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Vanessa Amaral-Rogers

Today’s blog is by Christopher Jones, Senior Field Assistant living on Gough Island and unravelling the mysteries of an intrepid bird.

Despite the current global travel restrictions, a young Southern Giant Petrel was spotted by fishermen near the French Overseas Territory of Amsterdam Island in the southern Indian Ocean in April.

After some investigation work, the bird was discovered to have been ringed as a chick on Gough Island in the South Atlantic in January. In a straight line, this is more than 7000 km away from Gough Island, an impressive feat for a bird that only learnt how to fly about 3 months earlier!

A photo of the fledgling southern giant petrel discovered in the Indian ocean (c) TAAF

Unravelling the mystery

The team from the fishery observation programme in the French Southern and Antarctic Lands (TAAF) overseas territory got in touch with us not long after lockdown started. They'd had news from a fisherman on board the "Austral", a lobster fishing boat operating in Saint-Paul and Amsterdam Island waters. He sent photos of a young southern giant petrel equipped with a metal ring. Fortuitously he was able to read the ring as 170 (X) 357 with an unconfirmed digit X.

Even with the missing digit, the ring closely matched a ring number (1705357) in our database from a series we had used on southern giant petrel chicks earlier this year. Given the fresh look of the plumage in the photos taken by the fisherman, the bird was likely to be a recent fledgling.

However, given the ambiguity of the unknown digit we had to rule out other possibilities. The only other colony where southern giant petrels are tagged with rings from the British Trust of Ornithology is by researchers of the British Antarctic Survey at South Georgia. The unknown digit could have been replaced with a number that hypothetically fitted with a ring series from South Georgia.

The fishermen were able to take a photo of his ring ID (c) TAAF

However, this was unlikely the case. The latitude of the colonies determines when things occur, and the colony at Gough breed and fledge the earliest since it is the northernmost site for the species. The birds on Gough are the first to fledge each season in the Southern Ocean and the South Georgian birds would have only just started fledging – not enough time to head all the way to the Indian Ocean!

Therefore, the bird could only have come from Gough. Very exciting especially as we don’t get many bird rings reported from fishing vessels – and even more rarely from live birds, since most are from dead birds that get caught on hooks and drown.

Seabird Monitoring on Gough Island

As part of the Gough Island Restoration Programme we monitor a variety of important seabird species. For the surface nesting seabirds, we ring the chicks just before they fledge from Gough (including the petrels). These birds nest in fairly dense colonies at only a few sites on Gough, and we count all nests at the peak of their egg-laying period in September.

We then monitor a subset of about 160 nests at a site on the west coast below a peak called Low Hump, approximately 8 km from the main research base and around 2 km from our remote field camp at Gonydale. Normally these ringed fledglings would only be re-sighted several years later as they return to Gough to find a partner and begin breeding themselves. So it is always a treat to hear about sightings of them at sea and we hope to see the bird that was spotted near Amsterdam Island return to Gough one day.

An adult on Gough with its chick (c) Christopher Jones

This ring and re-sight information is very valuable in monitoring the seabirds of Gough – it helps us get an idea of how many chicks survive to return to breed, how old they are when they first start breeding, how many chicks they can produce in their life and how long they live.

All this information can help us determine whether a population is doing well or poorly, and if they are not doing well we can possibly determine where the issue is and devise interventions. Interventions such as the Gough Island Restoration Programme which plans to rid the island of invasive mice which are attacking and killing millions of seabird chicks each year.

Southern giant petrel facts:

  • Although similar in size and appearance to the northern giant petrels, the two are distinct species. They can be differentiated by the colour of their bill tip (known as an unguis), southern have a greenish unguis while northerns are reddish. They are known to hybridize on islands.
  • Southern giant petrels are in the same family as prions and other petrels but compare
  • They live around the South Pole and Gough is their northernmost breeding site. Many people comment on photos on how unusual it looks to see nesting birds surrounded by trees and ferns. Most colonies are found much further south with very little to no vegetation surrounding their nests, just snow and rocks.
  • Chicks use projectile vomiting of volatile stomach oils as a defence mechanism against predators such as skuas.

The ability to vomit up their stomach contents led to sailors naming southern giant petrels ‘stinkpots’

  • Amsterdam Island is often considered the Indian Ocean equivalent of Gough, supporting some of the same or closely related plants and animals. It is interesting that this fledgling turned up there.
  • Some individuals have an almost completely white plumage. This phenomenon is generally more common the further south the breeding colony. This morph has been seen occasionally offshore at Gough but never recorded breeding.

Acknowledgement

The Gough Island Restoration Programme is being carried out by the RSPB in partnership with Tristan da Cunha, BirdLife South Africa and the Department of Environmental Affairs in South Africa, and Island Conservation. The programme is part-funded by the RSPB, the UK Government, the National Fish and Wildlife Foundation and other generous individuals and organisations.

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