Tuesday, 12 October 2021

Hello Portland. It's Been a While...

The last time I went birding on Portland was 3rd May 2004, when two adult Long-tailed Skuas and a dark-phase Pom were the stand-out highlights. So why the 17-year wait? I've written previously about my tendency to go there almost never, and it is something I've been meaning to rectify since publishing that post. And finally, nine months later, I have...

My last October visit was almost exactly 25 years ago. I referred to that day in the post linked above, and remembered to mention the several Firecrests, the Lapland Bunting and the unwelcome lack of Northern Waterthrush. But I had completely forgotten about the smart male Subalpine Warbler in the Obs quarry! Even my Portland dips are nicely decorated.

Today was not a twitch though. Just a straightforward on-spec visit, with no expectations beyond a nice walk and dry weather. The Portland Bird Observatory terrace at 06:30 was a fine spot to watch the sun rise and begin the day's caffeine-loading. In the half-light a distant, idling diesel engine was briefly misidentified as a churring Nightjar. It could only get better...

At first light there were birds everywhere, especially at the Bill. Loads of Pied Wags, Meadow Pipits, Linnets etc. A Golden Plover went over at the head of a Woodpigeon flock. Lots to look at. As the morning progressed, the sun rose higher and grew hotter. The afternoon was absolutely gorgeous, though unsurprisingly not that birdy. Some pics etc...

At 09:15 I accidentally flushed a Short-eared Owl from some stubble right next to the track I was on. It plonked down further away, and I could see its eyes peering at me and its stubby little 'ears'. Unfortunately this Crow was on it straight away, and chivvied it into the air...

Short-eared Owl getting grief

I didn't get a photo of the Golden Plover, but I did get this...


I had my recorder switched on for the duration, but sadly didn't capture anything else to get excited about. Not that I'm aware of anyway. Mind you, there was certainly some potential around. Like this, for example...

Bird of the day for me - Yellow-browed Warbler

Seeing Yellow-browed Warbler in the hand was a personal first, and the result of a beautifully timed coffee break. Just wonderful.

During the afternoon sunsine there was plenty of non-birdy stuff on the wing, and occasionally settling...

Comma

Migrant Hawker

Unfortunately the three Clouded Yellows I saw failed to cooperate, but were definitely the best of the inverts. For what it's worth, my bird tally: 20 Chiffs (undoubtedly a huge undercount), 8 Blackcaps, singles of Whitethroat, Yellow-browed Warbler, Golden Plover, Heron and Wheatear. Needless to say, there were thousands of other birds, and so there should be in about 12 miles of walking! Talking of Wheatear, I almost forgot...

Obviously there's a Wheatear photo

Finally, it was great to chat briefly with fellow Dorset birder Joe Stockwell and PBO warden Martin Cade. I thoroughly enjoyed the change of scenery and look forward to visiting again, and maybe next time I'll ponce a cup of Obs tea to go with my choc-chip muffin...

Monday, 11 October 2021

No Siskins

Yesterday was glorious again. A sunny afternoon plod round Cogden and West Bex was predictably lacking in birdy thrills, but 2 Whinchats were nice to see, and 4 Clouded Yellows. Actually, it was really a day for butterflies. And dewy bottles of beer.

This morning I made an effort. Out reasonably early, I walked from Burton Bradstock to the far end of Cogden and back, with the recorder going. Lots of birds on the move. I tend to be a lazy counter, but 300+ Jackdaws heading west made it into print. My first Redpoll of the autumn too. No Siskins though. Well, not until I sat down this evening and had a flick through my recording. I only checked a fraction of it, but at least three times I spied the tell-tale shapes, and sure enough...Siskins. Whatever birding skills I once had are definitely on the way out...

However, I can spot big white things. So when a Great White Egret tried to sneak across Cogden airspace I was on it in a flash. Mind you, the camera was a bit slower than me...

My first GWE since this time last year, when two flew W past Cogden, just offshore


They might be an everyday sight in many places - in silly numbers too - but Great White Egret is still a pretty scarce bird locally.

Finally, for a change it wasn't a Wheatear which perched up in obliging fashion this morning...

Meadow Pipit

Meadow Pipits never let me get that close. Presumably that's a look of astonished pity...

'Seriously? You can't hear those Siskins?!'

Saturday, 9 October 2021

Not Quite the Horn of Plenty

Since the last post there are five new entries in my smartphone's notes app, one each for Tuesday to Saturday. One of them is quite unusual...

5/10 West Bexington 15:40 -

And that's it. It was so uneventful that I didn't even bother with a finish time. I'm not sure when I last noted absolutely nothing at all, but to be fair it is a very rare event. Birding on the coast is not necessarily a daily cornucopia of feathery wonder. That said, there is usually (apart from 5/10) something to photograph...

6/10 A Cogden Wheatear

6/10 Flavour of the moment - Cogden Meadow Pipit

6/10 Autumn Thrift, a sad shadow of its vibrant springtime glory

7/10 East Bex Wheatear on WWII beach furniture

7/10 West Bex Guillemot

7/10 This year's Med Gulls looking too cool for their socks

7/10 West Bex Phalacrocorax phalanx

8/10 Cogden Scoter

There's a story attached to a couple of the above...

Guillemot. Crunching along the West Bex shingle, I spied in the distance an auk corpse stretched out pathetically on the beach. It was lying on one side, its head flat against the pebbles. I strode towards it to check for rings, digging out the camera for an in memorium photo. As I drew near, the bird's head suddenly reared up. Next, it scampered rapidly towards the sea, rushed in and instantly disappeared below the surface. Fairly soon it popped up, and then paddled about in a worryingly lop-sided fashion. Mind you, this is the first time I have been fortunate enough to witness a resurrection.

Common Scoter. Distant, black, sleeping blob. Obviously a Common Scoter. There's been a few about I hear. I walked away and ignored it. Several minutes later I could see it had woken up, following the close passage of a motor-boat. It was just beyond binocular range, but surely a Common? Once upon a time I found a young drake Surf Scoter off Beer. It too was alone. So I walked down the beach again for a closer look. Still too distant. Resting the camera on the beach for stability, I took some shots at maximum zoom and checked the results with restrained optimism. Sigh... No glory today.

9/10 Oh look! Another Cogden Wheatear

9/10 Cogden Whinchat...

...times two

It's funny. Here we are in October, the season of seriously rare, and my last five outings have produced nothing more than a modest tally of common migrants. A quick perusal of BirdGuides or Twitter tells me that I am missing out, and would do a lot better here, or here, or perhaps there. So why am I not dissatisfied with my paltry lot? How on earth can I see barely anything at all and say it's actually enjoyable?

In truth I cannot really answer those questions. But I'm not dissatisfied. And I really have enjoyed my recent outings, even 5/10 West Bexington 15:40 - ...

In the last 24 hours I've watched a Temminck's Stint become a Least Sandpiper (not for the first time!) and then finally a Long-toed Stint, a species which almost everyone 'needs'. This is a metamorphosis which at one time would have got me all the way to Yorkshire. Why not now? I really do not know, but am very happy to remain unmoved. I often wonder at this apparent dichotomy between the old me and the current version, but know which I prefer.

Monday, 4 October 2021

The Scilly vs Shetland Question

With rain forecast to arrive around lunchtime I squeezed in a quick late-morning walk at Cogden. Atlantic-style weather is dominating at the moment, so my expectations were very low. But you never know...

The first field I tried yielded a trio of Whinchats, which was a delightful surprise...

Two of today's three Whinchats

The other, more cooperative one

Factor in 4 Chiffchaffs, 25+ Meadow Pipits, at least 11 Skylarks, 55+ Swallows and a Sand Martin, and it was an enjoyable walk. I scanned the sea many times, hoping the brisk SW might offer some thrills, but saw not so much as a single Gannet.

Yesterday's blog post was fun to write. Scilly always comes to mind at this time of year, and the current output of Twitter keeps it there. Shetland also. The birders on both archipeligos regularly post photos of the star birds, and very gripping they are too. At the moment it appears that Shetland has the lion's share of rarities, and already (on October 4th!) we have seen one or two tweets in the 'Yep, Scilly's definitely had its day' vein. Always makes me chuckle. I've written on this subject before, but as it seems topical...

Unless the only criterion that interests you is the total number of rare and scarce birds, the Scilly vs Shetland argument is a classic exercise in comparing apples with oranges.

When you arrive on Scilly, you are faced with roughly 16km² of well-vegetated habitat. Assuming you are physically capable, you can walk from one location to the next. If you fancy twitching a bird found at the other end of your island, you can walk there in less than an hour. If it's on another island, you walk to the quay, catch a boat, land on said island and walk some more. Arriving on Shetland though, your playground is somewhat larger. With some 1,466km² to go at, accessing it all is a very different game. If you are based near Sumburgh in the south, and fancy twitching a bird at Skaw on Unst, you've got an 80-something mile journey ahead, including a ferry crossing.

When it comes to Scilly and Shetland, the question 'which is better?' is a bit meaningless unless you take into account a lot more variables than the rarity count. For most birders a visit to either is a holiday, so perhaps a better question would be 'which will I most enjoy?' And clearly there is only one way to find that out for sure.

But yes, obviously Scilly is better.

Sunday, 3 October 2021

Sixteen

On Saturday, 13th October 1984, a morning helicopter flight arrived on St Mary's and eager birders disembarked. I find it hard to believe that it is almost 37 years since I first set foot on the Scilly Isles.

I was so excited! Was Scilly going to live up to the hype? Our party of four was completed by fellow West London-based birder Brendan Ryan, along with Geoff Burton and Martin Warburton from Kent. We were based in Silver Street, a few yards from Porthcressa and a short stagger from the evening log call. Having dumped our luggage, the next step was easy...

There was a Common Yellowthroat on Bryher.

With hindsight I am not in the slightest bit surprised at what I then did, but at the time I still had a few things to learn about myself. The other three made straight for the quay, and the next boat to Bryher. Not me. There was this sketchy rumour of a possible American Robin at Borough Farm on St Mary's, and I decided to head that way to see if anything came of it. Basically in the exact opposite direction to everyone else. On my own. I remember seeing a Red-rumped Swallow, but very little else.

The Yellowthroat showed well.

At this point I should mention that my notebook for that trip no longer exists, and I cannot recall in detail (or even roughly!) the day-to-day events. However, I do know for sure that my first trip to the Scilly Isles bagged me 16 ticks. Sixteen! And Red-rumped Swallow was the first. The next morning I was one of a small group of birders on Bryher who enjoyed terrific views of the Common Yellowthroat in its favourite little apple tree. Tick number two.

I have tried hard to remember all the species that were new to me on that trip, but can only think of 14, maybe 15. At least three of them were seen later that Sunday: Woodchat Shrike, Little Bunting and Blackpoll Warbler, all on St Agnes.

I shall just list some of the others: Ortolan and Rustic Bunting, Melodious Warbler, Short-toed Lark, Dusky Warbler, Olivaceous Warbler. In some cases not just one bird either. Rustic Bunting twice at least, Little Bunting ditto, and Ortolan on two or three occasions, including two birds together once.

One rare bird that wasn't a tick was Rock Thrush. A frantic but unsuccessful effort one evening, followed by a wonderful performance the following morning on the spectacular rocky outcrops of Penninis Head. Unforgettable.

What struck me was the seeming abundance of quality. A long wait for an elusive Dusky Warbler on Tresco was made more than bearable by the presence of Melodious Warbler, Ortolan Bunting and Red-breasted Flycatcher in the same spot.

A few photos...

The Scilly virgin, Old Grimsby, Tresco.

And the old hands. Brendan (on the left) and Geoff.

I quickly learned lessons which would stand me in good stead on future visits. Though initially bemused by birders donning full waterproofs prior to an inter-island boat trip on a dry, sunny day, well...

A lovely day. But windy!

I don't know how many birders were on Scilly in mid-October 1984, but definitely lots...

Rustic Bunting by the Garrison football pitch. Brendan with my scope. Needless to say, we had already seen it.

Rustic Bunting on Tresco a couple of days later.

In those days I carried a camera at times. A cheap Zenit B SLR and equally budget Helios 500mm mirror lens...

Super-tame Dotterel on the Golf course

Tawny Pipit on Old Grimsby beach, Tresco. I've a funny feeling that Somerset (but then West London) birder Jeff Hazell might have found this bird.

Eastern Olivaceous (but then just Olivaceous) Warbler, Watermill

On our last day, we set out in the morning with little expectation. I'm not sure what time we were booked on the chopper, but late enough that we were able to respond in a full and satisfying way to the staggering news that an Eye-browed Thrush had been found at Salakee Farm. It was a gob-smackingly gorgeous male, and liked to perch on cow pats...

Eye-browed Thrush twitchers, along the path from Salakee Farm to Porthellick

I used to dabble in pen & ink in those days but almost never used pencil, and I'm not sure why I waited three years to do this, but hey-ho...

I think it would be difficult to envisage a more thrilling finale to my first Scilly trip. Eye-browed Thrush was an absolutely mythical bird back then. When we later boarded the chopper I think most of us were already airborne.

Looking back, that one-week holiday could hardly have painted the gorgeous Scilly Isles in a more favourable light. The islands won my heart then, and have had it ever since.

Friday, 1 October 2021

A Strained Relationship

In past NQS posts I may well have expressed a love of seawatching. Well, all I can say right now is that seawatching and I need a bit of relationship counselling, because I am rapidly falling out of love.

On Monday morning I tried an early one at Cogden. I sat down, made a note of the start time, and ended up going home for breakfast without troubling my notepad any further. This morning I forgot to enter the start time and wound up writing nothing at all. In fact, within 15 minutes I realised it was going to be slow and found myself suddenly eager to leave. I think I stuck it for about 30 minutes. Tuesday was a little better. Cogden again, 11:00 - 13:00 and a strong SSW. I noted 19 Balearic Shearwaters, 18 Kitts, 2 Common Scoters, 2 Arctic Skuas and 9 auk sp. What those figures fail to convey is how deeply unsatisfying it all was, because almost everything was at mega-range, and there were several interesting but totally unidentifiable dots. The only redeeming aspect was a constant to-ing and fro-ing of Gannets, so there was almost always something to look at and check. Even so, two hours were plenty.

Yesterday was quite stormy, and under normal circumstances I would have looked forward to a bit of seawatching. Unfortunately I was in Exeter most of the day, but one of the local birders did spend four hours at Cogden, reporting 2 Arctic Skuas, 1 Balearic Shearwater, 1 Little Gull and a juvenile Sabine's. I've seen just three local Sabine's Gulls, and none of those while seawatching exactly. I'd love to see another, but the thought of sitting through four hours of Gannets in order to do so... I just can't get excited about it.

Spring seawatching is one thing, and the prospect of spoony Poms will always be a draw. At least I hope so. But autumn? That's a different thing. I can't remember the last time I had a really enjoyable autumn seawatch locally. And I've noticed that mobile birding is more and more appealing to me these days. I'd much rather walk for two hours and see not much, than achieve a similar result on my backside.

Anyway, what else has been happening since last weekend's Caspian Gull? Not much really. Apart from the seawatch tally mentioned above, five outings have netted 2 Chiffs, 2 Wheatears, a Whinchat, a Green Sandpiper and about 8 Snipe. Pretty feeble.

A Sparrowhawk on the beach last Sunday was a nice novelty though

East Bex Wheatear this afternoon, in ex-maize field

Looking at the weather forecast right now is pretty depressing. An unrelenting procession of Atlantic-based gank. Mind you, if I was a keen seawatcher...

 

Update - 2nd October

The original version of this post included the following:

The blasting wind has largely emptied the coast of gulls and, unlike last Saturday, this afternoon there were none at all in the East Bex fields, and no Med Gulls anywhere. I came across one small group of large gulls on West Bex beach - less than ten birds - and one looked interesting. Looking into the sun, the light was abysmal, but...

On the left: 1st-winter Yellow-legged Gull. On the right: 2nd-winter Herring Gull

Through bins it was too distant and poorly lit, and I couldn't nail it, but the camera persuaded me that a bit of effort was called for. I walked further west, then down on to the beach and back towards the gulls. The light was side-on, but much better. Just as I was lining up for the first photos, someone on the coast path spooked the lot...

1st-winter YLG in 60% of its glory

Okay. First of all, that is definitely not a Yellow-legged Gull. For a start, the scapulars should be much more strongly marked, with obvious dark anchors etc, and the greater coverts should be more obviously chequered. So what is it? The options are Herring Gull, Caspian Gull, Lesser Black-backed or hybrid. Without going into detail it is pretty easy to rule out Herring Gull and Caspian Gull, which leaves us with the last two. To suggest it's a hybrid would be a weasely cop-out, so I shall just put my hand up and admit that, as Tim suggests in the comments below, this is a pretty bog-standard Lesser Black-backed Gull.

In reality gulls fool me all the time, but not many get as far as the blog before I realise what's happened. I briefly contemplated removing all reference to this cock-up, but perhaps it is better to leave it here as a salutary lesson. One of the reasons I love gulls is because they are such a challenge. They stretch my ID skills and force me to learn new things. But gulls are hard. Mistakes are inevitable, and I would imagine that all of us who enjoy getting involved with gulls make plenty of them. So here's a nice (and hopefully rare) public example of one of mine!

Gulls keep you grounded. Always look at them. [wry grin emoji]


Wednesday, 29 September 2021

A Typical Caspian Gull?

As any gull enthusiast based in the South-west will tell you, Caspian Gull is still a rare bird down here, or at best very scarce. For example, the Dorset totals for the last few years look like this: 2015 (2), 2016 (1), 2017 (5), 2018 (8) and 2019 (5). The count of 8 in 2018 is the highest one-year total so far. In a brief Twitter exchange with Mark Golley I learned that 2018 was the best-ever year in Norfolk too, with a staggering total of almost 140! Even so, and despite the big numbers, until a couple of years ago Caspian Gull was still a description species in Norfolk. As far as Dorset is concerned (plus Devon, Cornwall and Somerset of course), Casp is likely to remain a description species for a long time yet.

However, Caspian Gull is spreading inexorably westwards in Europe, and occurences on this side of the North Sea are bound to increase. Great. But unfortunately its tendency to interbreed on occasion with Herring Gull means that we will doubtless see a corresponding increase in hybrids and backcrosses, and the identification challenges they pose. What does this mean in practice? Basically, encountering a candidate Caspian Gull in the field presents us with just two choices:

1. Look away immediately. If that is our favoured approach, we need read no further!

2. Get stuck in. Try to nail it one way or the other.

Caspian Gull ID is a topic with the capacity to bore like few others, and this post should already be ringing all kinds of alarm bells. If gulls are not your thing, er...clang, clang, clang!

I have written this post for a very specific reason. At West Bexington, on Saturday 25th September, I found (very badly) a Caspian Gull. I would be the first to say that it was hardly a textbook bird, a 'classic' example of the taxon, but in this post my intention is to prove that it was a 'typical' example. My intention is to demonstrate that a Casp candidate can be analysed in sufficient detail to establish its identity to a degree which will satisfy not only you the observer, but also any records committee tasked with assessing your bird for the purposes of posterity.

A Caspian Gull is identified by a combination of features, which all examples of the taxon will show to some degree or other. But that phrase 'to some degree or other' implies a level of variability, and therein lies the challenge. Hybrids and backcrosses (and Herring Gulls...and Yellow-legged Gulls!) also will show these features to some degree or other. In January 2020 I wrote a post entitled How to Measure Your Caspian Gulls. It referenced a 2011 Caspian Gull identification paper written by Chris Gibbins et al, which aimed to objectively quantify some critical features, in order that you could numerically 'score' an individual bird. The reason I wrote that post was to make a case for the identification of a striking (but not classic!) Casp I had discovered on the Axe Estuary. A Devon or Dorset Caspian Gull is a major prize, and no matter how much they might wriggle I am not going to let one go without a fight! So...

In the Gibbins et al ID paper, 95% of their sample of 63 1st-winter Caspian Gulls scored between 12 and 24, with a mean of 18. So I reckon it is fair to say that a typical Casp will score around 18. The authors concluded that the upper limit for 'safe' identification as Caspian Gull should be 21; anything higher might not be pure, even though genuine Casps did score up to 25. What I intend to do now is analyse Saturday's bird, feature by feature, scoring each trait as we go. So this could easily wind up the most tedious NQS post ever... 

 

1. Extent of scapular moult

0     no first-generation feathers remaining
1     a small number (< 1/3) of first-generation feathers remaining
2     a significant number (>1/3) of first-generation feathers remaining

Score = 1

So this bird would score 1 for 'extent of scapular moult'.

At this point I should mention that the Gibbins et al trait scoring for 1st-winters was aimed at birds in the period October to March, so at least one week older than this individual. I reckon it is highly likely that those few first-gen lower scaps will be moulted out very soon, so a score of 1 is a bit harsh. A nice, round zero would be the generous option, but we'll stick with 1 for the moment.

 

2. Greater-covert pattern

0     simple pattern with brown centres and sharp white edges, with no white vermiculation or notching
1     white edges with delicate notches or vermiculation; or dark brown centre with white tip to 1/3 of length (i.e. white restricted to tip or distal third)
2     clear white notches/barringcreating a delicate 'piano key' pattern along the whole edge/feather; but much of feather dark
3     lots of white (more than 1/2 of coverts looking white) distributed along the whole feather, or a bold notching ('piano key' pattern)

Score = 2

A score of 2 for greater-covert pattern is probably fair. If the inner coverts were still first-generation they would definitely be quite chequered, so despite the outer coverts being largely plain I couldn't give a score of 1. Even 1.5 would be a bit too generous I reckon. 

 

3. Ventral bulge

0     present
1     absent

Score = 1

 

4. Primary projection

As measured on a photo. This was about the best photo I had for assessing primary projection.  More or less a side-on view, and just about scrapes a zero score.

Score = 0

 

5. Moult: greater coverts

0     all or almost all new (>75%)
1     51-75% new
2     34-50% new
3     10-33% new
4     one or two feathers moulted
5     no moult

Score = 3


6. Moult: median coverts

Same scoring criteria as greater coverts above.

Score =3


7. Moult: tertials

0     3 or more new
1     2 new
2     1 new
3     all old

Score = 3


8. Darkness of head and body

0     totally white
1     reduced grey wash or streaking (confined to flanks and/or single streaks around nape)
2     light streaking/wash to head (incl. some dark around eye); isolated streaks/blotches on body. Overall, body looks more white than brown
3     well streaked: dark mask around eye and/or streaking covering the whole head/face; body with extensive but moderately dense streaks/mottles
4     strong and dense streaking/mottling on body and head making it appear almost wholly dark

This is another trait where my bird suffers due to youth. A few weeks older and it is likely to look a lot whiter. Even so it's not bad, and I am happy to give it a score of 2.


9. First-generation tertial pattern

0     Diffuse white tip (like Common Gull Larus canus)
1     fine pale fringe around distal portion (like classic michahellis), possibly also with some vermiculations
2     edges moderately notched
3     edges strongly notched and/or some dark barring or pale patches across the feather on some or all tertials

[See photo in 7]

The white part of the feather is restricted to the tip and does not extend very far down the edges. Also there is no notching. So although it doesn't quite match the description in score = 0, I still feel comfortable giving it nil points.


10. Second-generation scapular pattern

0     uniformly silvery-grey, darker patterning absent or very faint
1     silvery-grey background, pattern stronger than on 0, but lacks strong barring or central dark diamonds (only dark shafts and subtle anchors), with only a minority of such feathers (one or two) admixed
2     strong, contrasting shaft-streaks, anchors and/or dark central diamonds, but these more patterned feathers are less than half of all; ground colour creamy or silvery grey, possibly with some grey feathers mixed in
3     strong pattern described in 2 on most (more than half) of feathers, but possibly also one or two plain grey feathers or feathers with grey ground tone.
4     all feathers contrastingly patterned (with dark cross bars or diamonds), lacking plain grey feathers; feather centres buffy brown

Score = 3


Final score

Totalling up the scores for each trait gives the following:

1+2+1+0+3+3+3+2+0+3 = 18

As mentioned above, the date of 25th September means this bird hasn't really completed its post-juvenile moult. Which means it would likely score zero for 'extent of scapular moult' rather than 1, were we to revisit in December, say. Even so, a score of 18 puts it comfortably below the 'safe' identification threshold of 21. In fact, as 18 was the mean score of all genuine Caspian Gulls in the ID paper's sample, it would not be stretching things to call this bird an average, or typical Caspian Gull.


Additional evidence

Before we leave this bird, take a look at this pic...

Caspian Gull at rear, Herring Gull foreground - both in 1st-winter plumage

Notwithstanding the bird's slightly deformed bill (looks like a swollen lower jaw in fact) this gull has a very Caspish structure. High-chested (as if holding its breath), with drooping, attenuated rear end; quite long legs. All quite normal - and good pointers - for Caspian Gull.

Finally, that head and bill...

I took one of the photos, printed it out and literally performed surgery - with scalpel and sellotape - to produce this...

As the inset shows, not a particularly long bill, but slim, and with minimal gonydeal angle.

The 'bill shape trait score' was one of the characteristics which Gibbins et al used to help identify adult birds (not 1st-winters) and again it is a case of the lower the score, the better. I think I could have been a bit more generous with the scalpel, reduced the gap between the mandibles a little further and given the bird an even slimmer bill. This would have given a ratio greater than 2.47. In the ID paper, 87% of genuine adult Caspian Gulls (sample size = 100) scored 1, and the remaining 13% scored 2. Of the 12 confirmed hybrids examined, 43% scored 1, 25% scored 2 and another 25% scored 3.

Personally, I see nothing about this bird's head and bill to make me doubt its identity as a Caspian Gull, and the bill measurements support this view. 

Late Edit...

How could I forget the underwing?!


The superbly white underwing is a massively pro-Casp feature. Not all 1st-winters display such a clean underwing as this. The tail pattern is also spot on. Neither characteristic was used in the Gibbins et al trait scoring system, so all I shall say is that in the case of this individual, both unequivocally support the identification as Caspian Gull. As does the 'Venetian-blind' effect on the inner primaries, with sharp contrast between the dark outer webs and pale inner webs.


Conclusion

The conclusion actually is very simple. An objective analysis of this bird's characters, by means of the trait-scoring system devised by Gibbins et al, gives an unambiguous result: it is a typical Caspian Gull.

Question: do you think I applied the trait scores in a fair manner? After all, I did have a vested interest in a pro-Casp result. I would argue that even the most stringent application of this system would still leave you with a final score of 21 or less, and the nagging feeling that you'd been unduly harsh.

Lastly, a small soap-box...

All this talk of 'German muck' is doing the lovely Caspian Gull a massive disservice I think. The expression is unhelpfully pejorative, insinuating that any Casp which fails to display textbook or 'classic' (rather than 'typical') features, is genetically tainted. And if it is known to originate from a mixed colony...well...kiss of death! This is grossly unfair. In the preparation of the Gibbins et al paper, pure Caspian Gulls from the core range, with known provenance, scored as high as 25 on the trait score test. In other words, birds which are much muckier-looking than the one above can still be pure Caspian Gulls. And all of them deserve a warm hug.