If you are not interested in the finer points of Gull identification, feel free not to read this post.  I won’t mind.  There is no hidden message in this post, no flourish at the end, not even a piss poor pun to reward your dedication at the end of all the discourse on primary feather configuration.

For those that have decided to commit, here goes – it’s like the Yarmouth Pleasure Beach in ornithological form!

The irregular reader will have been aware that a Yellow-legged Gull Larus micahellis had been found in the patch, and that its image had appeared on this here blog.  Not a quality image, but with notes taken the identification was reasonably certain.  I didn’t think that it would hang around, and there is no shortage of gulls around here to aid distraction/confusion.  Nonetheless, it is still knocking about and it is still seemingly paired up with a Herring Gull.  I don’t know who is Martha, who Arthur.  Neither bird is obviously bigger than the other.   But, because it is still around and still paired up, I wondered if the Gull with yellow legs might be a Herring Gull sub-species as this would make the pairing more likely.  Actually I didn’t really but thought that at the very least, it would be interesting to go through the process of making sure. 

I had heard tell of these beasts referred to as omissus.  So, I had a look in the big-scary-gull-book to find out the finer details of this omissus thing, and started with the index.  It isn’t there.  No really.  I read every single word in the index of that book, and omissus isn’t there.   It is on the web, this link for example, but no reference to it in the index of the Gullists bible.  I did eventually find reference to it on page 263.  Omissus is an occasionally used name for birds that populat(ed) the Baltic Sea.  But it’s not that simple.  All round the Baltic States and Southern Finland it turns out that Herring Gulls often have yellow legs, and can have orbital rings and primary tip markings that can confuse the unwary, albeit this is often going hand in hand with a paler mantle.  So rather than carry on with the possibility that I could end up sobbing in the corner with little nuances of the Kodak Grey Scale going around my head, I thought I’d attack it from the other side.  Definitive proof of ‘micahellisness’.

Ready for a picture yet?

yes, I know about the fence


To do carry out this ID quest, of course, requires better pictures.  And pictures of the open wings, nothing else will do.   No gull ID can be 100% these days without decent images of the primaries.

Check it out.

yes, the fence again. I know


So we have a picture of a darker mantled gull with yellow legs and its wings open.  What do we need to see?  It’s  all about P5, innit.  From Malling, Olsen and Larsson –  “unlike typical Herring, black markings solid on P5”  and “Shows extensive black subterminal bar on P5; if present in Herring it is narrower and mainly restricted to outer web”.  Which looks like this.

from the left...

 Also note “white mirror on p10 and small white mirror on P9” which points to western rather than eastern population origin.

So, as far as I know, by the book it is a Yellow-legged Gull, but the P5 on the link at the beginning looks much the same.  Which is stated with confidence as an omissus.  Bollocks, I’ve done what I didn’t want to do and argued myself into a self-created corner.  Based on the P5 argument, one of us has to be wrong – or am I missing something?

I’ll have to get to watch it some more, take more photos and read some more. 

Either way, as I stated previously, it might be about to breed with a Herring Gull.  You thought this post was dull.  Wait until the young start getting in reach of the camera!

1 thought on “ooo-missus!

  1. I have no specialist gull knowledge to pass on, however I have sent you a message with part of a paper from British Birds, my favourite bit about omissus is “Herring Gulls with yellow legs seen in Britain have been (and sometimes still are) referred to as L. a. ‘omissus’: something we emphasise should cease”. If you didn’t know, a pair of gulls bred at Yarmouth last year that were ID’d as a Yellow-legged and a Herring x Lesser Black-backed (hmm, I wonder what that hybrid would look like…), some small photos can be seen here:

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