Saturday 17 March 2018

Thayer's Gulls in Mie: Dread Pirate Roberts in Ise Bay

Thayer's Gull, or should I say the gull formerly know as Thayer's? Hardly less convenient than 'Iceland Gull of the subspecies thayeri', is it?. Nah, I'll stick with plain old Thayer's, it's only a matter of time till it's re-split. Yeah... well, back to reality.

There seems to be a local belief that there's only ever one Thayer's Gull in Mie; Mi-chan must now be in her eleventh winter on the same beach. I don't know how closely others look at Mi-chan but I've been increasingly doubtful about this. There is a high turnover of a certain percentage of the gulls on the beach while others remain very loyal to the same stretch of sand, you get to recognise quite a few of the more distinctive individuals. One problem may be that the annual Thayer's is quite loyal to the same spot on the beach year after year and it might be easy to jump to an erroneous conclusion.

The very obviously different gull this winter is loyal to the same spot Mi-chan was normally to be found at and this prompted me to look more critically at the Thayer's I've photographed over the past three winters. I can say with absolute certainty, after examining eye flecks and primary patterns, that not only is the Thayer's I'm seeing this winter a different individual to last winter's bird but that it in turn was different to the bird the preceding winter. Three winters... three different birds: Dread Pirate Roberts looms large.

In the past when I've mentioned seeing a different Thayer's to locals I've been told there are several hybrids around, the inference being I'm mistaken in my identifications. It's true there are both hybrids and 'white-winged' Vega but I suspect some people may not be looking carefully enough at any Thayer's they see and are simply assuming it's the returning bird.

Generally speaking Vega with thayeri wing patterns aren't too difficult to identify though they will always be a pitfall for the unwary. They tend to be typical Vega size, build, saddle shade and if you're lucky also pale-eyed. Hybrids can be trickier as they may come in a variety of guises but the obvious ones tend to suggest Glaucous or Glaucous-winged influence and match neither Vega nor Thayer's on closer inspection. More of that later.

Thayer's Gull 2015-16
No doubt when a Thayer's first returned to Tsu birders were looking more closely and I'm sure the first individual must have turned up on successive winters to create the Mi-chan legend. I was told categorically that this bird was Mi-chan so for arguments sake I'll assume that is the case.

The Thayer's I was told is Mi-chan 8 April 2016. I heavily cropped and lightened both sides of every gulls' head to bring out the flecking patterns of each eye before comparing the birds from successive winters. I won't post them here as they aren't of much interest beyond confirming the different patterns, plus space is limited.

This wasn't the greatest image to judge wing tip pattern from, however I got far better images in subsequent years and this was good enough for comparison.

Thayer's Gull 2016-17
I saw this bird many times between early February and late March.

February 11

March 15

March 23

March 15

March 15

Thayer's Gull 2017-18
This is the most strikingly different bird, lacking melanin on p5 bringing it within argument distance of Kumlien's Gull. Add to that the p9 mirror breaks through the outer web on one wing (not quite on the other) and there's a strong contrast between the outer and inner webs on p9-10 make this is an interesting gull. This is either a pale end Thayer's or a dark end Kumlien's... but hey, post-lumping I don't need to lose sleep over this, right? Hmmm. One thing is for sure, no one should mistake this gull for previous Mi-chan incarnations.

In flight there's a strong contrast between the inner and outer webs of p9-10. The right wing has a small notch on p5 but this is concolourous with the rest of the upperwing, there's no corresponding notch on the left wing.

The left wing p9 mirror breaks through the leading edge...

...on the right wing it doesn't.

The inner webs of p9-10 are significantly paler than the outer webs. The concolourous notch on p5 is easily seen here.

No notch present on p5 of the left wing.

It can look either small-headed and -billed or not, depending on the view.

The eye is also within Thayer's range but is at the lighter end of the scale. I suspect this would no more be seen as a Thayer's in Newfoundland as it would a Kumlien's on the west coast. In Japan? Well, a pale-end Thayer's is far more likely but generic Iceland Gull does just fine. 

So there we are; three Iceland Gulls in three winters. But what about this next bird?

After seeing the previous bird intermittently throughout the day, earlier this week, I was stopped in my tracks by this next gull. Is this another Thayer's? I'm sure it can't be a 'white-winged' Vega, of which there are quite a few, too many features are 'off' for Vega. I feel it can only be a hybrid if not Thayer's but Glaucous x Vega hybrids are always rather large and adult plumage doesn't closely mimic Thayer's. The potentially more similar Glaucous-winged x Vega should also look larger and broader-winged. Either way neither cleanly tick as many Thayer's boxes as this bird and I confess I'm stumped.

This gull really stood out at the back of the flock; very small, very pale-saddled and with a full winter cowl at a time other gulls are largely white-headed.

It continued to keep my full attention as it moved closer, a delicate bird with a nicely rounded head and smallish bill.

The rather short, purplish legs don't detract from the overall impression of Thayer's, it even has panda patches round the eyes.

It has a dark medial band on p10, not a problem for Thayer's.

It moved back towards the shoreline and this was the only sharp shot of the spread wing I was able to get in the deteriorating late afternoon light. The outer primaries are still within the Thayer's range but...

...what's going on with the underside of the primaries? In the field I couldn't see any detail but was struck by how extensive the dark grey of the outer primaries seemed.

This image came as a shock when I saw it. A medial band is one thing but surely the underside of p10 can't be this extensively dark. Or is this an impression created by the underlying p9? A medial band on p9 isn't a problem either, particularly if it's a young adult, but that broad? And what exactly is that dark line that appears to run along the trailing edge of p9? If it is a p9 feature then any notion of Thayer's must be dead but could that also be caused by the underlying leading edge of p8. For such a strong candidate in the initial stages, these underwing views are very surprising. Surprising and confusing as I struggle to think of a progenitor pairing that could produce such a small and delicate pale-saddled gull like this, unless one of the parents was a dark-winged Iceland Gull. 

I mentioned earlier I'd come back to the 'white-winged' Vega angle. So briefly, I hear a lot about hybrids in Mie but I believe many gulls that might be confused for Thayer's at first glance are in fact actually Vega rather than hybrids. The following gull is Vega as may be the subsequent bird, I don't think there's any need to go down the hybrid route. 

The primary pattern is good for Thayer's but the birds like this always show black colouration rather than blackish-grey.

The same Vega showing the underside of the primaries.

At rest the typical Vega structure is apparent. I don't have a direct comparison shot but this bird was large and with the same saddle colour as other Vega present.

A heavily cropped image shows it not only has a pale eye but a pinkish-red orbital ring.

This next bird may have mixed genes in its ancestry or it may be pure Vega even if it is slightly paler-saddled. Naturally backcrosses will further complicate matters.

A plausible Thayer's wing tip.

An eye-catching far wing and a marginally pale saddle for Vega. Again I'd settle for Vega rather than going down the hybrid route but there is room for slight doubt.

No comments:

Post a Comment