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Feas / Zinos Petrel at Porthgwarra, Cornwall, on 26/8/99.
Andrew J. Musgrove
15, Long Lane, Stoke Holy Cross, Norfolk NR14 8LY.
Following a weather forecast of 15 mph south-westerly winds, I went for a morning sea-watch at Porthgwarra in the hope of seeing a few Corys Shearwaters, watching from 0740 to 1105. About 25 other observers were also present. Visibility was excellent and I was using a 20-60 zoom x 60 scope. In the event, it was an extremely good morning for Corys, with an estimated 900 passing from east to west during the time I was there (and apparently there were 1470 during the whole day). Additionally, I recorded counts of about 40 Fulmars, 40 Manx Shearwaters, one Mediterranean Shearwater, six Storm Petrels, 300 Gannets, two Common Scoters, ten Great Skuas, five Kittiwakes and two Basking Sharks. Most of the Corys were passing at approximately the distance of the Runnel Stone (1.5 km away) although some were much closer.
At about 1030, I picked up a bird quite well to the east, flying west. The bird struck me as odd immediately on its general shape and its flight action and I soon suggested other observers should look at it, which people did. I think most people got onto it when it was still quite well east of the Runnel Stone. After a little while (a minute?) I ventured the opinion that the bird might be a Feas Petrel. We continued to watch the bird until it had passed out of sight to the west, probably having had it in view for about three minutes. I then joined with several of the other observers to discuss the features noted by everyone. No-one disagreed that the bird was probably a Feas-type petrel, although we had no books present at the time. I phoned the sighting in to "Birding South West" and left at 1105 since Id run out of money for the car park. Whilst driving back to Marazion I stopped to celebrate with a bar of chocolate at ca 1130 and wrote out as full a description as I could. This was before getting to look at any books, and is repeated here (with the English improved slightly).
At ca 1030, a bird seen in partial silhouette. Not a Corys and so drew attention, given the number of Corys passing. First thoughts of Manx (since smaller than Corys and apparently black and white) and then of Arctic Skua (since it had obviously pointed wing tips). The flight action was odd, the bird shearing "too far" each side. As the angle of the light improved I soon realised that it had an all dark underwing contrasting with a white belly and alarm bells began to ring. I got the others present on to it and watched for ca 3 mins as it passed right past and slightly behind the Runnel Stone and out of sight to the right.
Smaller than a Corys Shearwater, with direct comparisons regularly made as there were many present. Although not compared directly with one, appeared somewhat larger than Manx Shearwater.
Relatively long, thin and pointed wings. Hand was held back at a slight angle and was similar in length to arm, although probably slightly shorter. Tail was fairly long and held "clenched". Head and neck protruded clearly in front of wings but bill not visible at this distance.
The flight appeared to be clearly faster than the Corys Shearwaters. However, this was due in part at least to its smaller size and to the excessive sidewards shearing movements, which meant that in reality it didnt actually make a much faster forwards progression than the Corys. The petrel did seem to "swing" further from side to side in its shearing flight than a Manx would, probably reaching a greater height at each end of the shear. One observer claimed to have noted the bird to flip fully over, although I didnt see this. Much more buoyant and agile than the Corys.
Dark above and pale below. One observer mentioned that they could distinguish a darker cap but I couldnt make this out with my scope.
Upperwing / back
Dark grey / black. At this range, no obvious patterning could be made out.
Clearly paler grey than the back and upperwing, with the difference most visible when shearing at certain angles.
Appeared to be completely dark grey / black, with no obvious pattern at this range. However, there was clearly no pale central band. The dark underwing contrasted sharply with the rest of the underparts.
White belly / breast / undertail. Darker smudges on the breast sides were apparently noted by at least one other observer, although I couldnt personally make them out. I was, however, confident that had a breast band been present I would have been able to see it.
The size, flight action and dark underwing contrasting with the white remainder of the underparts are sufficient to identify the bird as a "Soft-plumaged" type petrel and the paler grey uppertail and lack of a breast band tend to suggest Feas (Pterodroma feae) or Zinos (P.madeira) as opposed to Soft-plumaged (P.mollis). Given the relative size of the two northern species populations, the bird was almost certainly a Feas Petrel. There currently appears to be no sensible way to separate the two species in the field at a range of 1.5 km. The date was also typical for the species.
I later checked in a number of books and articles for other features that a Feas Petrel should show. The illustrations in the new Collins Bird Guide (Mullarney et al.) are excellent in that they show a more realistic "in the field" type view of the bird than do some other books. In particular, although there is a dark "W" bar on the upperwing, a darker central bar on the underwing and a pale area on the leading edge at the base of the underwing, these are much less apparent at range and it is probably unrealistic to expect to see much at 1.5 km distance even with a good quality telescope.
Interestingly, the slightly darker bars on the upperwings of the Corys were not visible at the same range, although they were quite clear on the few dozen birds which passed at closer range. The single Mediterranean Shearwater of the morning passed at a similar distance to the Feas Petrel. Although it was a rather dark individual (and initially thought to be a Sooty), the pale central area of the underwing was clearly visible at this range and the pale central part of the belly was also visible. This observation shows that the all-dark appearance of the underwing of the Feas Petrel was reliably visible at this range.