An atypical
American Golden-Plover
(Pluvialis dominica)
on South Beach, Chatham,
Massachusetts
1 & 3 May 2005
Postscript: This bird was still present on 14 May, by which time it had progressed farther into alternate plumage, showing more extensive black on the flanks and under the tail, as well as a white bulge on the sides of the neck, features that would seem to indicate the bird was in fact an American, not a Pacific as first suspected. The discussion below was written prior to this revelation.
These seven images were digiscoped with a Leica Televid 77 scope and Nikon Coolpix 995
camera, late in the day on 1 May under overcast conditions. These images have
been cropped somewhat, sharpened, and the contrast adjusted, but are otherwise
unaltered.
Two additional photos taken on 3 May 2005 with a Canon 20D and Canon 100-400
IS Lens (these are heavily cropped), late in the day in full sunlight.
All images taken by Blair Nikula.
Discussion:
I observed (and photographed) this bird for about
half an hour on 1 May at distances ranging down to about 100 feet under overcast
conditions, and for about 5 minutes on 3 May at distances ranging down to about
150 feet in bright sunshine. I saw the bird in flight several times, though
never very well (i.e., flying directly away, and/or in poor light, or low to the
ground making it difficult to see the underwings well). However, I saw it well
enough to see that the underwings were dusky, not white, and that the upperwings
and tail were uniformly golden-brown, with no wing stripe, thus
eliminating the possibility of European Golden-Plover (P. apricaria).
Despite seeing the bird fly several times, I never heard any sound from it, nor
was I able to determine whether there was any toe extension beyond the tail.
Although I have extensive experience with American Golden-Plover (P. dominca), my experience with Pacific is very limited. I saw the April 2002 bird on Plum Island (Massachusetts), and saw both forms on the breeding grounds in Nome, Alaska in 1987 (before the two forms were split).
Following
my discussion below, I have appended comments from several people who have
viewed the photos and offered their impressions.
Identification of the South
Beach plover:
Separation of Pacific and American golden-plovers in
any plumage other than full alternate is difficult at best and in some
individuals (such as this one?) probably is not possible. Virtually all of the characters distinguishing the
two species are variable and most overlap to some degree. However, the salient
features of this individual seem either to be correct for Pacific or to lie
within the range of overlap with American. I can see no features that would
eliminate Pacific, while some features appear to be outside the range of
American (with the caveat that some of the important mensural characteristics,
such as bill length, tarsus length, and projection of folded primaries beyond
tail tip, cannot be determined with certainty in the field or from the photos). Some of the
features of the South Beach plover discussed below (especially primary
projection) were difficult to determine in the field and are based upon
examination of the photos.
One of the most recent papers on the identification of these sibling species is that of
Johnson & Johnson (hereafter J&J), published in the Wader Study Bulletin in April 2004 (“Morphometric
features of Pacific and American Golden-Plovers with comments on field
identification”). This paper is available online at: http://web.uct.ac.za/depts/stats/adu/wsg/pdf/wsgb-apr2004-golden-plovers.pdf.
The authors have been studying Pacific Golden-Plovers for over two decades,
capturing over 600 individuals since 1979. The following discussion draws heavily
from the Johnson’s work as well as a variety of other sources, including
Byrkjedal & Thompson (Tundra Plovers, 1998), the
web site of Hugh McGuinness discussing the bird on Long Island in September 2003:
http://mail.ross.org/~hmcguinness/East%20End%20Birds/EEBphotos/PGP.htm
and the web site of Angus Wilson discussing the bird in New Jersey in September
2001: http://www.oceanwanderers.com/NJPGP.html
Features that have been used to distinguish these two
similar species, in addition to the distinctive alternate plumages and calls, include: bill size
(particularly length), tarsus length, primary length (relative to tertials and
relative to tail tip), relative lengths of the ninth and tenth primaries, and
tertial length (relative to tail length). However, in their paper, J&J conclude that many of these features,
such as tarsus length,
overlap to such a degree that they are not reliable for identification.
Plumage: The South Beach plover is in at least
a partial, and perhaps nearly complete alternate plumage. The dorsal plumage is
a mix of gold-spangled alternate feathers and plain brownish basic feathers.
Likewise, the underparts are a mix of black and white feathering. It appears to
me that the bird may still be molting, as some of the wing coverts look new and
not fully grown. J&J state that the pre-alternate molt in both
species is generally completed by mid April. If the South Beach bird is near the
end of its molt, then it is almost certainly either a female or a first-year
bird. The absence of any black in the
undertail coverts in early May seems highly unlikely in an adult male American,
and is probably atypical for a female as well. The black on the
flanks, while more typical of American, does apparently (based upon a number of
photos published in print and online) occur in Pacific as well and thus could be consistent with either species, depending upon the sex or molt
state. The width of the white neck stripe,
which still has some brownish basic-type feathers mixed in, is difficult to
determine in this case, though to my eye it looks somewhat more consistent with
Pacific (i.e., the white being narrower than on American). It has been suggested
that in alternate plumage, the gold spots on the dorsal feathers of Pacifics are
larger and the white markings smaller; the alternate feathers on the dorsum of
the South Beach bird show very little white. In sum, though not conclusive due
to uncertainty about the sex and molt state of the bird, the plumage seems a
better match for Pacific, most likely an adult female.
Bill Structure: Pacific Golden-Plover has a
longer bill, on average, than American, though there is extensive overlap (and
females average slightly shorter than males). J&J found that
the length of the bill was greater than the distance from the base of the bill
to the back of the eye on 91% of Pacifics and 62% of Americans. The average
difference in these two measurements was 2.6mm on Pacifics (n=40) and 1.6mm on
Americans (n=18). On the South Beach plover, the bill, if folded back from the
base, extends well behind the eye (see enlargement below). Using published bill lengths in J&J, I estimate the difference between bill length and base of bill to back
of eye distance of the South Beach bird to be at least 3.5mm and perhaps as much
as 5.5mm, strongly suggestive of Pacific.
Tarsus Length: One feature of the South Beach
plover that initially troubled me was that it seemed to lack (both in the field
and in most of the photos taken on 1 May) the “long-legged” look that has
frequently been cited as an important feature of Pacific versus American. Though often touted as a key feature in separating these two forms, Pacific
purportedly being consistently longer in this measurement,
J&J
found that, although Pacifics do average somewhat longer in tarsi (again,
females average slightly shorter than males), there is extensive overlap. In
fact, the shortest Pacific in their sample was shorter than the shortest American. Samples from
other locations in the Arctic found similar variation and one sample of 38
Americans from Churchill, Manitoba had an average tarsus length that exceeded
the average of any of the Pacific samples published! Thus, they conclude that tarsus length
cannot be used to separate these two species.
Tibia Length: J&J found a
significant difference in the length of the unfeathered tibia, Pacific averaging
4mm longer than American. However, there again is considerable overlap, and this
feature is very difficult to determine in the field or from photos, the degree
to which the tibia are visible varying with the posture of the bird.
Primary Length: One of the key features
separating the two species is the relative length of the primaries, American’s
being longer; there is almost no overlap in this character, though it is a
difficult feature to determine in the field. On Pacific, two or three primaries
project beyond the tertials, while in American four or five primaries project
beyond the tertials (J&J confirm this oft-cited character). In
the field, I could be sure of only two primaries projecting, though I suspected
there might be a third that I wasn’t seeing well. The photos (see blow-up
below) clearly show
three primaries projecting, with P9 being almost equal in length to P10 and thus
being difficult to see. The fact that P9 is almost equal to P10 is another
feature typical of Pacific, though J&J conclude that variation
in P9 length results in considerable overlap, making this feature unreliable.
They found an average difference of 2.7mm in Pacific and 5.0mm in American; the
difference in the South Beach bird is almost certainly <2mm, and thus much
more Pacific-like.
Another way of examining
primary length is to compare the extension of the primaries beyond the tail,
again American showing more projection. J&J found that on Americans, the primary extension beyond the tail
ranged from 12-22mm (n=34), while in Pacific the range was from 0-9mm (n=50).
However, these figures are estimates made from observations in the field with
binoculars or telescopes, not actual measurements in the hand. Obviously, wear
in the primaries would also affect these measurements.
Getting
really anal, I measured the primary projection in the first photo of
the South Beach bird as a percentage of the bill length, then calculated the
possible range of the projection length based upon the range of bill lengths
(both species) published in J&J, I come up with a range of about 11-16mm for
the primary projection of the South Beach bird. In other words, the South Beach
bird has a bill length/primary projection ratio of about 5/3, so if its bill is
extremely short (20mm), then the primary extension is about 11mm, but if the
bill is at the long extreme (26.6mm), then the primary extension is about 16mm,
which places it beyond the range of Pacific and at the short end of the range of
primary extension estimated for American by J&J. However, I also applied
this technique to the photo of a female Pacific in Byrkjedal & Thompson (pg.
70) and came up with a primary extension range of 14-19mm, again well beyond the
supposed range of Pacific. Likewise, the Pacific illustrated at this web
page
shows a
similar projection beyond the tail (note also the very short tertials on this
bird). So, either my reasoning is flawed, J&J's
estimates are flawed, the photos in Byrkjedal & Thompson and on the Asian
web site are misidentified, or
primary projection beyond the tail is much more variable than J&J
suggest. J&J also suggest that
the ratio of primary projection to bill length is <½ in Pacific and = or
>½ in American; the South Beach bird matches American on
that basis.
Tertial Length: Pacific has, on average,
longer tertials than American, the tertials typically extending to at least
⅔ of the tail length in the former and generally less than ⅔ in the
latter. This is another variable and unreliable character, made all the more so
because it is difficult on a sitting bird to determine exactly where the tail
begins (anterioraly). The J&J paper includes two photos of
alternate-plumaged male Pacifics on which the tertials extend only about halfway
out the tail. I judge the tertials on the South Beach plover to extend about ⅔ the length of the tail.
In summary, most of the salient features on the South
Beach plover are consistent with Pacific; one feature, the
primary extension beyond the tail, is suggestive of American, though it is
unclear if that character is reliable. Although I have very little experience with Pacific Golden-Plover,
from the time I first saw this bird in the distance there was something
unsettling to me about it’s
overall appearance. It just did not fit my conception of an American
Golden-Plover. I was also struck by how difficult it was at times to pick out of
the numerous Black-bellied Plovers with which it associated, unlike typical
American Golden-Plovers in my experience. However, it was only after examination of the photos and a review
of the literature that I became convinced that it was Pacific Golden-Plover.
Several people generously (and courageously!) offered comments, which I have reproduced (with minor editing) below. Opinions about the identity of the South Beach bird are quite divergent, to say the least!
Steve Mlodinow (5/6/05): The primary extension would be exceptionally long for PGP. Also, the black on the lower flanks argues against PGP (I just saw a photo-essay in a back-issue of Western Birds -- sorry don't have volume number available -- that had a similar bird ID'd as a AGP). Given the presence of black in a location atypical for PGP and the quite lengthy primary extension, I think this is an AGP, perhaps a first year bird.
Steve
Mlodinow (5/9/06): My comments regarding
the bird's underpart plumage were not meant to imply that they were diagnostic
for AGP but merely that they were not inconsistent with this conclusion.
Certainly, a PGP could appear this way beneath.
Molting golden-plovers, or birds in incomplete alternate
plumage, are often unidentifiable.
And though I've heard of, and seen apparent photos of,
long-winged PGPs, this bird is very long-winged, and I'd be surprised if it were
within the range of PGP.
RE: Jizz. Our comments about apparent shape. I'm always
rather wary of such from photos; at least there was more than one and they are
of good quality. To me, the jizz of this bird is not that of a PGP. Its legs
don't look quite long enough. The bill seems intermediate. But these are weak
marks.
Impossible that this is a PGP? Perhaps not. But combine the
very long wings with the ambivalent underpart markings and the bird's location,
and the liklihood of the bird being a PGP becomes quite small.
Curtis
Marantz (5/6/05): When
I looked at your photos and read your commentary, I was struck by how good the
bird looks for Pacific structurally, but I'm not sure the plumage characters are
as good. To me, the white on the sides of the breast seems broad and rounded,
more like American, and the blotches of black on the belly and flanks seem to
come right up to the wings, both of which I'd say favor American. The bill size
looks okay for Pacific and the wings do look short to me. I must admit, though
that I really hate these transitional-plumaged golden-plovers because they
really are a pain and one can never really tell how it will look when the full
alternate plumage comes in.
I remember back to
the PI [Massachusetts] bird that many argued that the early stage of molt
(basically in almost full, alternate plumage in April) was good for Pacific,
which molts earlier (at least in part). By contrast, the later stage of molt in
your bird seems more like an American, which often remain in mostly basic
plumage well into migration. That said, a first-alternate Pacific is probably
going to look about like what you had through the summer, as you noted.
Additional things that complicate matters are the fact that
worn tertials may make the primary projection look longer, but missing or
incompletely molted primaries will result in projection looking shorter. Given
that date, I doubt that the bird is molting the longest primaries (especially
both of them at once). Taken together, I'd probably go with the structure of the
bird supporting Pacific over the plumage which may be equivocal or tending
slightly towards American. Given the extreme rarity of Pacific on the east
coast, I'm not sure I'd accept a record as such, but my inclination is that the
bird is a Pacific, and it is probably at least as well documented as the bird on
PI (which I myself looked at for three hours, though never as a distance as
close as you observed your bird).
P.S. The bill measurements that you mentioned seem awfully
large, suggesting to me that they are taken from the base of the bill at the
skull. If so, much of the measured part may be hidden by feathers, which in part
may explain the problem that you had with your comparisons.
Rick
Heil (5/6/05): I'm not at this time
convinced that this is fulva. Structurally it appears more dominica to me. Legs
don't look excessively long to me in most of the photos. The bill does look long
like fulva but probably doesn't eliminate dominica, I think. Some black
feathering coming in on the flanks is a dominica feature as is the apparent
extensive white "blob" out onto the breast sides. I would expect SY+
fulva to be in more advanced state of molt by now, nearly in alternate. Dominica
in May, I think, are often in a similar state of transitional plumage to this
bird. State of molt more typical for dominica for this date. Despite the fact
that I can only count 3 primaries beyond the tertials, and P10 and P9 are very
close together (both features are excellent fulva characters) the tertials still
seem short. But maybe some tertials are broken or worn? Fresh tertials in fulva
often extend nearly to, or to, tail tip. Note that all three primary are at
(apparently P8) or extend well beyond the tail (P9 and 10) on this bird, not
typical for fulva. However, if this is dominica, why aren't there the typical
4-5 primaries showing beyond the tertials? Was it missing any primaries (like
P7) when seen in flight? So in sum this is a confusing bird and therefore I am
not yet ready to say it is definitely fulva or dominica, but currently lean a
bit towards the latter.
I haven't yet read the J&J paper so may revise some
comments (and opinion) when I have.
Richard
Crossley (5/6/05): I don't know if your
bird is still present but I would encourage people strongly to go and see it. I
prefer to see birds in the field than photos, particularly just one.
Bills and legs are of no importance in my opinion (contrary
to literature). Tertial length, wing point, primary projections and spacing show
variation, sometimes extreme but this pattern is very much Pacific.
There is a lot of white towards the upper breast but the
shape is not classic American and I would prefer not to have black protruding
through the white flank line for Pacific but all in all I think fine for
Pacific. Extensive white undertail strongly Pacific.
Supercilium on Pacific tends to curve down quicker with a
broader dark nape line - this can be striking at long range in direct comparison
- appears to show this.
The most striking feature in the field is structure. Although
they can look remarkably tall and slim, typically they look fat and big headed
(and big eyed) - at times remarkably Black-bellied like - probably enhanced by
superc. shape.
Adult assumedly female, probably close to the end of its
molt. I hope its still there and you got to see it.
Julian
Hough (5/8/05): Blair's bird is
interesting and I found it a tough call, since none of the features jump out as
good for either species. Structurally it looks good for fulva as do the unmarked
vent, and if anything, the upper flank area seems to have one or two
"chevron-shaped" dark bars sitting quietly among all the solid black
area. If this were a bird further into breeding dress, I feel that these bars
would be in an area on the upper flanks consistent with fulva.
I initially thought it was a funny dominica, but on closer
looks and Blair's description it could well be fulva. The flank bar and white
undertail coverts sway me toward fulva. Fulva can show black undertail coverts
like dominica, so any bird showing colour here could be either. Since the
Monomoy bird is pale-vented, I'm unsure how diagnostic this is for fulva. Can
dominica's show pale-vents like this? The width of the dark-neckstripe (broader
on fulva) is hard to judge and the wingpoint and bill is sort of inbetween and
doesn't help me much.
Having seen both species, both as vagrants (in the Uk) and on
breeding and wintering grounds, I found that many of the photos I have seen of
vagrant fulvas seemed to be relatively straightforward. I always thought I'd be
confident in calling one here in CT, but I'm glad I didn't find this one....!
One to talk about rather than panhandle an opinion.
If I saw this in CT, I'd be hesitant to put a name to it
straight away, but I'd be calling people to look at it.
Interesting that it hasn't generated more discussion.
Alvaro
Jaramillo (5/9/05): I would go for
American on your bird although a real short-winged one. The short wings are the
main issue of confusion for me, the rest of the structure (part short legs) is
typically American. The white undertail covs are not a big issue as female
Americans are often white here. However the black feathers on flanks are fine
for American, and argue against Pacific. I have been to Hawaii 3 times in the
last couple of yrs and have been able to study hundreds and photo a lot of basic
Pacifics. The overall golden colour of upperparts is pervasive, particularly on
scaps but even on coverts. All of the basic type feathers on your bird are dull,
some with nice whitish fringes, this is typical of basic American but not
Pacific. If a Pacific, many of the old scaps would show golden fringes. The
fresh primaries also point to American as someone else suggested. Sorry I can't
go into more detail and that this note is so disjointed, when I have my other
hand back I can e-mail you some photos showing typical basic Pac. upperpart
colouration.
The question is- why is this bird so short winged? Is it
still moulting for some odd reason?