Evidence of breeding White-faced Storm-petrel Pelagodroma marina on St Helena Island, South Atlantic: vagrancy or a relict from human pre- colonisation?
Bolton, M.1* 
, Watt, R.2, Ellick, G.,3 and Scofield, P.4
https://doi.org/10.61350/sbj.23.135
* Correspondence author. Email: Mark.Bolton@rspb.org.uk
1 RSPB, UK Headquarters, The Lodge, Sandy, Beds. SG19 2DL, UK
2 12 Dalmore Crescent, Helensburgh, Argyll and Bute G84 8JP, UK
3 St Helena National Trust, PO Box 113, Broadway House, Island of St Helena, South Atlantic Ocean, STHL 1ZZ
4 Canterbury Museum, Rolleston Ave, Christchurch 8013, New Zealand
Abstract
During an overnight ringing expedition to the Oceanodroma storm-petrel colony on Egg Island, St Helena in July 2009, a White-faced Storm-petrel Pelagodroma marina was found on the ground under an open mist net. The bird was easily captured and close examination in the hand, together with subsequent inspection of photographs, showed that the bird was recently fledged. Biometrics and timing of fledging preclude provenance from the closest colony on the Tristan da Cunha archipelago and the pristine nature of the plumage render an origin from the northerly colonies of Cape Verde or the Selvagens Islands, around 4,000 km distant, unlikely. We suggest this bird probably fledged locally, quite possibly on Egg Island itself, where the substratum is suitable for burrowing. The length of the bird’s tarsus was within the range of sub-fossil specimens from St Helena, which show the species was once widespread and abundant there. This recently-fledged individual raises the possibility that a relict population may persist on one or more of the predator-free offshore stacks that surround the St Helena mainland.
Introduction
The island of St Helena, including its 24 satellite islets and stacks, provides the closest nesting location for seabirds within an area of 3,625,000 km2 in the South Atlantic Ocean, and yet it supports only modest numbers of relatively few species (Rowlands et al. 2008). Abundant sub-fossil remains reveal that the island formerly supported a more diverse seabird assemblage, including three endemic species, two of which likely became extinct due to the introduction of mammalian predators following the discovery of the island in 1502. The White-faced Storm-petrel is known from sub-fossil remains to have occurred on St Helena and the availability of light, sandy soils in which it nests, and the abundance and distribution of sub-fossil remains indicate that it bred in considerable numbers (Olson 1975). There are no published records of any occurrence of White-faced Storm-petrel on St Helena since the island was settled and due to the species’ extreme vulnerability to ground predators it is likely to have been rapidly extirpated from the mainland. There have been several records of the species at sea, some between 308 and 424 nautical miles (570–785 km) to the northwest of St Helena in late January and early February (Rowlands 1992), and these were presumed to be birds from the nearest known breeding colony on the Tristan da Cunha archipelago (Richardson 1984), some 2,400 km distant. Here we report the first occurrence of a White-faced Storm-petrel on St Helena, a recent-fledgling found at night within a breeding colony of Oceanodroma storm-petrels, on a tiny offshore islet, Egg Island. We discuss the origins of this individual and the prospects for the existence of a relict breeding population on St Helena.
Acknowledgements
We thank the St Helena Government for permission to work on Egg Island, and Jonnie Herne for providing excellent boatmanship in landing us on the island under difficult conditions. Andrew Darlow provided logistic support and much encouragement for our work on St Helena. RW was supported by an award from Chester Zoo.
References
Homing in Leach’s Petrel. The Auk 85: 36–43. [Crossref]
Northward migration of European Storm-petrels Hydrobates pelagicus captured in Portuguese coastal waters. In: Beja, P., Catry, P. and Moreira, F. (eds.) Actas do II Congresso de Ornithologia da Sociedade Portuguesa para o Estudo das Aves: 34–35. SPEA, Lisboa.
Moult and ageing of British Storm-petrels Hydrobates pelagicus. Ringing and Migration 20: 193–201. [Crossref]
On the Races of the Frigate Petrel, Pelagodroma marina (Latham) with a New Race from the Cape Verde Islands. Bulletin of the British Ornithologists’ Club 73: 79–82.
Breeding biology of the White-faced Storm-petrel on Selvagem Grande Island, north-east Atlantic. Waterbirds 22: 199–206. [Crossref]
The Birds of the Western Palearctic. Vol. I. Oxford University Press, Oxford.
Roberts Birds of Southern Africa. 7th edition. Trustees of the John Voelcker Bird Book Fund, Cape Town.
A Review of the Frigate-petrels (Pelagodroma). American Museum Novitates 1506: 1–17.
Paleornithology of St Helena Island, South Atlantic Ocean. Smithsonian Contributions to Paleobiology 23: 1–49. [Crossref]
Aspects of the ornithology of the Tristan de Cunha group and Gough Island 1972-1974. Cormorant 12: 123–201.
Petrels night and day. The Sound Approach, Poole.
Seabird observations between Ascension, St Helena and Tristan de Cunha in the central South Atlantic. Marine Ornithology 20: 25–42.
The Birds of St Helena. An annotated Checklist. British Ornithologists’ Union, Tring.
Field guide to the animals and plants of Tristan da Cunha and Gough Island. Pisces Publications, Newbury.