The descriptive text, below the map, is from the Cornish Red Data Book (2009). The map on this web page depicts the organisms distribution and shows the records made pre-2000 and those made since.
Range & Status
In Britain and Ireland a near endemic (250,000+ breeding pairs, 94% of world population); (small numbers also breed in Brittany and Channel Islands). It winters in the South Atlantic.
Cornwall: common offshore (chiefly north coast), April to September, but no longer breeds (reputed to have done so along north coast until 1930s). The southernmost substantial breeding colonies are on the Isles of Scilly. Populations are very difficult to census, but have declined. Counts in 1999 showed 201 pairs and in 2006 there were 171 pairs on six islands. The Scilly population is regionally important. Breeds on offshore islands, visiting breeding colonies under cover of darkness. Otherwise a pelagic species.
Predation by Brown Rats Rattus norvegicus is a serious threat to colonies. There is some predation by Great Black-backed Gulls Larus marinus but nocturnal attendance of Shearwaters at colonies and the decline in gull populations limit the importance of this.
Thorough census difficult but numbers need to be assessed and key sites monitored. The continuation of recent rat control programme on island in Scilly is essential. Listed (long list) as a globally threatened/declining species (BSGR, 1995).
I.J. Bennallick, S. Board, C.N. French, P.A. Gainey, C. Neil, R. Parslow, A. Spalding and P.E. Tompsett. eds. 2009. Red Data Book for Cornwall and the Isles of Scilly. 2nd Edition.Croceago Press.
The Cornish Red Data Book Project was led by the Cornwall and Isles of Scilly Federation for Biological Recorders (CISFBR). The full text and species accounts (minus the maps) are available on the CISFBR website.