Earlier today, I found an interesting Dunlin at Pine Point, at the mouth of Scarborough Marsh. It flew in from across the channel on the incoming tide, and landed up Jones Creek, a couple of hundred feet away.
It was an adult bird, including an extensively black belly, and it appeared pale above and rather small. I needed a better look, but as I waited for the bird to slowly come closer, I posted to the Maine-birds listserve of a “…pale-backed Greenland (or other European-type)-like Dunlin,” mostly to alert other birders in the area (there were quite a few today as usual here). Based on the fact that this bird looked small, pale, and had not yet undergone molt, my mind immediately went to one of the “European” subspecies.
The bird had come considerably closer by the time Noah Gibb and Leon Mooney arrived, and it was clear that this was not a short-billed bird, perhaps on its own eliminating the Greenland subspecies arctica (one fitting this description was photographed this summer at Popham). But I will admit to not knowing the full range of variation in bill length among all of the 10 subspecies of Dunlin, so we went to work photographing and studying the bird.
We agreed that the bird appeared small (although the three other “typical” juvenile Dunlin that were present were never seen nearby, a comparison that would have been most helpful) and “not short-billed.” It wasn’t the longest, droopiest billed Dunlin that we’ve seen, but well within the range of our typical migrant subspecies, hudsonia.
As the bird came closer, plumage details and patterns blurred by heat shimmer and scope-shake in the 20+mph winds at a distance became more discernable. Arctica, the smallest and shortest-billed subspecies, also has a small belly patch. I don’t think this bird would be characterized as being short-billed or with a small belly patch.
Meanwhile, in response to my Maine-birds post, Louis Bevier chimed in that the subspecies arcticola which breeds in northwestern Canada and Alaska “is somewhat paler-backed than our typical hudsonia and delays molt until after migration.” That was not something I had remembered, but it’s been a while since I’ve done much reading on the subject. However, The Shorebird Guide by Michael O’Brien, Richard Crossley, and Kevin Karlson – which I grabbed as soon as I returned to the store – references arcticola as molting on the breeding grounds, as does our typical hudsonia. Bevier also stated that it is from “northern Alaska and the West Coast,” but that, I believe is actually referring to pacifica, which also molts on the breeding grounds (Arcticola winters in Japan, Korea, and China).
The Shorebird Guide cautions that “a few individuals of pacifica, arcticola, and hudsonia migrate before molting extensively.” While I could not see any signs of molt on the wings, back, scapulars, etc on this bird, of course some birds don’t always molt according to the book. Injuries (none obvious) or malnutrition (harder to decipher in the field) could delay molt, and some individuals can suspend molt for similar reasons – and others, such as simply being “screwed up!”
The only other reference I have handy here at the store is Richard Chandler’s Shorebirds of North America, Europe, and Asia which offers a similar array of caveats about subspecific identification. While saying “identification to race may be possible in favorable circumstances, most readily in breeding plumage,” it then goes on to warn that “At the end of the breeding season, separation will often be difficult, as feather wear renders the distinctions less obvious and upperparts become dull and blackish.”
It’s late September, and therefore it’s well past the end of the breeding season, making feather wear a serious issue. While I couldn’t see anything that suggested extreme wear (like on the flight feathers of a retarded 1st summer bird), there’s no doubt that any colors we were seeing were likely paler, and perhaps considerably so, than what the bird would be in fresh plumage.
Chandler takes the time to reason that “It is not easy to identify any of the races of Dunlin in breeding plumage away from the breeding grounds…Since races are established largely on the basis of the average characters of specimens taken on the breeding grounds, variation between individuals and differences between sexes, as well as variation with time owing to fading and wear as the season progresses, result in caution being needed when attempting to assign race to any particular individual. Consequently, there will always be more than an element of speculation with the racial identification of many migrant Dunlins in breeding plumage.”
So where does that leave me with subspecific identification? Completely and utterly unsure.
Is this simply a hudsonia that has not molted yet for some odd reason? Maybe. Is this an arctica, like my first impression? I don’t think so anymore (too long-billed and with too much black on the belly). The only thing that is definitive is that this is an interesting and educational bird. Hopefully, it will be seen again, and perhaps better photos – and photos with “normal” Dunlin – could be acquired. But for now, I am fine with saying “I don’t know.”
I present an array of phone-scoped images for you to ponder (or not). I’ll also send this link out to those who know more about Dunlin subspecies than I do. It’s going to be a busy two weeks for me (Birds on Tap!, Monhegan tour, than travel to a trade show), so I may not get back to an analysis of the analysis for some time, but if anything revelatory becomes apparent, I’ll discuss that here.
9/23 UPDATE: Jeannette and I observed the bird again yesterday, 9/22 and Jeannette took excellent photos, as usual. It was also a whole lot closer, allowing for much more detailed study. You can ignore those awful photos above, this is what the bird really looked like!
So, the next session with the bird shows several pertinent details:
1) This bird IS in molt, as several new coverts and tertials are visible.
2) The outermost primaries (especially as you can see in flight) ARE indeed very heavily worn (it could be a 1st summer/2nd winter bird afterall?).
3) The size and structure looks more than fine for our typical subspecies, hudsonia.
Those, combined with the details of the plumage, show that this is undoubtedly NOT a European bird. Instead, it is either one of the North American subspecies in very retarded molt (or perhaps a vagrant East Asian bird). I’ll synthesis what I learn when I return in a couple of weeks, but for now, I wanted to get these much more useful photos posted for you to ponder, enjoy, and/or ignore.
Regarding arcticola, I was on the road and thinking about possible strays. I had noted to the Maine email group earlier this year that:
The North American, Pacific, and east Asian populations of Dunlin molt on the breeding grounds or at molt migration stopovers far to our north.
So I knew this about arcticola. I made a mistake while in a hurry but had recalled a difference in molt timing between pacifica and arcticola that might be relevant. As posted to the Maine list, pacifica takes longer to molt (it breeds south of arcticola in western Alaska with a somewhat longer summertime; see Holmes 1971, Condor 73: 93-99). But both pacifica and arcticola molt on the breeding grounds.
Other key references on subspecies worth checking are:
Browning, M. Ralph. 1977. Geographic variation in Dunlins, Calidris alpina, of North America. Canadian Field-Naturalist 91(4): 391-393.
Greenwood, Julian G. 1986. Geographical variation and taxonomy of the Dunlin Calidris alpina (L.). Bulletin of the British Ornithologists Club 106 (2): 43-56.