Thayer's look alikes

My last post was of a Thayer's Gull in Tsu city, Mie prefecture. This is a quick follow-up showing a couple of interesting Vega Gulls with thayeri-type outer primaries that diverted my attention the following morning while failing miserably to relocate that Thayer's.


The first looked very like a Thayer's in flight, so much so that had I only seen it fly by I'd have been frantic to get further views. Fortunately I'd been able to scope it at fairly close range on the beach before it took flight and had already satisfied myself it was a Vega. A case of whether to go old school and (try to) get the ID straight first or go for photographs and try to sort it out later. I went for the former but I'd have preferred to get the shots as well.


At rest the large size and darker-than-Thayer's saddle didn't raise any red flags, it looked Vega through and through and the only reason it had originally attracted attention was because it showed more than usual white in the primary tips. Much as argentatus can compared to argenteus but such Vegas aren't aren't uncommon even if they are relatively few in number. When it flew the pattern matched Thayer's almost to a tee and that was more of a surprise; being whiter-winged is one thing but having a pattern close to Thayer's is fairly rare. Even the p5 sub-terminal band was very narrow (almost non-existent on the right wing) and that in itself is rare.

 

Though I was happy with my original Vega ID I wanted to see the bird again and hurried off down the beach to look for it. When I arrived in the general area I was further sidetracked by this second  candidate, admittedly a much less plausible one. Again, it had thayeri-type primaries but there was more extensive black towards the bases of the outermost primaries as well as a broader, very prominent sub-terminal band on p5.

Yesterdays Thayer's for comparison. Blackish-grey rather than black on the upper side of the primaries, an almost unmarked p5 and much paler underside which looked essentially white when the upperside pattern wasn't showing through as in this shot.

On the ground it looked very similar to the first bird in structure and the saddled colouration matched Vega. The deep purplish legs caught the eye but Vega can be equally dark-legged so I wasn't too worried about that. The primary markings looked solidly black.

With two Taimyr Gulls.

However the more I watched it the more I wondered if it might not be a hybrid of some description. I don't like to jump to the hybrid option for every odd gull I see but in this case there were other factors which didn't sit comfortably with Vega. It looked slightly truncated at times, perhaps a shade short in both primary projection and tail as well as deeper-bodied. These points weren't always apparent though and the most significant feature was a yellowish orbital ring.

In life the orbital ring seemed to have a very strong yellowish element but this doesn't show in any of my images. Nevertheless even in the heavily cropped image above there is at least a suggestion of orange that I haven't definitely seen in Vega which ranges from pale pink to deep, dull red. Glaucous Gull and the rare American Herring Gull are the only species here which have yellow orbital rings and it was this that got me thinking along hybrid lines. Not an F1 but with some degree of backcrossing. Below are a couple of typical Vega in the same flock with obviously red orbital rings for comparison; one still with winter streaking and the second with traces of winter worn away.

 

The final head below is the previous day's Thayer's still showing a hint of its former smudged head markings not yet totally worn and faded away.





And back to the bird in question again. As you can see from these shots, it's an interesting individual but no concrete evidence that it is a hybrid, particularly as the orbital rings don't look as yellow as I believed they were in the field leaves me thinking it may just be an odd Vega afterall.