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Wednesday, February 2, 2011

Gull Debate and Year List Check-In

Mark Lewis, co-author of Birding in the San Juan Islands, left a comment on my recent Whidbey Island blog post questioning the ID of the gull in the photo I posted. I identified this gull as a western gull, but he suggested it might be a Thayer's gull:

After closer examination and a little research, I'm still doubtful it is a Thayer's gull for the following reasons: A) The bill does not show a two-tone greenish tinge, B) the legs are not a deep pink, C) the head shape is more flat than rounded, and D) the underside of the far primary is not pure white (see Greg Gillson's discussion here). However, I'm now wondering if it couldn't be a herring gull? Or a glaucous x western hybrid? Your input encouraged.

Is anyone else starting to think that maybe most or all of the Larus gulls should be considered one species? Once I'm getting into reading about all these hybrids and back-crossings, I've got to wonder.

Regardless of the final conclusion on this gull's identity, I for the time being am going to keep it #114 on the year list. Thus I closed out January with 114 birds on the year list, 14 species above my goal and a whopping 27 species above last year's January total.

The only other bird I've added since then is this greater yellowlegs (15) I saw at Jackson Beach yesterday:

I also went for a walk at British Camp today, but was unable to find the varied thrush that has eluded me thus far this year.

Next up, a couple more marine science notes of interest, plus a report back after checking in with some other gull references.


Dave Wenning said...

How exactly are gull species determined? Does individual variation come into play to any extent? In my own lifetime, the Rufous-sided Towhee became two species, with and without spots. We humans, Juncos and domestic dogs each are only one species with a lot of variation in sizes, shapes and colors. Could this not also be the case with gulls?

Rainsong said...

One hundred and fourteen! Even pre-Rudy (our Rat Terrier) days we did not get that many and we looked with purpose at our mountain valley home and made side trips to places like San Juan where, by the way, there were always spotted towhees and varied thrush in the tangle of trees starboard of the picnic lawn with the big down trees. We would count the amazing number of Robins and suddenly notice that one or two, not hanging with the rest, were something else. Even when we only stopped for lunch instead of overnight we would find them if we sat still long enough. Good hunting Monica.

Warren Baker said...

Poor old Dave will be pulling his hair out trying to catch you Monika :-)

He loves Gulls, maybe he'll answer your conundrum!

Mark - Birding in the San Juan Islands said...

The other commenter posed some great questions about what exactly defines a species. In my excitable youth I was a proponent of splitting species as it was so much fun to have new species to chase! In my maturity I have thrown my lot in with the lumpers as it makes more "biological sense". Individual variation within gull species is very high, especially in the immature plumages as pointed out in Dennis Paulson's most recent Slater Museum blog entry. And then you have extensive hybridization in coastal species where their ranges abut, resulting in a complete lack of phenotypic cohesion. (Haven't those silly birds ever heard of the venerable "biological species concept"?) I think we should call all the gulls that freely hybridize on the eastern side of the North Pacific the "Eastern Pacific Gull" and do the same with the group of large coastal larids that breed and hybridize along the Arctic Ocean, too. It would solve a lot of "problems", but then we wouldn't have as many opportunities for these fun debates!

Monika said...

Dave - Good question! Perhaps the fodder for another post.

Rainsong - For some reason those varied thrushes haven't been in their usual spots! Ah well, just 116 waiting to happen.

Warren - Dave's got me started on these gulls now....

Mark - You're right about it being a great conversation starter! I heard back from Greg Gillson, who I've learned about birding from, and he suggests this is in fact a western gull due to the school bus yellow bill, the speckled with dark eye, and the yellow-orange eye ring. Do you agree?

Lancashire and Lakeland Outback Adventure Wildlife Safaris said...

Couldn't see it on my monitor and was going to ask if you could see it on the original but GG has beaten me to the orbital ring colour.

Keep those Larid conundrums coming...



Lancashire and Lakeland Outback Adventure Wildlife Safaris said...

To answer Dave on Fidalgo's question
How exactly are gull species determined?
I don't think the gulls themselves know the answer to that one!!! Be interesting to see if our Lesser Black Backs L.f.graellsii produce fertile offsping with your Am Herrings L.smiths when they get there in guess is that they will thus closing the 'ring'



Mark - Birding in the San Juan Islands said...

To be honest, I'm just "shooting from the hip" when attempting to ID a difficult gull from a compressed image. My original take was based on GISS/jizz and feather coloration. But the subtleties I mentioned such as head shape and bill proportions can look markedly different with a slight change of viewing angle, lighting, or feather erection. Your bird does have a startlingly clean head & breast for mid-winter and that is a good trait of Westerns. I simply can't see the iris or eye-ring and the bill color is different depending on which monitor I use to study it.

Monika said...

Greg had the advantage of me e-mailing him a higher resolution version of the photo - that's how he was able to determine the eye and orbital ring color. Even with a great photo in ideal conditions it can be difficult to tell these Larids apart!