glaucoides & kumlieni

(last update: October 12, 2011)

Iceland & Kumlien's Gull 3cy January

(Chris Gibbins)

Here are some thoughts on 2nd winter kumlieni versus glaucoides that may help with birds in Western Europe. To preface these observations, I should add that I'm not really too experienced with kumlieni (so can't speak from long term experience with many birds), but I do look closely at all the 2nd winter
Iceland Gulls that I see in Scotland. Fundamentally, my thoughts are not new, so it is the statistics (see below) that are most revealing.

I get nervous with 2nd winter white-winged 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 (like this bird), while others have subtle shading in primaries in tandem with slightly darker overall plumage (this bird, still both categorised pale glaucoides-like birds on this page).
This incremental darkening continues through birds which are darker on tail, secondaries and inner primaries, until you reach birds like this one, with dark shading and clear sharp
fringes in the primaries.

Birds like this last one are often discussed as kumlieni candidates, partly or wholly
because their primaries are much darker than birds from the 'pale glaucoides' group. But these darker birds are simply at the end of a continuum, and I see too many 'dark' 2nd winter birds in Scotland (relative to other age groups) to imagine they can all be kumlieni.

So, my working model in Scotland falls back on what we have known for a long time, namely that kumlieni in Newfoundland are not just dark, but have
(i) a J shaped pattern on the outer 4 to 5 primaries 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 primaries.
So the overall pattern is like a subdued Thayer's Gull of this age. Many also already have a 'ghost mirror' on P10.

Of course this is not new, but some statistics help emphasise the point. I've just done a count, and 32 from 33 2nd winter kumlieni from Newfoundland that I have in my collection show this pattern. And it is not just the dark ones - even very pale/otherwise white kumlieni show this (e.g. this bird). Bigger sample would be better, but this high % is persuasive.

On the darker (assumed) glaucoides I see here in NE Scotland, the intensity of shading is uniform across all primaries, so they lack the
Thayer's Gull impression on the outer five primaries; actually on many the pigmentation is darker on the inner primaries (possibly due to fading on exposed outer feathers).

So, until we know more about 'dark glaucoides' I work with a rather a
strict criterion in Scotland - shading in the primaries is not enough on its own, with
acceptable kumlieni having to have this contrasting 'Thayer's Gull' pattern. Thus, despite the shading, birds like this (the very dark one in Peterhead) would not be
acceptable, given what we can see of the outer priumary patterns in flight. Ditto with
darkish birds like this one and the very dark one here. This is not to
say they are not Kumlien's Gulls, but if they are, then they show a pattern shown
by less than 5% of the Newfoundland birds.

If I apply these criteria, then I've only seen one good 2nd winter kumlieni here in
NE Scotland. This number makes intuitive sense to me, given how many kumlieni of other age classes I see.

These points, made by Chris, are agreed upon by Bruce Mactavish, who sees lot of kumlieni in Newfoundland, where he lives. He did notice on some of the suspect Kumlien's from various parts of Europe in the last few
weeks of January 2012 (largest influx in W Europe of white-winged gulls ever), that the dark on the outer primaries of some birds did cross on to the inner web, which doesn't look right for kumlieni.
On one bird there was a uniform darker shading across all the primaries and even across the secondaries. This is not right for normal Kumlien's Gull which typically have whitish or very pale secondaries, definitely much paler than the outer primaries. Second winter Kumlien's Gull exhibit the darkest colouring of any age. The two-toned impression (by the dark outer-web and pale inner-web of outer two to five primaries) is more obvious at this age than in 1st winter birds.

3cy birds with pale outer primaries: classic glaucoides

overall dark birds, with inner primaries darker than outers, probably glaucoides

overall pale birds in Newfoundland, kumlieni

birds with dark outer primaries, classic kumlieni