Identification of second winter kumlieni
Posted: 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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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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