Why is Scilly important?

Scilly is regionally, nationally and internationally important for breeding seabirds both in terms of number of birds and diversity of species.  Having:

  • 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-backed gull and Shag;
  • Regionally important numbers of Puffin, Razorbill, Manx shearwater, Fulmar and Common tern;
  • and being one of only two sites in England where Manx Shearwater and Storm petrel are currently known to breed (the other is Lundy).

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 (Vickie) 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 shearwater – 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 from St Agnes & Gugh;
  • 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, over-exploitation 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; just a symptom of a wider problem.

At sea, issues include changes in food sources, by-catch 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 of St Agnes & Gugh 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. 

What are we doing about it at the Trust and how can you help?

Birds are widely accepted as excellent indicators of environmental health; their changing populations often providing clues to the overall health of their habitat. Sadly we have recorded alarming declines in many of our seabird populations over recent years, showing that there is a clear need to take action. The information that the Trust gathers on our seabirds not only contributes to long-term data sets, but also informs our Habitat Management Plans and wider marine protection work in future.

As part of the Trusts wider marine campaign there are a lot of marine themed walks and events helping to raise awareness of the issues affecting our seabirds as well as weekly Wildlife Safaris to join. The Trust have also formed a Marine Protected Area working group of local marine operators in Scilly and organised WiSe (Wildlife Safe) training to encourage marine users to operate at a safe distance from seabirds and other marine life.

The Ranger Team continue to carry out programmes of winter land management work, much of which is for the benefit of breeding seabirds.

And not forgetting Plastic Free Scilly, a community initiative, co-ordinated by the Trust, to reduce the use of single-use plastics in Scilly, which benefits our seabirds by reducing the amount of plastic debris available for them to ingest.