Er wordt in de discussie gevraagd om reacties van de ontdekker(s). Die reacties zijn zeker wel gegeven. Zie hieronder mijn reactie en het commentaar van Bob Flood van een paar jaar geleden (in rood-cursief). In deze comment ook een betere grootte-vergelijking dan deze poging hierboven met onscherpe Kokmeeuwen (natuurlijk zijn t Kokmeeuwen). 

BULWER’S PETREL ON THE WESTPLAAT IN AUGUST 1995

Original Dutch submission translated into English by Jan van der Laan.

Comments & opinion by Bob Flood (RLF).

I have summarised the observers’ notes under key headings and where relevant provide comments on their observations for each key heading. This helps further consolidate the observers’ description and my comments into distinct categories. A caveat here is concern that a few of my worries may arise due to problems in direct translation of subjective descriptions from Dutch to English. My comments mainly concentrate on identification matters relating to Bulwer’s Petrel and the only other likely confusion species Swinhoe’s Storm-petrel. I have extensive experience of Bulwer’s Petrel and all species of all-dark Oceanodroma storm-petrels, except I have witnessed only one Swinhoe’s Storm-petrel at sea. In my evaluation of the submission I have compared the observers’ description of flight behaviour to my video of Bulwer’s in all kinds of wind conditions and a colleague’s video of Swinhoe’s in similar conditions to those of the Westplaat 21 August 1995. I provide an opinion at the end of the document.

Background:

Summary: The date was 21 August. The sky was clear and thus conditions were sunny. There was a light breeze over Westplaat rising to a moderate breeze later as the petrel headed out to sea. The petrel was observed for more than one hour occasionally at a distance of about 50 metres, though more often at 200+ metres.

Jizz:

Summary: Reminiscent in flight and posture of a Swift Apus apus, also described as a large and plump swift, due to the combination of slender body, long wings, long wedge-shaped tail, and powerful wing beats. Possibly perceived to be falcon-like by proximate shorebirds and gulls since these birds were flushed by the petrel as it approached them.

Comments RLF: Jizz is subjective, but I would not describe Bulwer’s as reminiscent of a Swift, which admittedly is long winged and fairly long tailed. Bulwer’s glides a lot more than Swifts and flaps wings less frequently in a less rapid fashion. In fact, Bulwer’s in calm conditions like those of 21 August 1995 can look quite lazy in flight, a bit like a Calonectris shearwater. Equally, Swift and Swinhoe’s do not resonate well with each other. Perhaps the observer meant only his instant first reaction was Swift, which is more understandable. However, falcon-like is a passable analogy for either petrel.

Indeed, analogy with a Swift was a first impression made from long distance (200m). It emphasises the long-winged impresson of the bird and his long tail, though, (combined with its flight behaviour). With an Oceanodroma, a comparisson like this, I think, would never have been made because of its broader wingbase. None of the observers had experience with Swinhoes'  but all of us have certainly seen many Leach's, which never struck me as swift-like. A lot of other observers saw the bird later from great distance. To them the bird was' Shearwater-like', no one ever compared the bird to an Oceanodroma.

Size:

Summary: The petrel was compared in size to Common Tern Sterna hirundo where the petrel’s wing span (WS) was estimated at two-thirds (67%) that of Common Tern.

Comments RLF: Typical biometrics in the literature are Common Tern WS 77-98, Bulwer’s Petrel WS 68-73 (c.80% that of Common Tern), Swinhoe’s Storm-petrel WS 44-46cm (c.50% that of Common Tern). Estimate in WS falls nearly half way between Bulwer’s and Swinhoe’s. At c.50% of the wing span of Common Tern I would expect a Swinhoe’s overall to look decidedly small adjacent to a Common Tern such that the observers certainly would have commented on this. The observers’ estimate of size is better for Bulwer’s that would look somewhat smaller than Common Tern, though never decidedly small.

It was a large Common tern apparantly. In my memory the bird looked medium sized but certainly not small.

Structure:

Summary: Head small with a short bill. Wings long and slender with fairly blunt tips that were blunter than wing tips of Common Tern. Caudal projection was greater than head projection and the same as wing width at wing base. Tip of the tail appeared variously square and rounded. It is claimed that that wedge shaped tail is visible in photographs though was not conspicuous in the field.

Comments RLF: The head of Bulwer’s is small, but the head projection is long and I would have expected the observers to mention this. Was the short bill Bulweria-type or storm-petrel-type? At 50m I would have expected the observers to note something in this regard. Bulwer’s wings are exceptionally long for a petrel. It is a feature that strikes me every time I see a Bulwer’s. I am surprised that the observers did not amplify this point (if the bird was a Bulwer’s) stating only that the petrel had long wings. Arguably, a Swinhoe’s could be described as long winged. Wing tips in Bulwer’s surely are pointed quite like those of Common Tern, not fairly blunt as in the description of the Westplaat petrel. Wing tips in Swinhoe’s may be described as fairly blunt. The observers noted the caudal projection longer than the head projection, which is correct (also correct for Swinhoe’s); but they also noted the caudal projection the same length as the wing width at wing base, which is incorrect and more like Swinhoe’s. The caudal projection in Bulwer’s is very long and obviously longer than the wing width at the base. I can accept that the wedge shape of a Bulwer’s tail in the field is not always conspicuous and may appear variously square and rounded at times.

And what about the forked tail of Swinhoes? A forked tail would definitely show in a Leach's in two hours of observing such a bird. The same holds true for Swinhoes, I expect. The description of the tail is completely wrong  for a Swinhoes. Furthermore I would not describe a Leach's as long winged and remember the bird as being clearly much longer winged than an Oceanodroma, in fact, that's the main reason why we immediately disregarded the bird as belonging to one this taxa. I don't remember exact proportions of tail vs wingbase or exact form of he bill.

Plumage:

Summary: Sooty-brown overall. A pale chin head-on at close range looked like a pale spot. Rump was dark. Pale band across secondary coverts comprised pale tips of secondary greater-coverts with secondary median-coverts a shade lighter than remiges. Pale band was visible up to 300m. Visible at very close range was a pale grey quarter-width band across secondary greater-coverts on the underwing, stronger on the arm than the hand.

Comments RLF: The description of plumage appears generally accurate for Bulwer’s, especially with the pale chin that you would not expect to see on Swinhoe’s. The cheeks and upperthroat typically are paler in Bulwer’s. I would have expected the observers to describe the upperwing band in terms of pale secondary greater-coverts, not pale tips to secondary greater-coverts. The distance at which the pale band on the upperwing was visible equates with my experience of Bulwer’s. If the petrel was a Swinhoe’s, I would have expected the observers to see white bases to primary shafts of the outer primaries given the duration and closeness of observation. It is possible to see a silvery reflection coming from the underside of the remiges of Bulwer’s in strong light that reflects off the sea and the underside of the remiges, but this is not a pale band across the secondary greater-coverts as described by the observers. However, it may have been tricky for the observers to detail this feature on a mobile bird.

The Westplaat-sighting is precedented in 1993 in Europoort by another Bulwers', picked up alive from a ship (Moeliker in DB:18(5): 231-234). It later died. This bird had a light band on the secondary greater coverts on the underwing exactly as described for the Westplaat bird..

Flight behaviours:

Summary: In gentle (“soft”) northeasterly breeze: Foraging flight Sudden changes in flight direction described as erratic, but also described as weak banking. Flight described as bouncing. Consistently flew low over the sea surface. Typically 5 wing beats were followed by gliding with wings stiff, pushed downwards, slightly angled. Number of wing beats and duration of glides were irregular. Also wings said to be held level with surface when gliding. Wing beats powerful and reasonably fast. Wing beats slower than Manx Shearwater Puffinus puffinus recalling Arctic skua Stercorarius parasiticus. Feeding behaviour Apparently “paddled” across the surface (presumably sea) with wings raised like a Leach’s Storm-petrel Oceanodroma leucorhoa. Fed along the edges of the sea and mudflat. On one occasion spent c.15minutes feeding over the mudflat. Collected food items from the mudflat with legs stretched, tail spread, and wings “held somewhat thrown in”.

Comments RLF: Foraging flight The terms “erratic” and “bouncing” used by the observers do not equate with my experience of Bulwer’s foraging flight in relatively calm conditions. The terms ‘twisty’ and ‘buoyant’ are more indicative of Bulwer’s foraging flight in calm conditions and perhaps this is what the observers meant? Bulwer’s do typically remain low over the sea surface on long glides interspersed with 1-5 wing beats with “weak banking”. I have consistently noted Bulwer’s wings more bowed in flight than Oceanodroma storm-petrels, but this was not noted by the observers. I would not use the following terms for wing beats in calm conditions, “powerful” and “reasonably fast”. As said earlier, Bulwer’s in calm conditions like those of 21 August 1995 can look quite lazy in flight, a bit like a Calonectris shearwater. The comparisons given against Manx Shearwater and Arctic Skua seem reasonable for Bulwer’s. Feeding behaviour Typical biometric in the literature are Bulwer’s tarsus 24-30cm, Swinhoe’s tarsus 22-23cm. Thus, dangling legs would have looked pretty short in Bulwer’s and in proportion with Swinhoe’s, but the legs were described as “stretched” without a clue given about length. Feeding behaviour is extraordinary for Bulwer’s or indeed Swinhoe’s. However, “paddled across surface with raised wings like a Leach’s Storm-petrel” is hard to equate with Bulwer’s and, of course, is quite easy to equate with a storm-petrel like a Swinhoe’s. I am familiar with Leach’s Storm-petrel feeding on the tideline and flying over beaches in stormy conditions. Such behaviour of the Westplaat petrel, albeit in calm weather, is thus marginally in tune with a storm-petrel, though seems incompatible with everything I know about the feeding behaviour of Bulwer’s Petrel. Note that I do not understand the meaning of, wings “held somewhat thrown in”.

The translation of the Dutch text into english would not have been mine. I don't read the Dutch synonyms for "erratic" (erratisch) or "bouncing" (verend). The description of Bob: "...Bulwer’s do typically remain low over the sea surface on long glides interspersed with 1-5 wing beats with “weak banking”...is actually almost wordly how the flight is described in the article of Aat. The bird was often changing direction and had an irregular amount of wingbeats (mostly 5), that is translated with "erratic". With an Oceanodroma like Leach's (and most probably Swinhoes) you would expect flight being described as fluttering, swinging, hesitant, with sudden drops, quick soarings and angles.This terms were never used.

The Westplaat bird was probably taken in by a ship and was probably hungry. It has started feeding immediately after reaching Rotterdam but in a total unsuitable feeding habitat, a shallow mudflat instead of a deep sea. This explains most of its unusual behaviour in its feeding techniques. So we can not project 'normal' behaviour one to one with this birds'.

 Summary: In wind approaching Beaufort 5: Travelling flight Flew in straight line, close to surface, and sheared/banked like a Puffinus shearwater, with deep 90 degree arcs, thus occasionally visible above the horizon.

Comments RLF: Travelling flight The terms “erratic” and “bouncing” would describe fairly well Bulwer’s in moderate wind, but these terms were not used to describe the flight of the Westplaat petrel as it headed out to sea when the wind was Beaufort 5. That said, the description of travelling flight in a straight line and shearing equates well with Bulwer’s. However, such travelling flight is also accurate for medium- and large-sized Oceanodromas in moderate winds. Indeed, we experienced difficulty in the Pacific separating shearing Bulwer’s from shearing large Oceanodroma storm-petrels in moderate winds at distances of 300+ metres.

Surprising, because of its long wings at 300m I expect Bulwers to look more Shearwater-like, as seen in the Westplaat-bird. I would say that Leach's (and Swinhoes?) do not bank like shearwaters but much less deep and with much quicker movement (unlike the Westplaat bird). I'm not completely sure though if Oceanodroma petrels never resemble such long winged, higher banking, petrels/shearwaters.

Elimination of other species:

I agree with the observers’ discussion about the elimination of Jouanin’s Petrel Bulweria fallax and dark morph Wedge-tailed Shearwater Puffinus pacificus.

Experience of observers:

Unfortunately the experience of the observers with Bulwer’s Petrel and all-dark Oceanodroma storm-petrels is not given in the description. This is very important to know in the context of this record.

Photographs:

There are two photographs in the submission. The top photograph showing the petrel with fuzzy edges has to be interpreted carefully. However, the image suggests very long slender wings, very long caudal projection, and a wedge shaped tail. It most resembles a Bulwer’s Petrel. The bottom photograph could be a Bulwer’s or indeed a Swinhoe’s. For example, compare it to George Armistead’s (top photo) ‘equivalent’ quality photograph of a Swinhoe’s on page 75 of Blomdahl et al’s Flight Identification of European Storm-petrels (Helm 2003).

Opinion:

This is an incredible if not bizarre record. It must have been an extraordinary experience for the observers. Indeed, without the photographs a commentator could be excused for thinking that the observers had somehow made a fundamental mistake and were not watching a petrel/storm-petrel at all. However, the photographs conclusively show the bird was a petrel/storm-petrel of some kind and the photographer deserves some credit in this regard. So, what kind of petrel/storm-petrel was it?

My opinion based on the written and photographic evidence presented to me is that we will never know for sure the true identity of this petrel/storm-petrel. The fatal problem in this regard is the contradictory nature of the submitted evidence. I have provided detailed comments above for each element of the observers’ description. A systematic read of my comments should leave the reader in no doubt that some of the evidence points to Bulwer’s, some evidence to an all-dark storm-petrel (most likely Swinhoe’s), whilst there is some evidence that could describe one or other of Bulwer’s or an all-dark storm-petrel. Some of the description simple seems wrong for either one or the other. Here are some examples:

• A swift analogy would not be my first choice for Bulwer’s or Swinhoe’s.
• Estimate of size is better for Bulwer’s though not perfect.
• In the main description of structure better supports Swinhoe’s, with the exception of wedge shaped tail.
• The description of plumage in general could be either Bulwer’s or Swinhoe’s with two important exceptions. The pale throat is typical of Bulwer’s and not Swinhoe’s. Pale on the underwing might be seen in Bulwer’s, though note that how this is detailed in terms of pale feathering on the underwing is incorrect.
• Some aspects of travelling flight behaviour describe typical Bulwer’s flight whilst other aspects seem incorrect for Bulwer’s. Feeding flight behaviour seems atypical of Bulwer’s and some aspects seem very accurate for a storm-petrel.

In conclusion, this submission falls far short of what is required to add Bulwer’s Petrel to the Dutch list.

Bob Flood

Isles of Scilly

29.11.2008

My opinion: A fair comment on the translated text of Aat in DB.

Indeed, some characteristics could have been emphasized or described more carefully. While observing the bird we immediately disregarded small petrels because of size, long wings and tail and strong wingbeats.This has undoubtly influenced the description and its accents, given by Aat. Still I'm absolutely convinced that the bird was not a Swinhoes( if this species is as I think it is: a dark Leach's).For me it's unthinkable that four experienced birdwatchers watch a dark Leach's petel for two hours and not consider it seriously to be one. There are about 30 other observers of this bird and no one ever mentioned a small petrel.

My only frustration with this great sighting is that I know that if only Bob would have been 10 seconds at the sighting or that if Bernd had spend a little more money on his photographic equipment  none of the letters of this writing would ever have seen  paper. I disagree about the underwing pattern and the flight characteristics being wrongly described and must strongly mention that the unusual habitat is also a factor which could have influenced this bird's behaviour.

I think with this extra information provided by Bob, this comments and Aats article in DB and because of Bobs' introduction in which he states that Swinhoes is the only likely confusion species, Swinhoes can be ruled out after all, and the submission is still standing strong as before.

 I think it would be very unwise to skip this spectacular sighting and disregard this record only because its an honestly, not completely spotless, described, field record.

Matsudeira’s of toch een Swinhoe’s? Mister Israël en inmiddels niet onbekend met zeevogels gaat voor de eerste.