Friday, 20 April 2007

Not So Solitary After All?

A lot has been said before and one must hurry to get things online before boredom strikes but that publication on DNA-based research into North American cryptic species really is remarkable and very inspiring.
One of the most surprising findings - at least in my opinion, heck, I always knew there was no such thing as a "Cinnamon Teal" - was that the two forms of the Solitary Sandpiper probably require being regarded as separate species. So far so good and nothing new anymore.
But what might strike us more than that is the fact that the vast majority of birdwatchers will very likely have to remove the Solitary Sandpiper from their life list, me included, because I am sure not many will have ever tackled the subspecific identification of the "species".

Gasp!

Let us be honest: as long as we don't know how to differentiate between the two species most of us won't have an armchair tick but indeed one species less on our list!
Surely I have seen it on a number of occasions in May 2005, actually I encountered a total of 8 birds on three occasions and they most probably (mostly) belonged to the nominate subspecies, but can I be sure? Do I know anything about the occurrence of the north-western subspecies in southern Ontario or Michigan?

No.

Even if it is unlikely, all could have possibly been western birds. And who knows, even if one has seen a multitude of Solitaries in California, they may all have been Eastern nominate birds. We just cannot know.

Oh, disgusting, a lack of knowledge! Ew, we can't have that and better get prepared for this spring's Solitary Sandpiper migration.
I recently ventured out into the world wide web and my local bookstore (Why buy them when you can look things up there and the store's just across the street?) to get informed. And if you are interested in putting the Solitary Sandpiper back on your life list where it belongs, you might want to read on a little more...


Names, Geography and Status
There are two forms, very likely separate species, as I have written before:

Tringa (solitaria) solitaria - from now on Eastern
Breeds in the south from central British Columbia all the way to Labrador.
This is the common form migrating through the East.

Tringa (solitaria) cinnamomea - from now on Western
Breeds to the North of solitaria, from Hudson Bay all the way to Alaska.
This is the common form migrating through the West. "Common" however needs to be put into context: the population of this western form is estimated at comprising only around 4,000 birds, making it one of the rarest North American shorebird forms, and it is in decline.
Now, that's scary. If however we take into account that the population of both forms put together is only around 25,000 birds (although the quality of the estimates is said to be poor), then roughly 1 out of 5 Solitaries is a Western and if they were equally distributed during migration, I'd have likely seen 1.28 Western and 6.72 Eastern birds - statistically. Well, "It's my list" but I am reluctant to put both forms on my life list, honestly. The trick for me is to not update my list until I have found both forms in southern Michigan this spring and then it won't matter, so now to the ...

Identification
Who am I to write about their identification?
Exactly: nobody!
I have only seen 8 birds ever and didn't even know back then there are two subspecies. What follows therefore is no authoritative essay on their identification, it is based on no expertise at all, it is only based on looking at as many images as I could find and trying to spot the differences. If you know better / more / whatever or want to contribute pictures, please leave a comment which I may use to improve these very humble lines! Highly appreciated.

Images I used
Here is a list of the images I was able to find on the Internet. Those bird images from the West Coast were attributed by me to show Western Solitary Sandpipers, those from East of the Rockies to be of Eastern Solitary Sandpipers.
That of course is something - yet again - which I do not know (most birds photographed in the West could also be Eastern birds while a few in the East could be Western), but hey, I had to try and sort things out somehow!

Western Solitary - spring
California April, Oregon April, British Columbia May (breeding Eastern?), Alaska Breeding Season, Washington May (use the "previous" and "next" buttons to see more pics of the bird), Alaska June, Alaska Breeding Season

Western Solitary - fall/autumn
California September, California August (both may indeed be Eastern)

Eastern Solitary - spring
Ohio May, Minnesota May, Ohio May, Ohio May, Ohio April, Kentucky April, New Jersey May

Eastern solitary - fall/autumn
Virginia July, Virginia September, Indiana August, Indiana October, Ohio July, Ohio July, Ohio September, New York September, New Jersey October, New Jersey August, Ohio July

In Between (central States, probably Eastern)
Utah August, Colorado April

Unknown Date and/or Place (probably mostly Eastern with one likely Western)
Link, link, link, link, link, link, link, link, link, link, link


Gathering these links was a lot of rather boring work, so please take a minute to appreciate it.

Thank You.


Possible Ways of Telling Them Apart

General impression - the "Gestalt"
Judging from the images, Western is a more slender bird with proportions reminiscent of a Lesser Yellowlegs (vaguely) whereas Eastern is a more chubby thing to watch and doesn't manage to conjure any resemblance to a Lesser Yellowlegs. The following might be of limited use to American birders, but from a Eurasian perspective, Western is more like Wood Sandpiper whereas Eastern is reminiscent of Green Sandpiper.
Furthermore, the bill of Western appears to be relatively longer and slightly more down curved, although this might also only be an impression and maybe not true when looking at absolute measurements.

Bill and Leg Colouration
Again, this is only an impression I have looking at the photographs and this is particularly difficult to judge, but it appears the legs of Western are brighter yellow than those of Eastern which shows a bit of a greenish shade to the legs.
Furthermore, the bill of Western appears to be quite prominently bi-coloured, with a pale basal two-thirds and a black distal third. This is also the case in Eastern, but the border between the two is apparently not as clearly defined as in Western and it seems to be a gradual change from pale to dark.

Plumage
In general, Western is a paler brown bird whereas Eastern is rather dark, appearing almost blackish when standing in the shade. This of course will be very difficult to assess on solitary Solitaries (guess you've been waiting for this to come up?) or birds in bright sunlight.
The tertials are often quite worn but when seen clearly seem to provide one of the two most stable and useful clues: both show a string of white spots along the edge of each tertial, but these spots are flat and rather rectangular in Western and look like the teeth of a saw (is that the correct English term for it, sawtooth?) in Eastern.
Another apparently very useful feature is the patterning of the lores: Western shows a very uniformly patterned, greyish head with a darker cap. Eastern however shows a blackish lore, connecting the eye to the bill, and a prominent white stripe above it and - less clearly defined - also below.

It seems that these features are valid - if indeed they are valid at all - for all age classes of both forms and can be used both in spring and fall / autumn.


What to look for - a short summary
So, when you are confronted with a Solitary Sandpiper and you actually care to find out which form it is you're looking at, focus on the following:

Proportions: slim and long or chubby and short
Bill length and form: long and drooping or not-so-long and more straight
Bare part colouration: bright yellow(ish) with a clearly bi-coloured bill or less bright and more uniform
Colouration of the lores: uniformly patterned like the rest of the head or with black-and-white stripes
Pattern of the tertials: row of rectangular, slim lines along the edge or triangular "saw teeth"

That's as far as I'll venture and I will leave the rest to the experts. Surely there are other and possibly more secure ways of telling them apart, maybe voice or primary/wing projection or whatever. But that's not for me to write about, that's best left to those with field experience and first-hand knowledge.

But for the time being, that's what I will go for here in Michigan this spring, so

bring on the Solitaries!

5 comments:

John L. Trapp said...

Interesting speculation, Jochem, but I'm not holding my breath that either the AOU or ABA will be recognizing this split any time in the near future.

Jochen said...

I know, I know...
My approach is that I always try to distiguish as far "down" the taxonomic ladder as possible and call them "forms", independently of their taxonomic status or official recognition. After all, I am from Europe and had to endure the gull torture of split after split after split where you never knew for many years what to do and think.
So I tried to avoid this in going for subspecies or "forms" where ever possible. If they get split in the future, fine.
If not, then I just had a reason to thoroughly learn and study the variation of "my" birds.
That's as far as I go and I probably won't "identify" the two forms of Solitaries, I'll probably refer to them as "Solitary showing field characters of ..."

But the most important thing: I think I'll be really enjoying this!

Patrick Belardo said...

Jochen,

Wow! You've upped the ante to the extreme. Thanks for putting in all this work. It's an article worthy of "Birding" or any other publication. I read an article in "Birding" last year about separating dowitchers. An interesting field mark that they looked at was the angle from the base of the bill to the eye. I haven't looked at all of those pictures you found side-by-side to see if maybe these 2 forms exhibit a difference in that structure. You may have already looked at that as well. Very thorough!

Larry said...

Very informative-A little over my head at this point, but I will keep an eye on your blog as I gain more field experience.

Jochen said...

Hi Patrick,
well, thank you very much but it's far from being that good.
What I did is present a hypothesis on how to separate the forms. I don't even know if this all is true and works out in the field or not.
But maybe people will think - like I do - thatthis might make some sense and test these criteria in the field, preferably where we know only one form is to be expected, like at staging sites in Newfoundland or southern Alaska.

Hi Larry,
just go for it, nothing's bound to stay over one's head for long as soon as one starts to tackle these problems. But as I said to Patrick, these are just ideas that were presented in hopes that people out in the field would test them.

Happy spring migration!