Open Mic: A New Field Mark for Differentiating Stints and Peeps
At the Mic: Catherine Hamilton
Artist Catherine Hamilton, of New York, NY, holds a Bachelor of Fine Arts from the Rhode Island School of Design and a Master of Fine Arts from Bennington College, but is currently, as usual, walking a bit off the beaten path. Her drawings and observations can be found at her blog, Birdspot.
As an artist and a birder, I can’t seem to get enough suffering from studying gulls and sparrows, so over the past few years I have spent some effort in learning to draw shorebirds. Assessing proportion or pattern in a manner that involves the eye and hand simultaneously can give people who draw a unique perspective on avian identification, whether through field sketches, specimen studies or in using photographic references. Reviewing photographs is a tricky arena - its parameters and pitfalls are outside of this article, but I want to point out that photographic limitations can provoke discovery as well as heated arguments.
I was once emailed a photo of a lone shorebird, puffed out against the cold, the photograph weirdly exposed and the bird itself in a particularly drab basic plumage. Bill shape and proportions were hard to assess, scale and size were impossible. The bird was a Sanderling - this one should have been easy, no? Not to the beginning birder who posted it, and not even to others, who ranged through various Calidris IDs. I wrote him, explaining why, even though its shape looked all wrong, it was in fact a Sanderling (heart racing and hoping fervently that I wasn’t wrong!). My identification points ended with a simple “Even if all other characteristics look off or muddled, you can always spot a Sanderling in a photo because of its gape notch. Semipalmated and Western Sandpipers really don’t show that.”
I discovered this Sanderling “gape notch” from drawing them, and wrote about it in a blog post in 2010. I then went on to look at other Calidris sandpipers in the field, in museum specimens, and in thousands of photographs, and what I found startled me. Amongst the small peeps, there are noticeable differences in the feathering around the gape, most notably between the black-legged Old World stints and our black-legged New World peeps.
I have illustrated the differences here. Little Stint and Red-necked Stint typically show a well-defined gape notch:
Whereas Semipalmated and Western Sandpipers do not:
In the field, it might be useful to look for this, since the determining field mark of toe semipalmation in Western and Semipalmated Sandpipers is often frustratingly obscured by mud or water. I was delighted to see this feature while observing the Little Stint at Piute Ponds in July of 2011.
Plumage differences have been thoroughly described (Veit, Jonsson, 1987), but also referred to as being so difficult in nonbreeding plumage that identifications are often wisely left hanging, or that only breeding adults are easily identified (Sibley, 2000). Bill variation is great enough among these species that bill structure has been stated as insufficient to establish an ID alone (Veit, Jonsson, 1987). Given these difficulties, and given the desirability of finding vagrant stints in North America, it would be nice to have another point of reference to clinch an ID. Individual variation exists, birds might look a bit different if they are molting feathers at the gape, and this is based upon a closed bill, but even with these caveats the gape notch can be quite striking and is worth looking for on a suspected stint.
As a side note, the gape feathering on Least Sandpipers (not illustrated here) is also different from Little and Red-necked Stints, but less markedly so: Least Sandpipers show a slightly different notch, but since the feathering in this area is likely variable, I am not sure I would rely on it while in the field. It does not seem that it will help with the conundrums of identifying a Least Sandpiper from a Long-toed Stint, for example. The differences in the gapes of Western and Semipalmated Sandpipers are more clearly evident.
I would love to hear from other birders with more Calidris experience than I, especially if you have reference photos. I have discussed this with some notable authors and birders, and it appears to hold up. The gape notch is evident on both breeding, non-breeding, and juvenile plumages. In fact, look for a prominent upcoming book with this feature in it - I have been told that plates were changed to reflect this!
Thanks to Steve Howell for encouraging me to write up this observation and to Kimball Garrett for access to the Museum of Natural History of Los Angeles specimens and for pulling out a number of extra fresh and pickled specimens to help out. Many thanks to Luke Tiller for reviewing this article.
Veit, R. R., and Jonsson, L. (1987). Field Identification of Smaller Sandpipers within the Genus Calidris. American Birds, 41(2), 213-236.
O’Brien, M., Crossley, R., & Karlson, K. (2006). The Shorebird Guide. New York, NY: Houghton Mifflin Company.
Jonsson, L. (1992). Birds of Europe. London, England: Christopher Helm, A & C Black Publishers, Ltd.
Sibley, D. A. (2000). The Sibley Guide to Birds. New York, NY: Alfred A. Knopf, Inc.