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From the Rarities Committee’s files: Rare seabirds and a record of Herald Petrel Ian Lewington ABSTRACT Rare seabirds are often extremely hard to identify, and a significant part of the problem is that, when observed from land, circumstances are typically very difficult. In many cases, one or more of the following drawbacks applies: the weather conditions are poor, views are distant and brief, and photographic evidence is impossible. For these same reasons, records of rare seabirds are also difficult to assess, particularly so if they concern what would be a ‘first for Britain’ for the species in question.This was the case when a probable Herald Petrel Pterodroma arminjoniana was seen off Dungeness, Kent, in January 1998. In this paper, the circumstances and the assessment of that record are described, and, more generally, the level of supporting evidence which is necessary for acceptance of records of rare seabirds is discussed. 156 © British Birds 95 • April 2002 • 156-165 Rare seabirds and a record of Herald Petrel are seabirds present difficulties in many panic was beginning to set in. Had we missed ways. They are difficult to find, and most it? A few seconds later, the mystery seabird Robservers will spend hundreds of hours came into our field of view, trailing behind a ‘sifting through’ common species before Northern Gannet Morus bassanus and flying encountering a rarity. They are difficult to iden- steadily west, low over the water, about 400 m tify, not least because the circumstances in offshore. which they are seen usually mean that, com- At the time of the observation the light was pared with most other birding situations, views dull but clear, in fact excellent for observing are both distant and brief, and the observer is colour tones. The presence of the nearby rarely given a second chance to confirm the fea- Northern Gannet allowed a good size compar- tures noted on first impressions. From a rarities ison, while several Fulmars Fulmarus glacialis committee’s point of view, they are extremely and Kittiwakes were also seen under similar difficult to assess. Rare seabirds are usually seen light conditions and range prior to the sighting. by a small number of observers, the weather My initial impression was of a shearwater, and viewing conditions are often poor, and about the size of a slim Cory’s, but with huge there are rarely any supporting photographs. In white flashes on the underwing (resembling a addition, the observers are frequently either boldly marked juvenile Pomarine Skua Sterco- unfamiliar with the species or used to seeing it rarius pomarinus), a broad breast band, a faint in a different context (for example, at close impression of an ‘M’ pattern on the upper- range, from a boat in calm conditions). wings, a few curious pale feathers in the wing- These problems are amplified both for coverts, and a peculiar narrow-winged and observers and for BBRC when the species con- long-tailed appearance, somewhat reminiscent cerned is new for Britain. This was the case of a juvenile Long-tailed Skua S. longicaudus.I when a probable Herald Petrel Pterodroma watched it for perhaps two minutes, until it was arminjoniana was seen off Dungeness, Kent, in eventually lost from view, during which time all January 1998, by David Walker, Owen Leyshon three of us called out comments and plumage and Chris Philpott. David Walker describes the features as it passed by. After it had disappeared, circumstances of the event, and the identifica- we simply sat there for a while as we collected tion process, as follows. ourselves and made mental and verbal notes of what we had seen. I mentioned at the time that On Sunday, 4th January 1998, after a prolonged it might have been a Herald Petrel, since I was period of extremely stormy weather, I decided aware that that species had been claimed in the to check the sea at Dungeness for any signs of past, although never formally submitted. The movements of displaced seabirds. I arrived at following description was compiled from our the Coastguards Tower at 09.40 hours and field notes. decided to watch from my car, since the weather was still very unpleasant. Chris Size and shape Philpott was already there in his vehicle, and I I estimated the bird to be slightly smaller than a was soon joined by Owen Leyshon. It was still Cory’s Shearwater, perhaps nearer to an Arctic Skua S. parasiticus in general dimensions, but with a com- very windy, with frequent spells of driving rain, pletely different shape. The wings were much nar- but the light was good in the intervening rower than those of a Cory’s, while the tail appeared periods and it was evident that good numbers relatively long, similar in shape to that of a juvenile of Kittiwakes Rissa tridactyla and, more unusu- Long-tailed Skua. Although the wings were narrow ally, a few Great Skuas Catharacta skua were and the tail long, it was still quite bulky. moving out of the North Sea in a westerly direction. At about 09.55, CP called out that a Plumage large shearwater was approaching. Owing to The upperparts were ‘milk-chocolate’ brown, with the the way in which OL and I were aligned in the wing-coverts slightly darker than the mantle, and car, I was unable to see it and waited impa- with a faint scaly appearance. Within the wing- coverts, there were a few white feathers. The flight tiently for it to come into view. The next call feathers were slightly paler brown than the coverts. from CP then came… ‘It’s not a Great [Puffinus This subtle difference in colour gave rise to a faint ‘M’ gravis] or a Cory’s Shearwater [Calonectris across the upperparts, although at no time was this diomedea]: I don’t know what it is!’ At this feature striking. There was no sign of a white flash on point, OL and I had still not seen the bird and the upperwings. The underparts were mainly pale, a British Birds 95 • April 2002 • 156-165 157 Rare seabirds and a record of Herald Petrel brownish white, but with a broad, ill-defined, brown tion, one photograph showed a long-tailed band across the upper breast, of the same colour as appearance; the flight action was described as the upperparts. The belly and throat were pale, while gliding, not soaring and arcing; there was no the rest of the head appeared to be brown. The upper- sign of a white leading edge to the wing in any tail, the vent and the undertail were also brown, like of the photographs; there was little indication the upperparts. The underwings were the most of an ‘M’ on the upperparts, although the striking part of the bird. There was a large white area at the base of the primaries, and a white band across coverts appeared darker than the flight feathers; the base of the primary coverts, divided by a dark and the upperparts showed a number of iso- line, as on a Pomarine Skua. The inner white band lated white feathers. extended as a broad white line through the centre of I contacted Anthony McGeehan, who kindly the wing, probably along the base of the underwing- sent slides of a Herald Petrel which he had seen coverts. The rest of the wing was dark, with no hint of off North Carolina, USA, together with copies white on the leading edge of the underwing. of some of the references mentioned in Dubois & Seitre (1997). The slides from AM clearly Flight showed large white underwing patches, similar The petrel flew past low above the water, in a straight to those of the Dungeness petrel. The texts line, occasionally with a slight roll from side to side. The wings appeared to be slightly bowed for most of were, however, of limited value, since they the time, since it was simply gliding into the wind, but referred mainly to dark-morph individuals and at times it would give a short bout of rapid, fluttering contained little field information. Gochfeld et wing flaps, mainly from the wrist down, i.e. just the al. (1988) did, however, mention the long, wingtips seemed to be flapped. At no time did it rise wedge-shaped tail, while Lee (1984) noted the high into the air, or soar. flight as being more like that of a shearwater than that of a gadfly-petrel, and observed that We returned to the Observatory to compare our the light patches on the underwing suggested a notes with the available literature while the skua. Finally, Charles Wilkins provided me with sighting was still fresh in our minds (there two slides of pale/intermediate-morph Herald seemed little point in continuing with the sea- Petrels taken at Round Island, in the Indian watch). The only reliable material seemed to be Ocean. These seemed to remove any remaining the two books by Harrison (1983, 1987). The doubts. The coloration of the upperparts was drawings of Herald Petrel in the former (Har- exactly as on the Dungeness petrel, being pale rison 1983) were quite close to what we had brown and not at all blackish. The wings also seen, but there were some differences. The main lacked both a white leading edge and a striking points about our bird which seemed not to fit ‘M’ on the upper surface, and had occasional, were: (i) it was possibly too large; (ii) the flight isolated white feathers; in short, they were vir- action was ‘wrong’; (iii) the upperparts were tually identical to those of the seabird which we not dark enough; (iv) the wing lacked a pale had seen.

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