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.  

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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.

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References:

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.

 

Comments

[Rick Wright]

First. Rate. I'd expect nothing else from Catherine, but this is exceptionally fine.

[Nancy Magnusson]

Claudia Wilds told us in a class once that a particular asymmetric feather pattern at the base of the bill is indicative of a Baird's Sandpiper. The asymmetry of which she spoke is nicely shown in this photo I found on Flickr: http://www.flickr.com/photos/hudsonian-godwit/7827279632. Note: indicative only, to be used with other field marks.

[Nancy Magnusson]

To see the photo, you need to remove the '.' that was appended.

[Matt Brady]

Here's a Western Sandpiper that seems to show the gape notch: <http://www.flickr.com/photos/podoces/3487368821/>

A quick Google image search of Western Sandpiper turned up plenty examples of Western Sandpipers without the gape notch. The photo linked above is perhaps an atypical individual? Or maybe the lack of a gape notch definitely indicates a Western/Semi, but the presence doesn't necessarily indicate a stint?

[Doug Pratt]

Couldn't access either of the photos mentioned earlier. Need more info on where they are on the sites.

[Kelly Sekhon]

Corrected links to the two photos mentioned above

http://www.flickr.com/photos/hudsonian-godwit/7827279632

http://www.flickr.com/photos/podoces/3487368821/

[Ann Nightingale]

Fantastic observation, Catherine! I'll be using this from now on. Thanks, Nancy, for the tip on the Baird's, too.

[Tom Auer]

Here's a Little Stint from RI last summer with the gape notch. I'm guessing that the gape notch is like a number of other field marks, not 100% reliable at eliminating all other groups, but a very strong feature that will help pick out good Stint candidates and help add to the evidence.

http://ribird.org/galleries/2/pictures/51

[Steve Howell]

As in almost all field marks there will be exceptions, and being brave enough to post something online is a sure way to find them! I agree the Western Sandpiper referenced by Matt Brady does show a bold gape notch, but in my experience this is atypical, and maybe after watching the bird feed for a while this notch might be covered, as happens with albatrosses (cf. Chatham Albatrosses, on link at end of this message); or maybe not. Also on the link, for what they’re worth, are fairly typical examples of the relevant stints and peeps, mainly in the “impossible” nonbreeding plumages. Note some variation in the gape feathering, but the general pattern holds up. See http://www.flickr.com/photos/79546200@N07/sets/72157632695755639/

Steve Howell, Bolinas, CA

[Christian Artuso]

Interesting! Thank you! Although these features are already illustrated subtly in the Birds of Europe (even if not commented on in text)… looking through my own photos of these species, it seems this feature may not be completely reliable… certainly some / many Semipalmated Sandpipers show a gape notch as distinct as Red-necked Stint…

[Andy Kleinhesselink]

Here's a difficult basic plumage Little Stint from December in California--no Western's to compare it too unfortunately:

http://www.flickr.com/photos/22565054@N04/5601715531/in/set-72157626333503237/

Cool observation.

[Andy Kleinhesselink]

Oh just saw Steve Howell's post above--same Little Stint he shows from CA.

[Matt Brady]

I just checked out the dark-legged stints in the LSU Museum of Natural Sciences. Of the Semipalmated Sandpipers (n=76), 8, or just over 10%, had noticeable gape marks. The average for these birds was a gape mark extending 0.7mm past the bill (with a range of 0.3-1.2mm). Of the Western Sandpipers (n=116), only two (~1%) had gape marks, of 0.5 and 1.2mm. The Little Stints (n=7) and Red-necked Stint (n=1) are very old specimens, and the gape mark isn't very clear.

So, I'll definitely be looking for gape marks on dark-legged peeps I see this spring!

[Gunnar Engblom]

I will have to test this with wintering stints in Lima. Hoping to find a rare Little or Red-breasted Stint this way. Thanks for an excellent post, Catherine.

[Alfredo Begazo]

Sharp observation!

[Alan Contreras]

I just looked at the fall adult Red-necked Stint pics I took in Oregon in July and the "notch" feature is either not present or obscured by feathering or mud. The photos are not crisp and the bird definitely had some goo and wetness around the base of the bill that could affect what I'm seeing.

Alan Contreras
Eugene, Oregon

[Luke Tiller]

Hi Alan,

The notch seems to be pretty evident in the picture of yours that they used on the ABA blog even given a slightly strange angle and a not totally clear shot: http://blog.aba.org/2012/07/abarare-red-necked-stint-oregon.html

Luke Tiller

[Kevin Karlson]

While these are interesting observations, I would only use them as supportive features for a more comprehensive ID of similar stints/peeps. I looked at a few Little Stint shots of mine from Israel in 2010, and one bird showed a very tiny dark line behind the gape, and the other did not show any mark. These were nonbreeding adult birds in fresh plumage. With these micro field marks, a variety of factors can influence what you see in the field, especially displaced feathers and loral feathers that are wet or bunched together, but it seems that Catherine has opened a door for further study. It seems to be a good set of supportive features to prove over a period of time, and Catherine is such a fine artist and has such a good evaluative eye that I will test her hypothesis personally over time. Thanks Catherine and Luke for putting this information out there. Great accurate drawings of the stints and peeps as well, Catherine. Kevin Karlson

[Catherine Hamilton]

Thank you everyone for the excellent feedback thus far, both here and privately, from both sides of the pond. Thanks Matt for checking the LSU specimens - I checked at the AMNH and the NHM of LA Co., but it is really good to hear findings from other collections, especially considering the small sample sizes here for the stints.

I will be very interested to hear what people see in the field!

[warren harrington]

Hi Kevin, I was happy to now have your great book thankes to Ellie getting me the book for Valentine's day. Would love to have your signature to go in it. Thank you, Warren Harrington

[Luke Tiller]

Hey Kevin,

Thanks for the feedback. I thought I should probably point out that, though I'd like to, I can't take more credit for this article than simply reading the first draft.

All the best - Luke

[Russ Namitz]

Catherine~

Two friends of mine identified an unusual (presumed) summering Red-necked Stint in 2011 along the southern Oregon coast. It was thought to be in its 2nd year of life and a few skeptics were unconvinced as to its identity due to poor initial photographs. Better photos show a defined gape notch like you have illustrated. Nice to have additional, supportive features for tough identifications like this one.

https://picasaweb.google.com/113581614565937060167/OregonRareBirdsReviewSpecies#5844521382397246418

Sincerely,
Russ Namitz
Medford, OR

[Tom Stephenson]

Hi Catherine,

Someone just sent me a link to your interesting article. I'm not sure the notch is always missing from our "stints" but it seems like a point that needs more research for sure.

Here are a few pictures of stints from Asia along with some Long-toeds and a Least for comparison.

Best regards,
Tom

[Tom Stephenson]

Somehow the link to the photos didn't survive the comment.
Here it is again.

http://www.flickr.com/photos/93523467@N02/

Tom

[Andrew Baksh]

Very good article. I expected nothing less from you with that sharp eye of yours. This is an interesting theory and while this field mark may be highly variable among the small peeps, it is worth looking at; especially, as you pointed out toe field marks are often obscured. I will be sure to study this at length in the field and document my findings. Best always, Andrew.