Sunday, 29 January 2017

Just a Common Gull?

28th January 2017 - Topsham


Well this one stuck out like the proverbial. A distinctly dark Common Gull and thoughts naturally turn to heinei*. But there's more to it than a dark mantle of course; first, here's the bird in question.

Common Gulls (and a BH Gull) - 28/1/2017 Topsham

Common Gulls (and a BH Gull) - 28/1/2017 Topsham

Common Gulls (and BH Gulls) - 28/1/2017 Topsham

Common Gull - 28/1/2017 Topsham

Common Gull - 28/1/2017 Topsham

Common Gull - 28/1/2017 Topsham

Common Gull - 28/1/2017 Topsham
I'm handicapped by not having a copy of the recent Dutch Birding paper by Peter Adriaens and Chris Gibbins (it's now on order) but I did get some information from Gull-Research.org  and this fascinating video presentation by Peter Adriaens.

Differences between heinei and canus (my interpretation of the bird in question in italics):

- heinei averages larger and longer winged, though with much overlap,
    impossible to tell though it didn't look significantly larger
- heinei has darker upperparts (some approaching pale graellsii?), though some overlap with canus
    certainly darker than nearby 'normal' canus
- winter heinei white-headed with only fine dark spots/streaks concentrated on hind neck,
    head and neck no different to 'normal' canus
- pale iris in many heinei,
    appeared to be dark
- bill and legs of heinei tend to be brighter yellow.
    legs did appear a little brighter yellow, bill apparently identical to nearby 'normal' canus.

The important features of the wing are:

- heinei has a deep black subterminal band on P5; canus only thin or broken band,
    broad black band on P5 on the left wing, a little narrower and almost broken on the right wing
- heinei has black all the way to PC on P8; canus only 50-75% of length,
    black on P8 almost reaches PC on outer web, on inner web about 85% of length
- heinei has black on P7 outer web more than 80% of length; canus less than 50%,
    black on P7 outer web hard to judge but I estimate about 75%
- heinei has long black 'bayonet' on P6 for approx. 65% of length; on canus mostly 20-40% of length,
    black 'bayonet' for just under 50% of length.

There's clearly too much wrong with this bird to claim it as heinei but equally it seems to show features at odds with a 'normal' canus. Perhaps the best that can be said is that the darkness of the mantle and some features of the primaries indicate a possible canus-heinei intergrade. Once I've had a chance to read the DB paper I'll come back to this.

Thanks to Mike Langman and others who've already commented on photos posted on the twitter. More opinions welcome as ever.

 * Larus canus heinei breeds in Russia from Moscow area east to Lena River in central Siberia; it winters in SE Europe, Black and Caspian Seas, also China and Japan.

2 comments:

  1. Great bit of research Tim and links too, thanks. Can't add anymore I think you've covered it. look forward to you nailing a classic heinei.. It is always good to see your great photos and educational deliberations.

    ReplyDelete