Adult Kumlien’s Gull Primary Pattern

Adult Kumlien’s Gull

Few gulls show as much variation as Kumlien’s Gulls. The identification of these fine gulls has been much disputed. Especially younger birds can be tricky to work with. But generally it is agreed that any adult “Iceland Gulls-type” showing some grey or black colouration on the outer the primaries can be safely identified as a Kumlien’s Gull.

The variation of these patterns on the primaries is enormous ranging from a whole black pattern closely resembling that of Thayer’s Gull to an almost totally white wing with only faint ghostly markings.

Without going into details about whether Kumlien’s Gull is a hybrid swarm, a subspecies or a full species the purpose of this blog is to show the variation of primary patterns that I have seen during the Iceland Gull invasion in january and february 2012 on the Faroe Islands.

It is almost impossible to say what a typical kumlieni-pattern looks like. It is simply too varied, but it is possible to show what I’ve seen so far and which patterns are most common.

Colour

The colour of the primary pattern is most often grey, but a few birds do show a solid black pattern. I haven’t seen any direct link between how extensive the pattern is and how black it is. Some birds have black outer webs on p10 and p9 and that is it, while others have a greyish pattern covering p6 to p10.

To make it more clear I’m going to post some pictures and comment below.

Kumlien's Gull with solid black markings on p6 to p10 - this is probably the one of the darkest Kumlien's Gulls possible before entering into the Thayer's Gull - area.

Very pale grey outer webs on p8-p10 and faint subterminal bands on p7-p9 creating the mirror-effect.

An intermediate pattern between the two above. Dark grey outer webs on p 7-p10, subterminal band on p6-p9 and even a hint on grey on the tip of p10.

Dark marking on outer webs of p7 - p10 and subterminal band on p6-p9. Here the p10 is slightly more grey the p9 which is darkest. P8,p7 and p6 gradually get paler and paler.

The four birds about show a “full” reflection of the pattern of Theyer’s Gull. There are both dark markings on the outer webs and there are a number of subterminal bands on the outer primaries. These birds are easy to spot in flocks of Iceland Gulls, because the mirror-effect created by the subterminal bands are obvious and eye-catching. But during the invasion only a minority of the adult Kumlien’s Gulls showed this striking pattern. Most birds did only reflect parts of the full Thayer’s Gull-pattern.

This bird only shows faint dark marking on the outer webs of p8-p10. There is no hint of any subterminal band.

A bird with a dark markings p9-p10. These birds are rather tricky to pick out in the field.

A bird with slightly darker dark outer webs on p8-p10, but still no hint of subterminal bands. These birds are not so difficult to locate among the Iceland Gulls as the dark markings are rather extensive.

Very faint grey outer webs on p9-p10 and maybe just a faint hint of a subterminal band on p9.

The patterns shown above are typical of most of the adult Kumlien’s Gulls seen on the Faroes. They do not show any or at least only very faint subterminal bands but the outer webs of the outer primaries have some shade of grey or black.

A few birds have shown obvious grey subterminal bands on p8-p9 without showing significantly darker outer webs on the outer primaries.

There are some very faint marking on the outer webs on this bird, but the subterminal bands on p8-p9 are the darkest markings on the primaries.

Again a bird with dark subterminal bands but no other dark markings on the primaries.

A shot of a wing showing subterminal bands on p7-p10 but with no other obvious dark markings on the outer primaries.

All in all we can say that there are three groups of primary patterns on Kumlien’s Gulls (or “Iceland Gull-types” with markings on the primaries).

1. Birds can show a full reflection of a Thayer’s Gull-pattern with both dark outer webs and subterminal bands on the outer primaries. The colour tone can range from solid black to faint grey.
2. Birds can show dark markings on the outer webs on the outer primaries without showing any subterminal markings.
3. Birds can show subterminal markings without showing dark outer webs on the outer primaries.

When dealing with adult birds it is quite straight forward to say that the markings are not age related. But how this applies to younger birds is more of a challenge.

SiO