and Ashley Fisher
was the sixth year of intensive short-range pelagic trips off the Isles
Scilly involving 50-70 trips each year with an average of around four a
(June to September). We participated in virtually every one and our
tally prior to the 2005 Swinhoe’s Storm-petrel Oceanodroma
monorhis sighting was approaching 500 trips and now is
over 700 trips. RLF has undertaken short-range pelagic trips off Scilly
seabirds is not centred purely on rarities in British national waters.
given the amount of time we spend at sea off Scilly, it was to be
that sooner or later we would encounter something out-of-the-ordinary
region. So, we identified species that we believed were the ‘more
rarities to occur and read-up on these in detail, including Swinhoe’s
Storm-petrel. Thus, if confronted with one of them we would quickly be
look for the salient features and maximise our chances of a sound
are well aware that birding at sea poses unique challenges. Sea-birding
different from land-birding. There is often little time with each bird,
opportunity to grill a find through telescopes, whilst there are many
light and weather conditions that affect the context and impressions of
seabirds. In addition, with tubenoses, we are dealing with a complex
subtle plumage problematique since
petrels are, “clad in plumage that is some combination of black, white
shades of grey and brown.” (Brookes, 2004: p.5) These challenges make
the more important to be prepared with knowledge of the salient
Circumstances and General Impression
21 July 2005
in the early afternoon
we were drifting at sea approximately 9.5 miles
(17 kms) south of Scilly. We had been
liberal with chum and an excellent slick had formed. Conditions were
for sea-birding with 100% high cloud cover and a Force 2/3
Sea-state was calm to moderate, slightly choppy with little swell. Our
birds, however, was limited to good numbers of European Storm-petrels Hydrobates pelagicus.
was scanning the slick sifting through European Storm-petrels looking
Wilson’s Storm-petrel Oceanites oceanicus
when a Leach’s-type Oceanodroma
entered his vision at about 250 metres. It swooped over the slick
upper-side. RLF’s heart missed a beat because this storm-petrel was
brown with buff covert bars on the upperwings and appeared to have an
brown rump. It looked like it could be a Swinhoe’s Storm-petrel!
calmly RLF said to EAF, “You’d better look at this petrel Ash.” EAF
immediately thinking it was yet another Wilson’s. So RLF said, “It’s an
Oceanodroma,” which sparked an
response since even Leach’s Storm-petrel Oceanodroma
leucorhoa is a genuine scarcity in Scillonian waters. EAF got
on it right
away as did John Higginson who was standing nearby. EAF helped the
less experienced sea-birders by telling them to look for a Leach’s-type
actively investigated the slick swooping from one side of it to the
back again, but its flight overall was more direct (less erratic) than
flight of Leach’s that we have seen. It tilted several times revealing
upperside and its underside. It bounded forward and one time rose above
surface perhaps to three metres and hung there briefly. The slick led
storm-petrel towards the boat and it approached to about 75 metres. It
swooped over a bit of choppy water using wind dynamics to gain lift and
towards us presenting a striking view of its upperside. EAF dared to
flight action continued in the same manner for all of the three minutes
was exploring the slick. The flight action was very exciting to watch.
the entire observation comprised the bird in foraging mode and we did
it in any other flight mode (i.e., travelling or feeding).
found size relatively
easy to judge with European Storm-petrels plentiful. Experience in
waters of Europeans alongside the larger Wilson’s
greatly assisted our assessment. Roughly speaking you could say our
was another size-step up from Wilson’s,
making it Leach’s size. Each year we see small numbers of Leach’s
amongst European Storm-petrels and the size of our Swinhoe’s looked to
be in the
region of Leach’s when compared to Europeans.
confident with our assessment of the bird’s size; however, to make a
well-founded claim of a Swinhoe’s Storm-petrel we still had to
possibility of dark-rumped Leach’s Storm-petrel and consider carefully
aspects of the bird’s field characters.
flight action and the three minute performance enabled us to evaluate
structural and plumage features. Overall, the structure of our bird was
comparable to Leach’s Storm-petrel, but with notable differences. In
the wings were held outstretched, unlike Leach’s, making the Swinhoe’s seem longer winged and a bit larger. The
hand tapered to blunt wing tips, not pointed ones. The tail often was
closed, reminiscent in side-on profile of a long tailed swift and
open, scooped and more ragged look of Leach’s. The tail fork when
visible was relatively
shallow, not as deep as Leach’s.
was darkish brown, with remiges darker. We were struck by the fact that
tail, rump and remaining body plumage were homogenous in colour. The
notably browner than European Storm-petrels that it was amongst, which
pre-moult and thus worn, bleached and at their brownest. The upperwing
displayed a warm buff diagonal covert bar across each wing that
to, but not quite up to the leading edge; it was impressive, mainly
created the only contrasting plumage feature. The warmish plumage tones
different from the cooler tones of Leach’s.
the basis of
size, structure, plumage pattern and colour, and flight action, it is
opinion that the only possible identification of the 21
July 2005 storm-petrel is
Swinhoe’s Storm-petrel. It is important to say that neither of us or
Higginson thought at any time that the bird could be a Leach’s
(see Illustration 1).
Storm-petrel off Scilly 21
July 2005 - original field sketches by Ashley Fisher.
The critical first step in identifying our bird as a Swinhoe’s
accurate judgement of size. Table 1 gives biometrics of all dark-rumped
storm-petrels and, for reference, some other seabirds. All measurements
and are given in cms. This facilitates a ratio comparison of body
wing span relative to European Storm-petrel, the commonest storm-petrel
Scilly and our ‘yard stick’. We judged our bird to be roughly the size
Leach’s. Table 1 shows that there is only one dark-rumped storm-petrel
comparable to Leach’s Storm-petrel in body length and wing span, and
that is Swinhoe’s
that there is some biometrical variation in the literature for Leach’s
Swinhoe’s Storm-petrels, but the scale of the variation does not impact
on size judgement. For example, Post (1998) measured the wing lengths
Leach’s Storm-petrels from a wreck on beaches in Portugal
and found them to be 1-5 mm longer than the
given in the literature. Cubitt (1995: 344) measured the three
Storm-petrels caught at Tynemouth (UK) in the period 1989-1994 and
“… measurements of wing length appeared to be at or beyond the extreme
documented for Swinhoe’s … This, though, appears to be due to
recorders in experience and technique of measuring maximum-chord wing
RELATIVE BODY LENGTH
Table 1. Average body lengths and wing spans
storm-petrels and other relevant species (averages, all in cms).
mainly are taken from Enticott and Tipling (1997) and are consistent
measurements from other main sources. The ‘relative length’ and
are ratio comparisons between those of an
average sized European Storm-petrel (set at 1) and the average sizes of
species incorporated in the table.
occasions off Lima, Peru RLF has seen for extended periods many
Storm-petrels (roughly the same body length and wing span as European
Storm-petrels) alongside Markham’s Storm-petrels, these two having a
of 1.53 and a wing span ratio of 1.41. The same ratios for European
Swinhoe’s are 1.33 and 1.22 respectively. It is highly relevant that
the difference in size between Markham’s and Elliot’s in the field
greater than the differences between our Swinhoe’s and nearby
Europeans. Thus, RLF
was confident that our bird was not as large as a Markham’s and thus
Storm-petrel and, therefore, certainly not as large as the even larger
Storm-petrel Oceanodroma matsudairae
or Tristram’s Storm-petrel Oceanodroma
Structure While the
size of our Swinhoe’s was comparable to that
of a Leach’s Storm-petrel, there were notable structural differences
Illustrations 1 and 2).The Swinhoe’s appeared particularly long-winged.
leading edge of the arm from body to carpal joint appeared slightly
The hands were long and tapering (as in photographs of foraging
Storm-petrel on Brian Patteson’s web site www.seabirding.com
and others in our possession). However, they were not pointed at their
all Leach’s Storm-petrels that we have seen. The leading edges of the
were slightly convex. The trailing edge of the hands appeared at times
swollen and convex suggesting a different ratio formula for the lengths
P1-P10 than Leach’s that has a straighter trailing edge to the hands;
suggested, for example, in Peter Hayman’s comparative illustration of
and Leach’s in Cubitt (1995: 348). Most of the time the Swinhoe’s wings
held outstretched, unlike Leach’s, making the trailing edge as a whole
than that of Leach’s and yielding a different longer-winged feel to the
In summary, our
Swinhoe’s Storm-petrel bounded over, swooped over, and traversed the
amongst about 30 European Storm-petrels. We found it relatively easy to
establish the size of the bird in terms of personal experience and the
dimensions given above. It was about the size of a Leach’s.
Swinhoe’s Storm-petrel off Scilly 21 July 2005 (left) and Leach’s
Storm-petrel off Scilly 27 September 2005 (right) illustrating
structural differences in the wings and tail covered in the text,
although the ragged look of Leach’s tail is not depicted here (Bob
Flood). Note that the wings of the Swinhoe’s are held outstretched
making it appear longer winged than the Leach’s (the body length
including the tail are illustrated as the same size for the Swinhoe’s
and the Leach’s).
these observations to the illustrations of Swinhoe’s and Leach’s in
BWPi, we find there is agreement except that BWPi does not illustrate
Swinhoe’s with outstretched wings and thus does not capture the
seemingly longer-winged look of Swinhoe’s (see Illustration 2). There
is a similar discrepancy between our observations and the Swinhoe’s
illustration in the Collin’s Guide (Mullarney et al, 1999). In this
respect the two guides seem to be inaccurate.
tail was quite different from Leach’s. First, the tail was forked, but
did not have the depth of fork typical of Leach’s. In step with our
observations, BWPi describes Swinhoe’s as having a slightly forked tail
and Leach’s a fairly forked tail. Indeed, this feature on our Swinhoe’s
might be better described as a notable notch rather than a shallow
fork. This feature was seen on several occasions as the bird manoeuvred
when it opened its tail. Otherwise the tail mainly was held closed.
Second, the side-on profile simply saw the tail narrow to its end.
There seemed to be no concave curvature across the width of the
upper-tail (i.e., it was not scooped) or raggedness to the tail-end,
something always apparent on Leach’s that we have seen. The tail thus
was reminiscent in side-on profile of one of the longer tailed swifts
(see Illustration 1).
summary, the body of our Swinhoe’s was about the size of Leach’s, but
the wings were held outstretched rather than swept back making the bird
look longer winged than Leach’s, and the Swinhoe’s tail mainly was held
closed rather than open, but when opened was seen to be notched rather
The entire head, body, rump, uppertail-coverts and undertail-coverts,
the tail, upperwing-coverts (except for the buff diagonal covert bars
on each wing) and, as far as we could see, the underwing-coverts were
all darkish brown. The bird was notably browner than the European
Storm-petrels, which were just pre-moult and thus in worn and faded
plumage (i.e., at their brownest; moult of adult Europeans starts
during the second half of incubation BWPi). Chris Mead (2000) in The
State of the Nation’s Birds describes Swinhoe’s as, “This browner
cousin of the Leach’s Petrel.” To be more precise, the colour of the
Swinhoe’s Storm-petrels off North Carolina on Brian Patteson’s web site
(www.patteson.com) is how we remember the colour of our bird and this
is what we mean by darkish brown.
recollect being struck by the fact that the tail, rump and body plumage
were homogenous in colour. We witnessed the Swinhoe’s in many different
flight profiles where the rump was scrutinised and seen to be wholly
and unequivocally darkish brown. Given the excellent light conditions
and multiple angles of view we feel confident that we would have seen
pale in the rump if the bird were a partially dark-rumped Leach’s. The
remiges were darker brown than the body, but not very much darker. The
upperwing displayed warm buff diagonal covert bars across each wing
that extended near to, but not up to the leading edge. The buff
upperwing covert bars stood out being the only contrasting plumage
feature. This characteristic is evident in photographs of the exhausted
Swinhoe’s captured at sea off Israel on 19 April 2003
(www.birdingisrael.com) as well as the North Carolina birds mentioned
addition, there was no obvious sign of moult or wear and certainly the
bird was not in primary moult. The bill was not seen well. The eye was
not seen well, but we presume it was black or blackish. The legs were
did not see white shafts at the base of the primaries. The literature
suggests that these are difficult if not impossible to observe in the
field unless at close range and this has been confirmed in discussion
with observers experienced with Swinhoe’s. For example, Carter and
Hobcroft (1997) noted the 15 Swinhoe’s that they located, “lacked any
visible white at the base of the primaries.” Force (1997) did not see
white primary shafts on 120+ Swinhoe’s Storm-petrels observed at sea in
the Indian Ocean. Experienced sea-birder colleagues from Australasia
rate size, structure, plumage colour, and the distinctive flight action
(all of which we saw) as the important diagnostic features (M. Carter
pers. comm.). This is a view shared by Hadoram Shirihai (pers. comm.).
Swinhoe’s Storm-petrel and not …?
is the critical factor that excludes most dark-rumped storm-petrel
taxa. Structure, plumage, and behaviour lead to the conclusion that our
bird was a Swinhoe’s. Accordingly, key points are set out below that
differentiate our Swinhoe’s from like taxa. I list my at sea experience
of each form. Here I do not mean ‘ticked’, but extended views often for
many hours spread over numerous days, thus facilitating thorough
critical examination. To start, I deal with the most obvious
identification problematique concerning the similar sized Leach’s
Nominate, about 10 off Scilly, small numbers elsewhere England over
many years, 100s in Atlantic from pelagic trips and cruises since 1990,
c50 western Pacific from cruise April 2008, c50 eastern Pacific from on
each pelagic trip mid-1990s, September 2007, and September 2008; O. l.
chapmani 100+ on five day pelagic trips from San Diego, California
September 2007 and September 2008; O. l. socorroensis 20+ believed to
have been this form on five day pelagic trips from San Diego September
2007 and September 2008.
When observing dark-rumped chapmani Leach’s off California at similar
range to our Swinhoe’s RLF was struck by the fact, as trite as it may
sound, that they looked like normal Leach’s but with a dark rump! The
flight behaviour of birds considered to be socorroensis Leach’s off
California was completely different from either Leach’s or Swinhoe’s.
In light winds socorroensis is fast and direct, rises and falls, and
tilts and flicks to either side. It has moderately deep wing beats
where the arc extends c40°-60° above and below the horizontal, probably
not as deep as Leach’s. It glides and shears for short periods. In
strong winds, socorroensis increasingly rises and falls, flicks and
tilts, glides and shears. Returning to comparison with chapmani, our
Swinhoe’s was wholly and unequivocally dark rumped but did not look
like a Leach’s. Furthermore, a Leach’s in the Atlantic with a wholly
and unequivocally dark rump is yet to be proven. With Leach’s, state of
wear and moult is important since white in the rump is likely to be
least obvious with worn rump feathers. Thus, naturally occurring
partially dark-rumped Leach’s in moult not seen well could appear
wholly dark-rumped. Such an individual might be termed a ‘pseudo
dark-rumped Leach’s’. A ‘psuedo’ in British waters might be expected
September-January, probably not as early as July when we saw our
primary foraging flight behaviour was direct and strident, with several
strong wing beats, then a bounding glide low over the sea surface.
Leach’s equivalent flight is irregular, punctuated with unpredictable
speed and/or direction changes, involving darting, vertical leaping,
and bounding ahead with frequent long shearing glides. This difference
immediately stood out on 21 July 2005. c)
Our Swinhoe’s held its wings outstretched when foraging, whilst Leach’s
wings mainly are held swept back. As a result our Swinhoe’s appeared to
be slightly longer-winged than Leach’s (see Illustration 2 above). d) Our
Swinhoe’s outstretched wings revealed the caudal projection more
clearly than in Leach’s, therefore the caudal projection appeared
longer in Swinhoe’s even though Swinhoe’s actually has a shorter tail
(see Illustration 2 above). e)
Our Swinhoe’s had blunt wing tips, whilst Leach’s wing tips are
The tail in our Swinhoe’s was held closed in foraging flight when its
shallow fork was hardly visible, unless the bird manoeuvred fanning its
tail; whilst the tail in Leach’s seems always to be open, is scooped,
and has a much deeper fork that is more readily visible (see
Illustration 2 above). g)
Swinhoe’s plumage overall was warm-toned black-brown, whilst Leach’s is
cool-toned brown-black, though Leach’s bleaches browner. Relevant here
is that Europeans also bleach browner by late July, but our Swinhoe’s
was browner still than local Europeans. h) The
secondary upperwing-covert bars were warm-toned buff in our Swinhoe’s,
whilst are cool-toned grey in Leach’s. Covert bars were less prominent
in our Swinhoe’s compared to a typical Leach’s, though would become
less distinct in a worn Leach’s later in autumn. i)
Vagrancy of eastern Pacific dark-rumped forms of Leach’s into the
Atlantic is highly improbable (see Appendix 2). Conclusion Our bird was
not a Leach’s Storm-petrel.
Petrel Bulweria bulwerii
RLF About 10 in Canary Current 1999, c20 Atlantic cruise
c25 western Pacific cruise April 2008, 100+ Madeira to Selvagens June
Size alone excludes this species with Bulwer’s very large compared to
our Swinhoe’s (see Table 1). Also, in contrast with our
Swinhoe’s, Bulwer’s jizz is like a giant storm-petrel but with unique
flight action where it zigzags, swings body from side-to-side, often
flip-changes direction, all with fairly shallow elastic-like wing
beats. It has very long wings, a long wedge-shape tail, a long slim and
lanky body, is overall sooty-brown with indistinct upperwing-covert
bars. Our bird was not a Bulwer’s Petrel.
RLF 100s with small numbers permanently on view often at
range over five days during western Pacific cruise April 2008.
Size alone excludes this species with Matsudaira’s very large compared
to our Swinhoe’s (see Table 1). Also, in contrast with our
Swinhoe’s, Matsudaira’s has the jizz of a large long-winged falcon, has
long slim wings, a long deeply forked tail, is overall dark-brown with
broad distinct upperwing-covert bars. Our bird was not a Matsudaira’s
RLF About 1000 during western Pacific cruise April 2008,
numbers permanently on view one afternoon at close range, small numbers
next day, and numerous birds again on the following day.
Size alone excludes this species with Tristram’s very large compared to
our Swinhoe’s (see Table 1). Also, in contrast with our
Swinhoe’s, Tristram’s jizz is somewhat like a very small Pterodroma,
has long wings, a long deeply forked tail, is thick-set with a long and
solid body, is overall sooty-black with bold upperwing-covert bars. Our
bird was not a Tristram’s Storm-petrel.
Experience RLF Many
100s seen from pelagic trips out of Lima, Peru almost annually since
Size alone excludes this species with Markham’s large compared to our
Swinhoe’s (see Table 1). Also, in contrast with our
Markham’s jizz is like a large kestrel, has very long wings, a very
long deeply forked tail, and a long slim and lanky body. Our bird was
not a Markham’s Storm-petrel.
RLF Many 100s seen from pelagic trips on 13 days
out of San Diego
and Monterey, California September 2007 and September 2008;
storm-petrels thought to be Black observed amongst Markham’s on a
number of pelagic trips out of Lima, Peru since 2000.
Size alone excludes this species with Black large compared to our
Swinhoe’s (see Table 1). Also, in contrast with our
Black has a Black Tern-like jizz, long wings, a long deeply forked
tail, a long and lanky body, is overall rich black-brown. Our bird was
not a Black Storm-petrel.
Experience RLF 1000s
seen from pelagic trips on eight days out of Monterey, California
September 2007 and September 2008.
In contrast with our Swinhoe’s, Ashy jizz is rather like a small
kestrel, has much shorter wings that it tends to hold more swept back,
has a long deeply forked and scooped tail, is quite chunky bodied, is
overall ashy-black with distinct but greyish upperwing-covert bars. Our
bird was not an Ashy Storm-petrel.
Experience RLF About
20 over three days on five day pelagic trip San Diego, California
September 2007 and September 2008.
Size alone excludes this species with Least very small compared to our
Swinhoe’s (see Table 1). Also, in contrast with our
Least has a rather bat-like jizz, tends to hold its wings more swept
back, has a medium-short rounded wedge-shape tail, is overall
sooty-black with indistinct upperwing-covert bars. Our bird was not a
this note we have reported a sighting off Scilly on 21 July 2005 of
what we are certain was a Swinhoe’s Storm-petrel. Swinhoe’s
Storm-petrel breeds in the Northwest Pacific Ocean, but since 1983
records of Swinhoe’s in our region have come from Britain, France,
Madeira, Norway and the Mediterranean coasts of Spain and Italy. There
are four records for North Carolina, USA. Indeed, to date in the
Atlantic and neighbouring seas 23 Swinhoe’s have been recorded most of
which were trapped (several DNAd) with 18 accepted formally by national
panels, plus five other well documented at sea records Also, Swinhoe’s
has been recorded five times off Eilat, Israel. There have been several
recaptures including the original 1983 bird on Selvagens 24 years later
at the same sight! Swinhoe’s Storm-petrel routinely frequents the
Atlantic and neighbouring seas, albeit in small numbers. Our record,
then, is far from extraordinary, whereas a record in these seas of a
wholly and unequivocally dark-rumped Leach’s or any other candidate
all-dark storm-petrel would be unprecedented (save for one Matsudaira’s
Storm-petrel off Cape Town, South Africa on 25 March 2002).
believe that our identification of the Scilly Swinhoe’s Storm-petrel is
sound based on our observations, our experience, our preparedness, and
that there is adequate knowledge about the differences between
Swinhoe’s Storm-petrel, Leach’s Storm-petrel, and other dark-rumped
storm-petrels to facilitate at sea identification given adequate views
(see Howell & Patteson, 2008).
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November 1999. (Unpublished) Submitted by M. Carter and D. Hobcroft.
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