Over the last five years or so, I led an investigation into the taxonomic standing of 'São Tomé Storm Petrel' – an undescribed local form of Band-rumped Storm Petrel – the findings of which are soon to be published. São Tomé is an island in the Gulf of Guinea in the equatorial eastern North Atlantic Ocean. In June 2023, as part of a 10-day study program, we ran four short-range pelagic trips off São Tomé and used chum to draw in the storm petrels for observation and photography. Plenty of Band-rumped Storm Petrels arrived along with 10 Wilson's Storm Petrels.
Careful scrutiny of the photographs revealed quite a surprise – but this came from the Wilson's Storm Petrels, rather than the São Tomé Storm Petrels! Photographs taken by my co-researcher, Kirk Zufelt, showed that all of the Wilson's exhibited characteristics of the subspecies chilensis, known as 'Fuegian Storm Petrel', which breeds in southern to central Chile and possibly the Falkland Islands. It has been suggested that this form may occur off south-western Africa. Over the years we have made extensive studies of Fuegian Storm Petrel off Chile. Further genetic work on this form is underway in the Pacific in order to establish its exact taxonomic status.
Known Fuegian Storm Petrel photographed in the Humboldt Current off Chile (Kirk Zufelt).
It is a simple matter of logic that presumed Fuegian Storm Petrels must therefore occur not only off São Tomé but elsewhere in the Atlantic. The Cornell Lab of Ornithology's Macaulay Library has a wealth of publicly accessible media including photographs contributed by the public from around the world. The library holds approximately 10,000 photographs of Wilson's Storm Petrels taken in the Atlantic. I looked through them all and found that birds showing characteristics of Fuegian Storm Petrel regularly occur northwards to the equatorial regions on both sides of the South Atlantic, but they are rarely sighted in the temperate zone of the North Atlantic or in the Southern Ocean to the Antarctic continent. The latitudes at which the presumed Fuegian Storm Petrels regularly occur in the Atlantic mirror those of the known range of the taxon off western South America. This is quite a discovery.
The revelation became even more interesting from a Western Palearctic (WP) perspective when I recalled that, several years ago, Spanish seabirder friend, Gorka Ocio, had sent me photographs from his research trips of numerous Wilson's Storm Petrels off Liberia and Senegal showing white in the underwing coverts and in the belly feathers.
Presumed Fuegian Storm Petrel photographed off Senegal on 4 June 2016 (Gorka Ocio).
On account of this, the range of presumed Fuegian Storm Petrel on the eastern side of the Atlantic can be summarised as follows. Concentrations of presumed Fuegian Storm Petrels off South Africa and São Tomé indicate a continuity in range off the west coast of Africa, including photographs for Gabon, up the Benguela and Angola currents to the Gulf of Guinea, across the Guinea Current to Liberia, and northwards at least as far as Senegal. Fuegian Storm Petrels might occur westwards of Senegal in Cape Verde, and therefore in the WP.
Interestingly, two individuals photographed from Scilly Pelagics showed characteristics of Fuegian Storm Petrel and I documented these in 2011 in British Birds (104: 272–273). The birds may represent rare variation in Wilson's Storm Petrel, but equally may have been stray Fuegian Storm Petrels.
All that said, we do not exclude an unknown taxon as an explanation for the presumed Fuegian Storm Petrels in the Atlantic, although we have found no evidence to support that idea.
Wilson's Storm Petrel photographed at sea off the Isles of Scilly. This bird shows some white in the underwing, suggestive of Fuegian Storm Petrel (Brent Stephenson).
Wilson's Storm Petrel observed in the Gulf Stream off Hatteras, North Carolina, USA, 22 May 2023. The least marked Fuegian Storm Petrels look virtually identical to a typical Wilson's Storm Petrel (Kirk Zufelt).
Reference
Flood, R L, de Lima, R F, Melo, M, and Zufelt, K. 2024. Presumed Fuegian Storm-Petrels Oceanites oceanicus chilensis off São Tomé, Gulf of Guinea, and in the North and South Atlantic Oceans. Marine Ornithology 52. First published online.
