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All:
Here's a copy of a note I sent to the advanced i.d. site at birdwg01, Tricky
business, but I feel that it was indeed a Common Ringed Plover.
It is good that Dave Brown gave access to the image of an interesting small
plover photographed [by Nicolass Honig] Sept. 4 near Halifax, Nova Scotia. It
came to my attention after Allan and Cathy Murrant saw the photo and pointed
out features of Common Ringed (CORP) rather than Semipalmated Plover (SEPL) -
lack of visible orbital ring and broad breast band. They also posted the image,
along with great shots of a Eurasian Whimbrel in Sydney, NS, in early Sept.
<http://www.capebretonbirds.ca/rarebird.html>
With Dave Brown, I have been agonizing over it since, and both of us are puzzled
by the lack of response on this forum. Is it considered too obviously one
species or the other? I have checked numerous images, particular from Google
and Vireo, of fall-migrant adults (July-November) and they sure address some
views on distinctions.
1. Widths, shapes and sizes of breast band and all dark head patches on both
species vary individually, and highly with posture (a warning in some sources).
Few SEPL show as evenly broad breast band when expanded as the NS bird. Few
CRPL have a strongly convex lower border of the auricular patch, and rarely so
far back as on the NS bird, but some do(depending on posture?), whereas most
SEPL have this shape.
2. White patches are quite variable. The white frons can extend to the eye in
both species, or there can be a dark intervening area. One nice image from
Iceland shows a July adult with a very broad dark area between white frons and
eye. Shape and extent of the white supercilium also varies greatly in both
species, and behind the eye can extend below the upper border of the eye in
both, though more so in some SEPL.
3. True length and height of bill (see Pyle's Id Guide . . . on this) are of
little use, but SEPL almost always shows a slight "dip" in the culmen,
imparting its oft-mentioned slightly bulbous tip. The CRPL culmen seems always
straight until near the tip, making it seem longer and thinner (head on images
seem to show the CRPL bil as more sharply pointed). The NS bird seems good on
bill shape for CRPL.
4. The tone of back and wing plumage of most (but not all) CRPL is distinctly
paler and grayer, but a few SEPL can be quite grayish. There is some
possibility of confusion here from the use in photo guides of images of darker,
browner _tundrae_ from Eurasia and AK. The expected _hiaticula_ from Greenland
and Nunavut is sometimes separated as a browner subspecies, but that's also
said to be dubious. The NS bird is a little problematic, as its back is
strongly shaded amd its wings and flanks obliquely lit. But, a zoom of the
image shows a distinct paler gray cast to the better-lit scaps and coverts
6. The pale orbital ring (distinctly yellow in fall-migrating adults) of SEPL
is a most salient feature, surely, and is clear on all decently sharp images,
even when ill-lit. The dark brownish or dark brownish orange orbital ring of
CRPL is obscure at best and completely invisible on most well-lit CRPL images.
The light on the BNS bird is oblique on the head, but it is sharp, and zooming
reveals no hint of pale orbital ring, especially at the reasonably well-lit
front of the eye
Finally, although CRPL and SEPL are rated as good species, and although Smith
(Ibis, 1969, 111: 177-188) made some dubious observations on mixed pairs
producing Mendelian ratios of morphology of each species, interbreeding may
indeed occur in n. Nunavut (especially with global warming?). How would one
pick out a hybrid?
Cheers, Ian McLaren
Ian A. McLaren
Biology Department
Dalhousie University
Halifax, NS Canada B3H 4J1
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