Monday, 9 November 2015

A Colour-ringed CaspianISH Gull

What a fascinating bird.  I've felt a complete spectrum of emotions over this bird, the usual elation at finding a Caspian Gull, then suspicion, confusion, inquisitiveness, disappointment, intrigue, disappointment again, perplexment, wonder.... and honestly I could go on!

I've been checking the gulls as often as I've been able to over the last few days.  There's been something of a Caspian influx in the south east, and we've had a decent turn over of gulls on the Estuary in the recent rough and wet weather, including excellent numbers of Black-backed Gulls.  And this morning shortly before 10am I spied a distant first-winter 'Caspian' Gull from Coronation Corner...



The first view I had of it was the very back end of it as it was hidden by that Great Black-backed.  All I could see was a long wing, very dark tertials with noticeable white tips, and contrasting pale greater coverts. That was enough to stop me scanning and fix the scope on it. And I'm glad I did because it then walked in to full view and looked spot on. Lovely white head and upper breast, perfect head shape and bill, a fair bit of grey in the mantle, long legs, overall noticeable bigger than surrounding Herring Gulls. Excellent.  This was all good enough to text the news out.

It then took off flew a short distance and landed a little closer, but still pretty distant. And it was still a 'Caspian' Gull...




It did now look darker than all the other Caspian Gulls I've ever seen here, the streaking behind the birds head is ok, but all that down the flanks and belly and particularly around the eye worried me a little. But not too much, it's still early November. It showed some really aggressive behavior as well, often stretching its neck out to poke its beak at a nearby landing or low flying gull  It was only now I noticed it had a green ring on its leg too, and thankfully Dad who was positioned in the Tower Hide (much closer) was able to read it. XVFM.  It then looked even better when it stretched its wing...


Excuse the quality of this pic, I was just taking the phone away from the scope when it stretched so I quickly pressed the button. Lovely crisp white underwing and slightly paler inner primaries.  I then found out thanks to Rich Bonser that a four letter coded green ring is a Caspian Gull ringing scheme in East Germany, coordinated by a chap called Ronald Klein.  I really was elated by this, we had nailed a ringed Casp on the Axe. Epic.

It then took off and flew south, I didn't look at it much in flight as I was busy taking photos. But reviewing these it's still looking ok...




Again for a first-winter Caspian Gull it does look quite dark underneath, but wing pattern still ok with a lovely dark secondary bar and narrow white lines either side of it, and a restricted pale inner primary window, although it is missing the classic dark greater covert bar.  Seems to be a good Casp tail pattern too.

I thought this was it going, often large gulls do this and disappear out to sea never to be seen here again. But to my amazement it dropped back down on to the mud lower down the Estuary.  So I jumped in my car and followed.  Within about a minute I was there, and looking forward to the prospect of getting some top notch patch Caspian Gull photos as it would now be much closer. My bins went up to check which of the two settled large gulls it was, and... "what the ****!"

This is when the cycle of most of the emotions mentioned in the first paragraph of this post began.  To my eyes this no longer looked like the Caspian Gull that is was, not by a long way....




Eughhhhh. Overall shape, bill, legs, head shape, mantle and I think tertials (although not perfect) still ok. Not to mention the perfect Caspian Gull ring! But it just looked gross.  Except for the lowest two or three, the greater coverts are far from being plain, too many notches and bars surely? And now all that streaking around the head (especially the eye), neck, flanks and belly did indeed look too heavy.  PANTS.

I've sent the ring details in, along with some photos, and will post what comes back. And please I would love to read other peoples opinions on this bird. But in my view this is just not Casp enough and it's got to be a hybrid (presumably with a Herring Gull?).

It's only thinking about this some more though that I am starting to feel more positive about this bird, how many confirmed definite Caspian hybrids have been recorded in the UK? Certainly none in Devon anyway. This could turn out to be the most educational gull that I've ever seen.

As I said, all comments welcome please, and I will post the ringing details when I have them...

12 comments:

  1. HI Steve, Doesn't look great as you say based on the last couple of photos - even the flight shots don't seem to show the upperwing strong double dark wing bars exhibited by most Caspian Gulls and they usually look longer out the front end too. On the closer shots, it has more of a herring gull jizz, rather short legged, facially and even bill (which may be a little longer) but still has the prominent gonys closer to Herring or Y-lGull. It looks quite long winged but the horizontal stance is more like Herring and lacking the high chested necky look of Caspian. The upper wing covert pattern is not right for Caspian - not dense enough. You need to find out more about the ring too - was it only Caspian Gulls being ringed with these green rings?

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    1. Hi Mike, as ever a detailed and impressive response from you! Maybe you'll just have to take my word that at distance it did look very good for Casp, shape and all. It was big too, quite beefy. Makes me wonder though how many distant Casps are claimed across the UK and not actually nailed properly, especially where they are 'expected'. I will be looking closely at any green ringed Casp photos I come across!!

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  2. Hi Steve - odd bird - looks like a casp head stuck on a herring body - most worrying mantle/scaps and all wing coverts - surely a hybrid? Having said that I've seen a tonne of photos of birds that are far from classic casps. Think this one just has too many things going against it as per Mike's comments. Apparently hybridization is all too common. Will be very interesting to hear what Ronald Klein says.

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    1. Hi Matt, I knew you would comment, thanks very much indeed. Although I am gutted it didn't turn out to be a cracking first-winter Casp, its been very interesting and nice to see what I'm sure will turn out to be a definite HerringxCasp hybrid.

      All the best, Steve

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  3. Hi all, as I said to Steve earlier, from the ring code this bird comes from a mixed colony - Caspian and Caspian X Herring - in the far east of Germany, an area notorious for such hybrids. What the parents were we'll probably never know unless a blood sample was taken. As Mike said, structurally it doesn't look good for Caspian - horizontal, legs a bit too stout, no sagging 'belly' or high breast bulge, the bill's not too worrying - they're not always slim with no gonys. Moult appears very advanced for Caspian (and clearly wrong for argentatus), a couple of inner GC and most of MC look 2nd gen. There's actually a hint of michahellis about it given structure and moult stage. I know the underwing and the inner PP look pale but eastern Micks - which do turn up now in that part of Europe - apparently can look alarmingly different to our 'usual' W Med or Iberian birds.

    As you may know, Lee had a 1y bird on the Warren last winter, ringed in Lithuania and presumably from just such a mixed colony.

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    1. Tim thanks very much for the comment and phone call earlier... I had a feeling you would enjoy this bird, and to be honest I'm surprised it didn't drop down in front of you as you seem to attract odd gulls!!

      Interesting reading your mich comments. Must try and get out there myself and see what's going on.

      All the best, Steve

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  4. Hi Steve. Your bird made me dig out a description I did for that enormous Casp we had in Dec 2011. At the time, Part 2 of 'Caspian Gull ID' by Gibbins et al had just been published in BB. It suggested assessing certain features (the paper called them 'traits') on a bird in a numerical fashion, rating them 1 to 5 based on the trait descriptions in the paper. The traits to look at were: extent of scapular moult, greater covert pattern, ventral bulge, primary projection, moult in greater coverts, median coverts and tertials, darkness of head and body, first generation tertial pattern, and second generation scapular pattern - 10 traits in all. The Dec 2011 bird scored 20 by this method. According to the paper, true Casp should score 12-25, so that bird fitted in just fine. This gelled with what it looked like in the field - you couldn't really think it was anything other than a Casp!

    Additionally, a true Herring Gull should score 29-37 and - tellingly - a hybrid 22-32. That's quite an overlap zone! Steve, I reckon if you were to put your bird through that process it would not cut the mustard as a pure Casp. Even the Dec 2011 bird was only 2 points short of the overlap zone!

    I'm afraid I don't have the paper any longer - my BBs have bitten the dust. It isn't available online yet either, but I'm sure Mike or Matt etc will be able to help?

    Anyway, visually I'm right there with you - looks very interesting from a distance, but up close it's...er...a bit grim! I look forward to hearing what the ring reveals!

    ATB, Gav

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    1. Hi Gav. I reckon my bird will get a minus score!! Thanks for the comment and the phone call, and hopefully one of us will turn up a 'pure' one tomorrow!? If not, I'll let you know if XVFM drops in again.

      Best wishes, Steve

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  5. Wow, amazing looking bird. Well sorted out my friend.

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    1. Cheers Brett. How we love these large larids...

      Take care mate and see you soon, Steve

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  6. Great stuff Steve and well persevered. As always and as you know only too well, caution required with all gulls! Ironically as discussed the other night! Will be keeping an eye out on the Otter tomorrow.

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    1. Hi Chris, thanks for the comment. Yes I thought this bird was very timely following on from last week DBRC's meeting. Shows we do indeed need to be cautious about poorly seen or poorly documented Casp sightings. And also be cautious about colour-rings!

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