Northern Giant Petrels Macronectes halli are one of the earliest breeding species on Bird Island, South Georgia (Islas Georgias del Sur)* with first eggs laid between 13 and 18 September 2014 in a study area which contains approximately 300 nests.  Around 60 pairs of Brown or Subantarctic Skuas Catharacta antarctica also nest in the area, being absent for the coldest months of winter, and returning in early to mid-September.  At this time the ground is often frozen and snow-covered; Gentoo Pygoscelis papua and Macaroni Eudyptes chrysolophus Penguins have yet to lay and Antarctic Fur Seals Arctocephalus gazella have not yet given birth, so there is very little terrestrial food available for skuas.

 Northern Giant Petrel, photograph by Marienne de Villiers

In recent years skuas have been seen harassing giant petrels and this spring two instances of egg theft have been caught on camera.

In the first video clip (from 23 September 2014) a pair of skuas is seen working together.  The first skua drops in behind a male giant petrel sitting tight on its egg, and tugs at its tail feathers before calling to the second bird.  As the second skua appears in front of the petrel the first skua resumes tugging on the tail. In an effort to reach its assailant the petrel stands and twists a little, giving just enough time for the second skua to snatch the egg out from under it and fly away.

The second clip (from 24 September 2014) shows a single skua jumping from side to side, tugging at a female giant petrel’s tail and wings, encouraging it to stand and climb off the nest.  This is complicated by the presence of a second giant petrel (not the partner of the incubating bird), but when he leaves the skua is able to steal the egg after dragging her away by her outstretched wing.

Although failure during incubation is not uncommon in giant petrels and albatrosses breeding on Bird Island, until this footage was recorded it was generally assumed that egg predation by skuas only occurred after the incubating adult had deserted the nest and left its egg unattended.  Despite thousands of visits to colonies over the years, active egg theft by skuas has never been seen before, which suggests it was, and perhaps still is, an unusual behaviour.  An adult giant petrel is a formidable predator, twice the mass of a Brown Skua, so trying to steal its egg carries an element of risk.  It is unknown whether this egg-stealing behaviour is a new feeding method, or, given the skill required, has always been used but only by a small number of specialised individuals.

With thanks to Andy Wood for assistance.

Jerry Gilham, British Antarctic Survey, Cambridge, UK, 15 October 2014

*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.

It is now well known that the Critically Endangered Tristan Albatross Diomedea dabbenena is under serious threat from attacks on its chicks by “killer” House Mice Mus musculus on the United Kingdom’s Gough Island, its major breeding site (at most one to two pairs breed annually on Inaccessible Island in the Tristan Group).

A Tristan Albatross chick shows signs of wounds inflicted by mice in 2013, photograph by Peter Ryan

During annual relief voyages to Gough Island each spring, a high priority is to count the Tristan Albatross chicks across the entire island to assess the year’s breeding success.  The results from this year’s expedition, which returned to South Africa last week, are dire with only 9.8% of the eggs laid in January resulting in live chicks surviving to September.

According to Peter Ryan, Director of the University of Cape Town’s FitzPatrick Institute and Expedition Leader “the albatross chick count of 163 in 2014 was the lowest total ever, giving an island-wide breeding success of below 10% for the first time.  Annual chick production has fallen by more than 80% since the first island-wide count 15 years ago, confirming the serious impact mice are having on this species.  As usual, the north of the island was particularly hard hit, but we weren’t prepared for the magnitude of the impact there.  In the lower-lying areas of West Point and GP Valley only two chicks survived out of more than 400 breeding attempts.”

The 2014 counting party gets dropped by helicopter in GP Valley - with not a single Tristan Albatross chick in view

Photograph by Peter Ryan

Great albatrosses of the genus Diomedea should successfully raise chicks from 60-70% of breeding attempts, based on studies on islands where chicks are not attacked by rodents, six to seven times higher than the situation on Gough this year.

The Royal Society for the Protection of Birds (RSPB) has been studying the feasibility of eradicating Gough’s mice by using helicopters to drop poison bait over the entire island (click here).

At its recent meeting in Uruguay the ACAP Advisory Committee agreed that the removal of introduced House Mice from Gough Island was a particularly high priority to help conserve the Tristan Albatross, as well as other ACAP-listed seabirds that breed on the island (click here).

Research on threatened birds on Gough Island is undertaken jointly by the FitzPatrick Institute and the RSPB with support from the Tristan Conservation Department and the South African Department of Environmental Affairs.

With thanks to Peter Ryan for information ansd photographs

John Cooper, ACAP Information Officer, 14 October 2014

A total of 251 incubating pairs of ACAP-listed Southern Giant Petrels Macronectes giganteus was counted at four different localities on the United Kingdom’s Gough Island in the South Atlantic last month by Peter Ryan and colleagues of the University of Cape Town's FitzPatrick Institute.  Gough is the most northerly breeding locality for the species.

One of two pairs of Southern Giant Petrels incubating on Long Beach on Gough's east coast in September 2014, photograph by Peter Ryan

The two previous complete-island counts were of 253 incubating pairs in 2012 and 223 in 2013.

Compared to the previous counts, the numbers of breeding birds in Giant Petrel (“GP”) Valley were up, while the numbers in the demographic study colony below Low Hump were down.  However, there is no evidence that colour-banded birds from the Low Hump colony move to other breeding sites on the island, so the year-to-year fluctuations may reflect local variations in the numbers of birds missing a breeding year by taking so-called “sabbaticals”.

Unlike for a number of other seabird species on Gough, there are no observations of giant petrel chicks being attacked by introduced House Mice Mus musculus, which might help explain their currently stable population on the island.

Avian research on Gough Island is conducted with the approval of the Tristan Conservation Department and is supported logistically by the South African Department of Environmental Affairs.

With thanks to Peter Ryan for information and the photograph.

Selected Literature:

Cuthbert, R.L., Ryan, P.G. & Cooper, J. 2013.  Population trends and breeding success of albatrosses and giant petrels at Gough Island in the face of at-sea and on-land threats.  Antarctic Science 26: 163-171.

John Cooper, ACAP Information Officer, 13 October 2014

Christophe Barbraud (Centre d'Etudes Biologiques de Chizé, Villiers-en-Bois, France) and colleagues have published in the open-access journal Marine Ornithology on survivorship in Flesh-footed Shearwaters Puffinus carneipes in New Zealand.  The species, identified as a potential candidate for ACAP listing (click here), is currently categorized globally as of Least Concern.  However, the authors argue that its conservation status should be reassessed “urgently”.

The paper’s abstract follows:

The Flesh-footed Shearwater Puffinus carneipes is a widespread sub-tropical species, breeding on Southern Hemisphere islands managed by New Zealand, Australia and France.  Recent concern over the population’s stability and frequently noted bycatch in longline fisheries has prompted a review of its conservation status.   Studies of nesting shearwaters at two sites presented here provide detail of survivorship rates for two populations, studied over 13 and 23 years, respectively, in northern New Zealand sites.  Adult survival (0.93–0.94) is moderate to high compared with survival of congeners.  Population growth rates estimated from marked individuals indicate stability for one site and decline at the other site.  Average age of first return of banded chicks was 6.2 years of age in one study and 6.4 years in the other. Current threats affecting survivorship for the New Zealand populations of this species are reviewed.”

Flesh-footed Shearwater, photograph by Tim Reid

Click here to access a recently published paper on the conservation status of the Flesh-footed Shearwater in Australia.

Reference:

Barbraud, C., Booth, A., Taylor, G.A. & Waugh, S.M. 2014.  Survivorship in Flesh-footed Shearwater Puffinus carneipes at two sites in northern New Zealand.  Marine Ornithology 42: 91-97.

John Cooper, ACAP Information Officer, 12 October 2014