Friday, 16 October 2009

Wild Gull Chase

With the Azorean Yellow-legged gull continuing to be seen at Didcot most days I have had a couple of further attempts to see it. The nature of the location means that there are a large number of places the gull could be at any one time so finding it is tricky at best. For example, it could be on the tip rummaging through the rubbish, in which case one can't see it; it could be washing or resting on the level crossing pool (a good place to see it at close quarters); it could be loafing on any of the fields to the north of the B4016 (where distant views can be had); or it could be on any one of the private pits to the north nearer to Sutton Courtenay. In addition it is probably roosting at Farmoor each evening though it has only been seen there once so it may usually come in rather late. With so many choices and with all the gulls being rather mobile its pot luck as to whether one can see it on any given visit. I heard recently that a top Oxon birder had to make four visits spending a long time each day in order finally to catch up with this rarity. I'd made my first attempt on Sunday where the lack of the Azorean and the persistent drizzle had been more than made up for by the presence of a Baltic gull for just half an hour. This bird hasn't been seen since so I was very lucky to see it.

Most days the Azorean has been reported, mostly early to mid afternoon so on Wednesday I thought that I would have another go at it. I arrived at around 3pm, coming along the B4016 so that I could look out for gull flocks in the fields. There was a rather small flock of about 50 birds in the field closest to the level crossing so I stopped and had a thorough scan. There was one bird which looked interesting but the bill was wrong (the Azorean has very distinctive head streaking and also a rather striking bill with a yellow tip, then a black smudge and a rather discoloured base). I thought that I would try the level crossing pit next and said hello to another birder who was arriving just as I left. Some thirty minutes later as I was on the pit a text came through from Bird Guides saying that the Azorean was on the field that I'd just left. I can only assume that the newly arrived birder hadn't been as careful in checking out the looky-likey gull that was in the field. Meanwhile at the pit I'd been told that a competent birder had identified a 4th winter caspian gull that had been there for some time. Some of the other birders there put me on to what they thought was the bird and I dutifully took some video footage which included a perfect wing flap so I got footage of the underwing. This would enable me to confirm the caspian identity when I got home. I must admit that whilst the bird did look rather striking compared to the other non lesser-black backed gulls it didn't scream caspian to me though I freely admit that the whole herring/yellow-legged/caspain issue still leaves me somewhat floundering. I am pretty confident picking out adult yellow-leggeds by their clean heads and dark mantles once all the other gulls have streaked heads and when there are lots of others to compare the colour against and I think that I can now pick out a first winter caspian but the other ages still cause a lot of puzzlement. I think that I just need to see a lot more of them so that I can get a handle on the jizz. Anyway, once I got home I sent the shot to Ian Lewington who immediately e-mailed back saying that it was a classic yellow-legged gull pattern! So much for the authority of the other birds but at least it means that they struggle with picking out Caspians as much as I do. I am determined to get to grips with these identification issues and intend to make more visits to Didcot in order further to hone my gull skills. Anyway, despite staying until nearly dark there was no sign of the Azorean gull and it was another miss for me.

A perfect underwing shot revealing a yellow-legged gull rather than a caspian!

For yellow-legged gull identification (taken from "Scottish Birds Records Committee criteria for identification of Yellowlegged Gull Larus michahellis"):

What should be noted involves the extent of black in the primaries with, for Yellow-legged Gull, much black from P10-6 (where P10 is the outer primary feather) and, crucially, a prominent thick sub-terminal black band in P5. The P10-5 primary feathers should show small apical white spots, with P10 having a subterminal white mirror, which is sometimes present in P9, although very much smaller. This wing pattern excludes the argentatus subspecies of Herring Gull and Herring/Lesser Black-backed hybrids, which show either much reduced black in the outer primaries because of larger white apical spots and mirrors, grey/white tongues, and/or no black or a weak band in P5, mostly restricted to the outer web.

All of this can be perfectly seen on the underwing shot above.

The next day I was intending to take a break from gull hunting and dutifully do a full day's work. However at around 4pm a message came on the pager saying that the Azorean was back on the level crossing pit. As I'd reached a reasonable stopping point with my work anyway I told my VLW that I was nipping out and promised to be back by 6pm for dinner. Some thirty minutes later I pulled up at the pit only to be told that the bird and also a first winter caspian had both left about ten minutes ago (it's that ten minute dip for me again!). I was remarkably philosophical about it and decided to head over to the fields to see if I could find it. Fortunately the gulls were loafing in the nearest field to the level crossing so I pulled in at a lay by and had a thorough scan but there was no sign of it. I therefore decided to return to the pit and was just getting out of the car to press the level crossing barrier button when a birder who was there scanning the same flock that I'd just been looking at piped up that the Azorean was there! I parked and set up as quickly as possible and indeed there it was. Puzzled that I'd missed it I was relived to be told that it had just at that minute flown in. I spent some time watching it and doing some digiscoped videoing though the light was poor and the bird was a long way away. However the key identification points could be made out even at that distance: the strongly head streaking was confined and well demarkated to make a sort of hood á lá black-headed gull though very dark grey in colour; there was no streaking on the breast at all and the streaking colour is far darker than on any of the other gulls; the mantle colour is a shade lighter than the graellsii lesser-black backed but darker than a michahellis yellow legged; the bill has a striking yellow tip, then a black smudge and a rather non-descript base; the bird is structurely rather large compared to the other lesser-black backed gulls.

A couple of rubbish videograb record shots. You can see the lighter mantle tone, the striking head streaking which is well demarkated, the large size and the interesting bill pattern.

The bird ended up staying until 5:45pm apparently though I had to leave at half past in order to get back in time for dinner as promised.

I was most pleased finally to have caught up with this rare gull. Like the other two rare sub-species this year (American Black Tern and Baltic Gull) there is the possibility of a split in the future and it's a genuine mega for the country with only one other record (Martin Elliott's bird at Sennen in Cornwall) in Britain though there have been a few in Ireland.

No official BOU ticks for the year lists but there are now three rare sub-species which ought to be acknowledged:

Sub-species List
American Black Tern (Chlidonias niger surinamensis )
Baltic Gull (larus fuscus fuscus)
Azorean Yellow-legged Gull (larus michahellis atlantis)

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