Tricky Juvenile Caspian Gull or hybrid?

Revisiting, Discussing, Learning

by Chris Gibbins and Steve Arlow

(2 honorable dudes who willing to learn, make mistakes and discuss openly – M.G.)

08-25-2013 Caspian Gull juvenile Pitsea Tip WEB 069

This bird has already been featured on Birding Frontiers >>>here<<<
Lot more photos and text at Birders Playground (scroll down).
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Original comment by  Steve A:

A very big and powerful looking bird that has all the traits of a Caspian Gull in terms of structure. The typical pale head contrasting with the rear neck shawl, small eye centrally placed in the face, the small head with sloping forehead, the long bill that here has a fairly pronounced gonys angle which isn’t to unusual in large males, but perhaps extreme? The tapering tip, rather than blunt tipped as in a michahellis should lean this towards Caspian. The streaking around the rear of the eye is a little unusual.
 
The hanging white rear bellow, the dark tertials with limited pale tips and fringes, the rather uniform wing coverts with fine pale edges, the dark bases to the greater coverts forming a dark bar across the wing, the kinked neck and high chest are supportive of Caspian however the under and upper-tail covert barring is a little heavy and the tones of the plumage might infer a hybrid bird.
So on the front of it looks like a likely juvenile Caspian Gull but it could have some genes in there that are not? Just back now and catching up on things.
,

Follow-up comments by Chris G.

 Yes, this is a very scary bird.  I’ve seen birds very like this in Lithuania – one in particular that I remember being both brown like this and robust and also with a good long call. This was maybe 4 or 5 years ago.  At the time I remember thinking ‘well, it must be a Casp, especially given the call and posture’.  But I have had a long time to reflect and have now of course seen Casps in both Azer and Ukraine… and I am now wondering whether such birds really are pure Casps.  Certainly there are more problem birds like this in the Baltic area in early autumn than there are in Ukraine and Azerbaijan, and with the proximity to Poland and more especially this newly discovered set of mixed colonies in Belarus, perhaps extra vigilance is called for?

Two or three points to make from Ukraine regarding Steve’s bird:

  1.  The vast majority of Casps were very easy, classic birds…. So this bird would certainly be odd in the core range. Not to say it isn’t one, but it is certainly far from typical.
  2. Most in Ukraine had many new scaps and wing coverts.  Most of the ones  which did not were clearly sick or injured and have presumably delayed normal moult due to stress. So both its plumage and moult stage are odd. And its angled gonys looks to much, even for a large male Casp (which tend to have thick but still parallel bills).
  3.  We did have several presumed hybrids in Ukraine…surprisingly quite a few birds (given location) which suggests that there are a lot out there in central and eastern Europe.  We had some interesting adult and 1cy birds (will do a post for frontiers)  and these have to make us think that in many underwatched places there must be hybridization going on. We then come back to the subjective point about where to draw the line between acceptable and non-acceptable birds…..no easy answer of course as its opinion….but to my knowledge no one has info on call or call posture of proven hybrids and so we may be best advised to work on the assumption that they may call and behave like either parent? So even the call may not be safe basis for ID of odd-looking birds like this.  We simply don’t know for sure, until we get a proven ringed one looking like this.

One a more general note we had lots of time to chat to Ukrainian gull folks about what is going on there.  There are now several places where michahellis type birds are in Casp colonies, so it is all rather a mess. Both species are expanding their ranges there (e.g. 20 years ago no Casps were breeding in Kiev ) so the whole situation seems rather fluid; they don’t know what is happening in large parts of the country as there are only 2 or 3 people looking at gulls. Black whole.

Anyway, the short answer about Steve’s fascinating bird is that I have my doubts, and have more since being in Ukraine.  I’m not sure though, and he could be correct calling it Casp; for sure some Casps can have dark underwings like this, but the darkness combined with structure and late moult are enough to raise significant alarms in my mind .

Chris

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About Martin Garner

I am a Free Spirit
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2 Responses to Tricky Juvenile Caspian Gull or hybrid?

  1. Jan Jörgensen (JanJ) says:

    Sound approach to this bird by Chris. However, regarding the bill shape – the impression differ by angle. In the straight profile shot it seems as good as it can get for cachinnans, perhaps even better compared to this bird (if you like):
    http://gull-research.org/cachinnans/1cy/1cyjuly03.html

    Nice pic By Steve as usual!

    JanJ

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