Tuesday, March 30, 2021

Eyestrain at Farmoor

For my Oxfordshire birding I have somehow ended up adopting three patches - Port Meadow (the original and the best), Appleford (because of the gulls and the tip) and Farmoor Reservoir. Why I visit the latter so regularly is a mystery to me as I despise birding there - it is a featureless double concrete basin and on a bad day there is very little to even look at. I guess it's close to where I live and very convenient to get to from my office, so I end up popping in a few times a week. What draws me there is the potential for rarity finding, particularly at the roost, where the numbers of gulls eclipse anything seen at Port Meadow - probably at least ten thousand in the depths of winter.

The downside to this is the size of the reservoirs and the fact that the gulls prefer to roost right in the middle of F2, the larger basin, meaning that they are typically several hundred metres distant. To give an idea of just how far away many of the birds are, the video below starts at the maximum magnification of my scope (60x) before using the digital zoom on my phone camera to produce an acceptable record shot of a first winter Caspian gull. 

The distance means that even at 60x the birds are still tiny through the scope, so features like the exact pattern of the scapulars and coverts are very difficult to discern. Combined with the fading light it's an absolute recipe for eyestrain when trying to examine a candidate bird. Therefore at Farmoor, identification of Caspian gulls tends to be based on bulk plumage features (like white head, brown greater covert bar and plain tertials). This means that some of the more borderline individuals remain unidentified, or equally that some minor Herring gull features that might indicate hybrid origin are missed. Nevertheless, it is usually possible to identify most birds in the roost and despite the distant views the sheer number of birds makes for very entertaining roost watching.

Typical views of the gulls on F2.

Since September last year, I've had Caspian gulls regularly in the Farmoor roost - most of these birds are individuals that I've had better views of at other sites in the county, which makes identifying them much easier. I've posted some of these photos before, so here are a selection of birds that I've seen recently, together with some better images of these individuals from other sites!

1w in roost on F2.

Better views at Appleford earlier in the year, although still pretty distant. This is such an amazing bird, the best of the winter by far... that extreme scapular pattern, with just a single dark line following the rachis of each feather, is my absolute favourite plumage type in cachinnans. Interestingly, this bird was dark, with a rather streaky head and dusky underwing.

Massive 1w male on pontoon on F1.

This image was taken by Mick Cunningham, who found this distinctive bird during the day at Standlake. The heavy bill, indicative of a male Caspian gull, is evident here - this is also an extremely large bird. It has been seen at various sites in the county since October.

2w in roost on F2.

Showing P10 mirrors.

Same 2w in the field at Appleford.

This rather indistinctive 1w has been seen regularly at the Farmoor roost and also at Port Meadow - this superb image was taken by Joe Wynn as he chanced on it resting close on a pontoon on F1. Below is a video of this bird in flight over F2, on an evening where it was so windy that the only option was "seawatching" and identifying the birds as they flew into and around the reservoirs! All the relevant features for identifying cachinnans in flight are visible - note the clean uppertail with neat black tail band, white underwing, contrasty upper wing and the obvious neck shawl behind the white head.

A couple of Caspian x Herring gull hybrids were also noted.

This bird was regular in the roost in February and combined the clean coverts and tertials of Caspian gull with a Herring-like head and bill. Perhaps unsurprisingly it bore a yellow ring.

The putative 2w Viking gull deserted the Port Meadow roost at the beginning of March and moved to Farmoor, where it took a strong liking to one of the blue buoys and roosted on top of it each night. Its bulk meant that it was quite dominant over the other gulls and it had no problem removing an incumbent gull from the buoy and then defending its post for the rest of the evening. In the light at the Farmoor roost the uniform beige colouration of the underparts (actually darker than the pale grey mantle feathers) was evident. All equivocal I know as these fine vermiculated plumage features can be shown by pale 2w Herrings. But to have all of them in one bird combined with a Glauc-y structure makes me suspicious and having studied it at length I think there's a pretty strong case for a hybrid here.

Yellow-legged gulls are regular at Farmoor with double-figure counts on some nights, particularly in late summer/early autumn. Some images of 1w birds below.

Small gulls, mainly black-headed gulls make up the bulk of the Farmoor roost and searching through thousands of identical individuals each night can be rather tiresome. Nonetheless there are rewards to be had - these two 1w kittiwakes appeared on F1 after a south westerly blow on 28th October.

Little gulls are regular in spring but much rarer in the winter roost so I was pleased to find these two 1w birds on 8th November.

The main passage of Mediterranean gulls occurs in March with smaller numbers in October and throughout this season I recorded a large number of individuals of all ages. In March, it was rare that I visited the roost without seeing a Mediterranean gull - the status of this species really has changed in the county, with a couple of local breeding pairs.

Numbers peaked at four on 6th March, which included two birds that were obviously paired and engaging in courtship behaviour. This consisted of chasing each other around calling and swimming in tight circles looking intently at each other. Strange beasts. These inseparable birds visited continuously for a couple of weeks and throughout their stay the thinner billed (presumably female) bird acquired a full black hood. 

I've noticed that early passage seems to consist exclusively of adults, with 1w birds only appearing in late March once the adults have petered out.

As well as the gulls, there have been a couple of other surprises - this cattle egret which few north as I was doing the roost on 2nd October was the first record for the reservoirs:

Whilst a ringed common crane from the reintroduction project on 12th March was another a good flyover and a patch tick.

In general, though, good finds have been few and far between... Hard to believe there wasn't a single white winger recorded in dozens of visits to the roost! I hope to rectify this dearth of finds during spring passage. Bonaparte's season is almost upon us and with a 1w bird moving east from Cardiff to Gloucestershire I'm hopeful that it'll end up at Farmoor in the next few weeks!

Monday, February 22, 2021

Hybrids and more

Despite the cold weather conditions providing interesting bird movements across Britain, birding on Port Meadow has been relatively uneventful. It has been relatively static in terms of Caspian gulls in the roost. I suspect I have almost reached saturation point with this species in Oxfordshire, in terms of identifying individuals that are wintering in the county - over 30 at the last count. I haven't found a new bird for several weeks (although doubtless there are probably some at Appleford), and combined with the lack of movement typical of January/February it's been a case of seeing most of the same birds again and again. Our regular 2w bird, which Adam has dubbed "Eric" has been roosting most evenings, together with a few other birds of various ages. 

"Eric" together with the pale 2w argentatus

Despite this, the roost has remained interesting with an almost continuous run of wacky hybrids, identification puzzles and straight-out "weirdos" that make gull watching such an entertaining form of birding. It is these birds that form the basis of today's blog post.

Starting on familiar ground, it was good to see XJNE back to terrorising the roost this week. It was also joined on one evening by two other Caspian x Herring gull hybrids, including remarkably a bird rung at the same Braunsdebra colony on the exact same day! A strange coincidence, although the birds came in separately and did not interact at all. Great to see the range of phenotypes that this mixed colony is throwing out - XJNE is a really nice bird, albeit with heavily marked greater coverts.

In stark contrast XJNJ is a real piece of muck, an obvious hybrid with clear cachinnans influence in many traits, with the scapulars, greater coverts, tail and underwing in particular being intermediate - it also has quite a thin bill and rangy structure - but other than that looking rather like a Herring gull. 

This third bird is very Caspian-like, and at distance in the Farmoor roost, for example, I think I would probably just have identified it as a dark Caspian gull. It has advanced moult with many replaced coverts and nice clean scapulars, coverts and tertials - all good features for Caspian gull. The underwing is quite streaky, as is the head, but these features can also be found on Caspian gull from the core range. Where it is less convincing is its structure and facial expression, although this was not immediately obvious at range as the bill is quite thin. I always find it confusing assessing facial expression on birds like this as any kind of head streaking changes all the contours of the face making it very difficult to tell if that classic cachinnans facial structure is still there. Having looked at photos of dark birds from Eastern Europe I struggle to reconcile the facial expressions of these birds with what I am used to from the birds that I have seen in Britain. In addition, the bird is quite small, and I do find that these (presumably female) birds can have very short bills and punched-in faces - see the last image in the set below for comparison and also this bird on Josh Jones' blog. However, I feel that this latest bird definitely has a very Herring-y look to the face, which is particularly evident in the third photo.

For comparison a presumed female bird with a tiny bill from February 2019

A new 2w bird has also arrived in the roost and for me is a good candidate for a Caspian x Herring gull hybrid, having a really Caspian-like facial expression combined with extensive head streaking, especially around the eyes. The tertials and greater covert patterns are an intermediate type, which could theoretically be found on either Caspian or Herring gull.

This dark, heavily streaked bird is probably a Herring x Lesser Black backed gull hybrid - with the added feature of a massively over-hooked bill! Its mantle shade was similar to Yellow-legged gull. It also has a yellow colour ring, although it's been too far away to read the code.

After the recent run of Easterlies I have been looking for yellow-legged Herring gulls in the roost, i.e. those "omissus"-types that originate from the Eastern Baltic. With several reported on the East Coast I thought it would only be a matter of time before one made it to the Meadow - small rewards, perhaps, but a goal like this keeps one going. I picked out this bird on 19th February and immediately thought it looked like a good candidate - the lack of any black on P5 would appear to rule out Yellow-legged gull, and the mantle also looked slightly too pale for that species. It had a strange, asymmetric primary pattern, with a complete P10 tip on the right wing (unusual in Yellow-legged gull) and a thin subterminal band on the left. However... this bird lacks the long P10 tongues typical of "omissus"-types and its head also just looks exactly like a Yellow-legged gull - really mean expression and heavy, blunt-tipped bill with massive red gonys. I guess this is also possible on large, male Herring gulls, but this feature, combined with the lack of primary tongues (although admittedly still perfectly fine for argentatus) and also the mantle shade (lacking the bluish hue that I am used to seeing with argentatus) make this a far from straightforward case in my opinion. I wonder if it is a hybrid, which would explain its mantle colour and Yellow-legged gull jizz. Or perhaps it is just a large, male yellow-legged Herring gull and I'm being far too fussy about something that isn't even a discrete population any more - "omissus" was invaded by pink-legged argentatus decades ago, thus the classic yellow-legged phenotype is heavily diluted. Either way a fascinating bird. According to Chris Gibbins, Eastern michahellis can also have much reduced, sometimes completely absent P5 marks, combined with much longer primary tongues...

As an aside, this bird, which I saw at Appleford in mid-December, seemed to me to be a far more straightforward yellow-legged Herring gull, despite the white head. Ticks all the boxes - argentatus jizz and primary pattern, combined with yellow legs. Unless of course it's another Caspian x Herring gull hybrid!

All the above birds make me think more and more about what really constitutes a "species" in large, white-headed gulls. As a biology student, I find it difficult to regard a group of populations that can freely interbreed to produce fertile, hybrid offspring as "species" in any proper sense of the word. However, I don't think they should all just be lumped into one! Genetic differentiation between these populations is complex, and often at odds with the phenotypes that we recognise in the field. For instance - Iceland, Slaty-backed, and Glaucous-winged gulls can in most cases be easily identified in the field using morphology, but mtDNA sequencing reveals that there is very little genetic differentiation between these species, possibly due to their recent evolutionary origin or periods of hybridisation. In other cases, evidence from mtDNA implicates whole or partial reproductive isolation despite overlapping ranges and some recorded cases of hybridisation.

There is also a very interesting discussion about whether the clinal variation in large gulls is due to local adaptation, differential trait expression caused by phenotypic plasticity, or hybrid swarms in the contact zones between different "species" populations. Put simply, are the large, frosty argentatus with pale brown primaries (from the "far North") like this because of a local, slightly genetically distinct population, a gene-environment interaction, or the introgression of Glaucous gull genes? The latter is actually what has been concluded by at least one research paper (Crochet et al., 2003), i.e. that most intraspecific variation in gulls can be accounted for by hybridisation.

A third complicating factor is the expanding range of species such as Caspian gull, which is moving rapidly westwards and hybridisation with argentatus Herring gulls is now frequent. Many of these hybrids cannot be sufficiently separated from individuals that fall within the variation exhibited by Caspian gull from the core range - data from ringed individuals of known parentage has shown that some second generation hybrids are virtually indistinguishable from pure birds. However, there is a particular "look" about many of these East German and Polish birds, and I would argue that in itself this is a distinguishable phenotype - very often combining a Caspian gull jizz with rather Herring-like scapulars and heavily marked greater coverts - XJNE being a good example of this form. These birds also tend to have a streaky plumage and a slightly Herring-y facial expression. Ronald Klein, who works on these hybrid colonies in Eastern Germany has thrown the name "Larus polonicus" around to describe this distinctive phenotype. Perhaps in Europe we will soon have names for these hybrid swarms, in the same way that birders in the USA refer to Cook Inlet and Olympic gulls - both identifiable hybrid populations.

What does any of this actually mean for the British birder wanting to identify a Caspian gull for their list? Potentially, a larger number of confusing looking birds in the next few years - instead of dividing these down the middle into "makes the grade for Caspian" and "non-Caspian" perhaps we should be recognising these as a distinctive and increasing hybrid gull and only safely identifying the most classic, obvious "Pontic" Caspian gulls. This of course means that we will be chucking many non-classic "pure" Caspian gulls into the unidentifiable bin - but for birders who value the integrity of their species list then this is probably the best option. For me, since I think the whole species thing is far more fluid anyway I prefer to simply pick out "Caspian-type gulls" and not care about the exact genetic provenance of any particular bird. After all, a bird that may look completely classic may contain Herring gull genes somewhere down the line, which would be completely impossible to detect in the field unless the bird was ringed and its parentage known. That isn't really what birding is about for me - it's about being able to pick out identifiable, unusual phenotypes in the field. I just like the fact that they look different to Herring gulls and come from the East!

For this reason I found the extensive debate surrounding the 2011 Rainham Slaty-backed gull rather strange - although it was right to correctly establish the identity of the bird, from my point of view, it wouldn't have actually mattered if the bird had turned out to have had some Vega gull influence (although the mantle colour has now been documented as easily within variation). It's a brilliant Siberian gull that's travelled thousands of miles to be here, and an absolutely amazing find regardless of its exact ancestry! I fear that if a Cook Inlet gull were to turn up in the UK it would generate little interest simply as there is no tick box on the British List for "Glaucous-winged x American Herring gull" (and no chance of it later being promoted to full species status!) - despite being a mega rare American vagrant. I find the devaluing of hybrid birds, especially gulls to be quite a shame and it seems purely linked to a listing mindset. It doesn't change anything about the the find (or indeed the twitch!) - it would still be a spectacular, visually distinctive vagrant - yet just because no chance of an extra tick I think most would pass it over. I hope to be proved wrong if one does turn up!

Friday, January 29, 2021

Past couple of weeks

Since my last blog post the water levels have been up and down constantly on Port Meadow creating varied conditions for birding. On some days birds are fairly close by providing excellent views on small islands created by the receding floodwaters, whilst on other days the entire field is completely flooded resulting in a "Farmoor Reservoir" type of experience - i.e. straining trying to identify distant dots on the water. 

The floods are still continuing to pull in large numbers of roosting gulls and despite the mid-winter feel of little turnover there have been some interesting birds present. Caspian gulls have continued to frequent the roost including this smart new 1w with a few grey 2nd generation coverts.

This 2w Caspian gull roosted on a couple of evenings - an individual that I have seen previously at Appleford Gravel Pit. I picked out both this bird and the 1w above in flight as they circled over the Meadow - checking the gulls as they are flying in is something I've been doing more and more of recently and I feel it has certain advantages over trying to pick them out on the water especially if the gulls are densely packed.

Note the P10 mirrors and the white tongue at the base of P10, both good indicators for Caspian gull

The regular 2w Caspian gull that I've also seen at Farmoor has also provided excellent views although seems to have become tattier and uglier as the winter progresses.

This 2w individual is a fascinating bird with heavily chequered inner greater coverts and plain brown lesser coverts reminiscent of Yellow-legged gull. I included a photo of it in the last blog post and speculated that it was a possible Caspian x Herring gull hybrid but have since obtained much closer views and I think that option is unlikely. If anything it has some michahellis genes in it, but I think it is probably within variation for pure Caspian gull. Although it has no P10 mirrors, the structure is very Caspian-like, with a long, thin bill and handing rear belly - legs are not as short as they appear in this image as the feathers are fluffed up against the cold. Pro-Caspian features also include the relatively unmarked outer greater coverts, mantle colour and pure white underwing. Hybrids with Yellow-legged gull apparently tend to be more heavily streaked at this age.

Yellow-ringed XJNE, which I first noted at Appleford has also been present in the roost for the last few days. Despite being ringed in a mixed colony at Braunsdebra, Germany (and almost certainly having some Herring gull genes judging by the chequered greater coverts). I think it's a great-looking bird, especially in flight - really white underwing and unmarked uppertail. It is very aggressive towards the other gulls and on several occasions I have heard it call loudly as it flies around. I have rarely heard Caspian gulls call but got some good "training" in London over Christmas with birds coming to bread and XJNE certainly sounds like a Caspian gull - a braying "honk" quite different to Herring gull. Personally I am of the opinion that most of the large white-headed gulls are just one superspecies complex so the question of "where to draw the line", which many birders seem to be obsessed about with regard to Caspian gulls becomes less relevant to me. I'm just happy to enjoy a bird like this that's come all the way from Germany to winter here.

This 3w bird was also an obvious Caspian x Herring gull hybrid, with a very Herring-like primary pattern. Note the brightly coloured bill - usually a pallid greenish-yellow in Caspian gull at this age.

Continuing with the hybrid theme was this brute of a 2w argentatus Herring gull. Although not an obvious Viking gull I would bet money on it being from the far North and there being some Glaucous influence somewhere down the line - all the feather markings are so finely vermiculated, it has a Glauc bill, uniform latte-coloured underparts and very pale tertial centres combined with brown pale-tipped primaries. The tail pattern, however, was quite Herring-y. A striking bird.

There have also been a few Yellow-legged gulls in the roost - I rarely bother to photograph these but the 1w was quite a smart bird and the adult had a slightly peppered iris colour.


Showing tail pattern characteristic of Yellow-legged gull


Of interest also have been continental interemdius Lesser Black-backed gulls - there have been a few of these in the roost recently, which generally have a darker mantle tone and more attenuated structure than graellsii.

Under lockdown restrictions I have avoided general county birding and largely kept to Port Meadow, which I'm lucky to have on my doorstep. However, since my Appleford patch is within cycling distance I decided to visit last week to check how it was getting on. There are currently very few large gulls on the Gravel Pit itself and instead they are now loafing in a flooded field just Northeast of the railway crossing. One of the first birds I laid eyes on was this adult Caspian gull - always hard to tell with the adults (especially as so many have similar bill markings) but I feel that this is a bird I've seen before, with comparatively short yellowish legs...

This 1w was a new individual to me and a nice classic bird.

This 1w brute has been around all winter and every time I see it I notice more Herring-y traits... it's comparable in my opinion to XJNE although has slightly less covert chequering.

So in conclusion a solid couple weeks of gulling - no stand-out bird, unlike the excitement at the beginning of January, but still pretty rewarding. Nine Caspian gulls (four 1w, three 2w, 3w and adult) plus two hybrids is pretty good going for the Meadow by the end of January - clearly it's been an exceptional winter for this species in Oxfordshire. Adam managed to grip me off with a 1w Med gull in the roost tonight though which I failed to connect with despite being on site. Will have to hammer March passage for that year tick...

Finishing off this post with an image of a fabulous Port Meadow sunset.

Eyestrain at Farmoor

For my Oxfordshire birding I have somehow ended up adopting three patches - Port Meadow (the original and the best), Appleford (because of t...