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A ground-based baiting operation to eradicate introduced Norway Rats Rattus norvegicus on 123-ha Sea Lion Island (51° 55.60'S, 58° 43.80'W) in the Choiseul Sound area, Falkland Islands (Islas Malvinas)* on 23 October this year has led to the discovery by Sally Poncet of a previously unknown breeding locality for ACAP-listed Southern Giant Petrels Macronectes giganteus in the South Atlantic.

A breeding site of Southern Giant Petrels on Sea Lion Island
Photograph by Sally Poncet

The birds were found breeding in two separate colonies about 750 m apart.  Fifteen birds were present at one of the sites on 22 October when nine empty nest scrapes were counted.  The next day two of these nests contained eggs and three of five occupied nests at the second locality also had eggs, suggesting at least 14 breeding pairs for the island.  A total of 30 giant petrels was counted ashore.

It is possible, but remains unproven, that these birds had moved from Big Samuel Island, three kilometres away, where breeding by Southern Giant Petrels has been previously suspected by the discovery of empty nests in May 2011, suggesting breeding had occurred there over the previous summer (click here).

This year Big Samuel does not appear to be supporting a giant petrel colony based on a check made on 15 October; lending credence to the idea of relocation having occurred.

The Southern Giant Petrel breeding population of the Falkland Islands (Islas Malvinas)* in 2004/05 was estimated to be approximately 19 529 pairs (range 18 420 - 20 377) breeding in 38 localities around the islands, with colony size varying from one to 10 936.

Southen Giant Petrel guarding its chick
Photograph by John Cooper

Reference:

*Reid, T.A. & Huin, N. 2008.  Census of the Southern Giant Petrel population of the Falkland Islands.  Bird Conservation International 18: 118-128.

Also see http://www.falklandsconservation.com/wildlife/birds/GiantPetrelReport.pdf.

With thanks to Sally Poncet for information.

John Cooper, ACAP Information Officer, 12 November 2011

*A dispute exists between the Governments of Argentina and the United Kingdom of Great Britain and Northern Ireland concerning sovereignty over the Falkland Islands (Islas Malvinas), South Georgia and the South Sandwich Islands (Islas Georgias del Sur y Islas Sandwich del Sur) and the surrounding maritime areas.