAMSAR – Scilly is designated a RAMSAR wetland of international importance due to its breeding populations of storm petrel and lesser black-backed gull as well as shags.
  • Special Protection Area (SPA) – A large part of the islands are designated an SPA for the breeding seabird assemblage with nesting populations of storm petrel and lesser black-backed gull of European importance. Currently the SPA boundary only encompasses those areas used for nesting; Natural England are working towards extending the seaward boundaries to encompass the marine feeding areas used by the seabirds as well.
  • Sites of Special Scientific Interest (SSSI) – there are 26 SSSIs in Scilly; 17 of these support breeding seabirds with 7 of these noted in whole or part recognition of their qualifying seabird interest.
  • Important Bird Area (IBA) – Scilly is recognised as an IBA for its populations of storm petrel, European shag, ruddy turnstone (non-breeding), common tern, lesser and greater black-backed gull.
  • Special Area of Conservation (SAC) – The whole archipelago is designated an SAC under the EC Habitats Directive. Although designated in particular for grey seals and shore dock, this designation encompasses the important marine habitats, including sandbanks, mudflats and reefs, surrounding the islands in addition to the islands themselves.
  • Marine Conservation Zones (MCZ) – In 2013 as part of the first tranche of marine designations 11 separate sites covering a total area of over 30 km2 around the islands were designated MCZs. 10 of the 11 sites lie within the SAC and complement this existing designation by offering protection to species and habitats that are not protected by the SAC.
  • WiSE Operating - In addition to all of these designations the Wildlife Trust have formed a Marine Protected Area working group of local marine operators on Scilly and organised WiSe (Wildlife Safe) training to encourage marine users to operate at a safe distance from seabirds and other marine life.
  • Closed Areas – As a result of these designation and in order to give our sea and coastal birds the best chance of rearing young, a number of uninhabited islands are closed year round and others, both inhabited and uninhabited, have areas of restricted access during the breeding season. These restrictions are shown here.

Seabird population trends in Scilly

We have a great set of data on seabird numbers in Scilly with regular all-island counts completed since 1970. In April 2018 the Trust employed a Seabird Ecologist to continue this programme of important ongoing seabird research. A number of reports document the survey findings in more detail, but these are some of the main points;


  • The overall number of breeding seabird pairs declined by 31.4% between 1983 and 2015/16
  • Annual counts of Annet breeding numbers have fallen by 29% since 2000 (mainly a reduction in herring and lesser black-backed gull numbers)
  • Common tern – steep decline in numbers, with total breeding failure in 5 of the last 8 years; could soon be lost as a breeding species
  • Kittiwake – 89% drop in numbers and loss of 5 sub-colonies since 2006, with total breeding failure in 6 of the last 12 years; major driver of this appears to be reduced food availability
  • Herring gull, Lesser black backed gull and Shag breeding populations have all declined by over 20% since 2006
  • Manx shearwaters – numbers trebled from 171 pairs in 2006 to 523 pairs in 2015; this is likely due to recruitment from nearby shearwater populations on Lundy and further afield in Wales following the removal of rats
  • The successful removal of rats from St Agnes and Gugh in 2013 has resulted in the first successful breeding of Manx shearwaters there in living memory, as well as the first confirmed breeding by storm petrels in 2015
  • Since 2006 there has been a marked increase in the numbers of both razorbill and guillemots across the islands, whilst puffins have remained relatively stable.

 Threats facing our seabirds

The survival of our seabirds is threatened by the pollution, overexploitation and degradation of our marine and coastal habitats. 

A number of factors are likely to influence overall seabird breeding numbers and success with threats sometimes acting in combination so that whilst some factors may be having an impact on breeding seabirds they may not be the primary cause but just a symptom of a wider problem. At sea, issues include changes in food sources, bycatch and pollution. On land, the biggest threat to seabirds is the predation by non-native invasive animals of the eggs, young and adults. Other factors include disturbance, persecution and other forms of predation. Climate change could have a significant effect on some species, particularly those at the edge of their range.

In Scilly the biggest threat to those seabirds that nest in burrows such as Manx shearwaters and storm petrel is predation by rats. The Trust worked in partnership with the Seabird Recovery Project from 2012-2017 to remove this threat from the birds which breed on St Agnes and Gugh. This has resulted in an impressive increase in birds and successful breeding of both shearwaters and petrels there.

The Trust is now managing the Legacy Phase of this partnership project to ensure that the islands remain rat-free. For other species such as Kittiwake and the larger Gull species, productivity studies indicate that the underlying issue is changes to the availability of food at sea which is likely related to climate change. Food is also probably an underlying issue for common tern but this is masked by the effects of high tides and storm events inundating nests on their preferred breeding island. Disturbance may also be an issue at some sub-colonies around the coasts of the larger more visited islands, whilst the ingestion of marine plastics affects many seabirds particularly fulmar, Manx shearwater and Herring gulls. 

Read more about the Trusts ongoing seabird research and work to protect seabirds here.