Larus glaucoides Kumlieni...?

[Helder]

Hello,

Yesterday i´ve found this glaucoides in Peniche, Western Portugal (my local patch).

I´ve identified it has a kumlieni...but would like read other opinions...can it be a darker glaucoides?










Many thanks,

Helder Cardoso

[marsmuusse]

Hi Helder,

1st cycle / 1st winter birds are difficult to separate, except of course the very straightforward glaucoides and kumlieni. For kumlieni we do not have a complete picture of the characteristics to identify these birds. Actually it is pretty simple: birds that are very pale are not uncommon in Newfoundland and their numbers should suggest at least some of these paler 1st cycle birds will turn into probably normal looking kumlieni (but limited ringed birds still). This is in line with the adult plumage: pretty strict criteria for glaucoides and a swarm of feature found in kumlieni.
Having said this, I recently added some birds to ORG, and three criteria were used to at least separate the most obvious birds is 1st cycle:

- outerwebs of the outer primaries are the darkest part in the primaries in kumlieni. Some glaucoides may show dark on the outer primaries, but these are pretty dark birds overall, with the inner primaries at least as dark as these (dark) outer primaries.
- solid tail band in kumlieni, less vermiculated.
- secondary bar by dark (outerwebs) of secondaries, the brown hue darker than the brown tone on the greater coverts, resulting in dark band on secondaries. This band can be less conspicious when the feathers are spread completely (or angle to observer is different) as the innerwebs of secondaries may be surprisingly paler.

Just some thoughts, love to here comments from people with more experience with this taxon.

Mars

[Helder]

Hi Mars,

Thanks for the reply!

Yes, are difficult indeed. I have little experience with this taxa..i´ve observed some 1cy L. g. glaucoides in Peniche, and one kumlieni 1cy a few years ago..but were all typical birds. This one just seem so show some features for glaucoides and some for kumlieni...

The secondary bar and tail band look quite weak for kumlieni, but primary colour does not look bad darkening a little towards wing tip.Very dark bill, with just a faint pale tinge and dark iris.

I think i will keep this record has a "putative" kumlieni. I´ve relocated the bird again today and spend more time watching the plumage under different light conditions..but still quite puzzeling...

[adriaens]

Mars, most 1st-cycle Kumlien's Gulls have pale secondaries (though I agree it depends on the angle of viewing to some extent).
This is actually a key feature to separate them from Thayer's Gull.

Helder, your bird looks like a typical Kumlien's Gull to me.

[marsmuusse]

Hi Peter (not sure if you're already in the plane),

I know there are kumlieni with pale secondaries, like there are also kumlieni with pale outer primaries, and glaucoides with darker outer primaries. Question will be: "will such birds ever be acceptable as vagrant birds?".
I think when birds show all three mentioned criteria, we find ourselves maybe in the safe zone?
I agree the bird Helder photographed is a very good kumlieni candidate, but we also have to agree on the criteria.
Hopefully 3 criteria will do the job (but still we have to define elements in the set), but if the job can be done on only two, that would be great.

Strongest point probably is pigment in outer primaries, but you should be careful. Personally, I think the bird below, with dark outer primaries, is probably still in glaucoides camp: