Identification of second winter kumlieni

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Ruud Altenburg
Posts: 248
Joined: Sun Sep 27, 2009 1:58 pm

Identification of second winter kumlieni

Post by Ruud Altenburg » Tue Jan 24, 2012 5:57 pm

Currently unprecedented numbers of Iceland Gulls reach the Dutch shores. Today's maximum count was five at a single locality! Among these birds are a couple of very dark specimens, which are discussed in this topic. I have asked Chris Gibbins' opinion on second winter kumlieni. Chris took the time to write an elaborate (yet informal) reply, which I would like to share with you (with permission).


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Hi Ruud

Here are some thoughts and observations on 2w kums v glaucoides that may help with your birds. To preface these observations, I should add that Im not really too experienced with kums (so cant speak from long term experience with many birds; I've only had a single trip to St John's to study them) but I try to look closely at all the 2w Icelands that I see. Fundamentally my approach to dealing with birds in Scotland is not new (i.e. literature on ID features has been around for quite some years now), so it is the stats (see below) that are perhaps most revealing. OK, my thoughts:

I get nervous with 2w birds because I see large variability in birds in this age class in Scotland (more than other age groups). Some have effectively unmarked primaries and clean bodies (bird 1), while others have subtle shading in prims in tandem with slightly darker overall plumage (bird 2). This incremental darkening continues through birds like 3 until you reach birds like 4, with dark shading and clear sharp fringes in the primaries.

Birds like 4 are often discussed as kums candidates, partly or wholly because their primaries are much darker than bird 1. But birds like 4 seem to me to simply be at the end of a continuum, and I see too many 'dark' 2w birds in Scotland (relative to other age groups) to imagine they can all be kums.

So, my working model falls back on what we have known for a long time - that kums in NF are not just dark, but have (i) a J shaped pattern on the outer 4/5 prims formed by the dark outer webs contrasting with the pale inner webs, with these typically curving around or forming a subtle blob at the tip; this is combined with (ii) relatively pale and unmarked inner prims. So the overall pattern is like a subdued thayers of this age. Many also already have a ghost mirror on P10. Peter Adriaens has lots of great pics showing this typical pattern at http://www.aerc.eu/KumliensGull/index.htm and I'm sure he could contribute much useful insight into to this discussion.

As I say, these features have been known for some time, but but some stats help emphasise the point:

I've just done a count, and 32 from 33 2w kums from NF that I have from my trip show this pattern. And it is not just the dark ones - even very pale/otherwise white kums show this (e.g. img 4011). A bigger sample would be better of course, but this high % is beginning to get persuasive.

On the darker (assumed) glaucoides I see here in NE Scotland, the intensity of shading is even across the primaries, so they lack the thayers impression; actually on many the pigmentation is darker on the inner prims (possibly due to fading on exposed outers). On individual feathers the pattern appears patchy, with no apparent consistent contrast between outer and inner webs.

So, until we know more about 'dark glaucoides' I work with a rather a strict criterion with the birds I see here in Aberdeenshire - shading in the prims is not enough on its own, with my 'acceptable/identifiable' kums having to have this contrasting 'thayers' pattern. Thus, despite the shading, birds like 4 (Peterhead) would not be acceptable, given what we can see of it in flight (4b). Ditto with darkish birds like 3 (flight shot in pic 3d) and 7b. This is not to say they are not kums, but if they are then they show a pattern shown by a relatively small proportion (perhaps around 5% if my admittedly small sample from NF is representative) of NF birds.

Hope this helps/is useful Ruud re your Dutch birds..

As I say, the ID features in themselves are well established, so I in truth all im doing here simply outlining how I treat the birds I see in Scotland. There is still much scope for a proper assessment of the ID of immature kums, but IMO this needs someone to visit Greenland to look at glaucoides within its breeding range. In truth trying to work things out in Scotland is not the best idea.

Chris
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JanJ
Posts: 422
Joined: Mon Oct 12, 2009 10:08 pm

Re: Identification of second winter kumlieni

Post by JanJ » Tue Jan 24, 2012 7:34 pm

Interesting subject , which has become very much discussed at the moment following the massive influx in western Europe.
Regarding the primary pattern in the mentioned age class - and younger birds as well - as mentioned by Chris - the contrast between darker outer and paler inner primaries in so called typicall kumlieni is a well known feature agains no contrast to the reversed (compared to kumlien) in glaucoides. In Chris pic here - 4011 seems to be the one with a so to speak classic pattern. So the question would be, can some glaucoides match this pattern?

Latest post fro Birding Faroes.

http://birdingfaroes.wordpress.com/2012 ... -cold-day/

JanJ

Chris Gibbins
Posts: 20
Joined: Tue Nov 02, 2010 5:15 pm

Re: Identification of second winter kumlieni

Post by Chris Gibbins » Wed Jan 25, 2012 8:08 am

Hi everyone,

Thanks to Ruud for posting up our discussion on the ORG Forum; as Jan says, it is a topical subject given what is happening. Obviously lots more people know lots more than me about kumlieni, so the point I would like to emphasise is that my discussion with Ruud was simply the approach I adopt with the birds I personally see, rather than me outlining definitive criteria for kumlieni per se. Clearly the problem we have here in NE Scotland is that of drawing a dividing line in what appears to be more or less continuous variability - the variability is apparent because we get good numbers of white-winged gulls each winter. The only place where there seems to be some discontinuity is the point where I draw it (as described in my mail to Ruud). If I 'move my line along' to include birds as kumlieni which lack the contrasts , then I suddenly have lots more 2w kumlieni here in NE Scotland. This would be inconsistent with the numbers of kumlieni of younger and older age groups that I see.

Ruud posted up some example birds from Scotland, so to add to these Ive posted 10 example 2w Kumlien's from St Johns NF onto my blog, showing variability in the birds there.

http://chrisgibbins-gullsbirds.blogspot.com

I have to be honest and say that Im struggling to find an entirely satisfactory way to deal with the birds I see here - I have a nagging doubt that my approach misses genuine kums - so more work is needed. I visited SW Greenland in August 2011 and chanced upon several places where good numbers of gulls were present. It was a work trip and I did not have time for gulling , so im rather keen to go back this summer and have a proper look....maybe such a visit will help us underatnd better the variability in glaucoides.

Chris

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