2nd year (apparent) Kumlien’s Gull Larus glaucoides kumlieni
Hidden Lake Park, Milpitas, California: 07 March 2005

For more photos (taken on 24th Feb) and further discussion on this bird have a look also at Les Chibana’s excellent BirdNutz Photos.

 

 

2nd year Glaucous-winged Gull (foreground), 2nd year (apparent) Kumlien’s Gull (center), adult Ring-billed Gull (rear)

 

2nd year (apparent) Kumlien’s Gull (center), with Thayers Gulls

 

2nd year (apparent) Kumlien’s Gull (left), with Thayers Gull

 

2nd year (apparent) Kumlien’s Gull (left), with Thayers Gull

 

 

 

 

1st winter Thayer’s Gull (with 1st w Glaucous-winged Gull behind), Milpitas, 07 March 2005

1st winter Thayer’s Gull, Milpitas, 07 March 2005

After I posted these images I put a message on Surfbirds.com linking this page and asking for any comments on this bird (and on “Kumlien’s Gull” in general) - the hits on this page quadrupled the following day, but no-one ventured a comment.

Perhaps simply “asking for comments” was a little too vague - but I suspect that the real problem is that the taxonomy of Kumlien’s Gull is so uncertain that commenting is a bit of a risk: why put yourself out there when there are so many snipers waiting to shoot your head off?

Hats off then to Richard Millington of Birding World who wrote a well-researched short article in BW Volume 18 Number 2. Richard’s article looked first at the historical treatment of Kumlien’s as a Nearctic subspecies of Iceland Gull Larus glaucoides and then at the suggestion made in 1925 by the American Jonathan Dwight that it is actually derived from hybidising Iceland and Thayer’s Gulls L. thayeri (the latter itself once regarded as a race of Herring Gull)…

So far, so well-known - but the article goes on to shed light on what is called a “hybrid swarm”, which is where things get very interesting. Apparently some bird species hybridise so extensively and so successfully that they produce self-perpetuating hybrid swarms - hybrids that breed with hybrids to produce further generations of viable hybrids with no negative selection pressures. Gulls appear to be very good at this sort of thing, and in the case of glaucoides and thayeri the resultant Kumlien’s “swarm” has been expanding eastwards out from the original range of Thayer’s Gull into the range of Iceland Gull so rapidly that Kumlien’s now probably outnumbers Thayer’s by two to one (though glaucoides is still far more numerous than either kumlieni and thayeri combined).

What this could mean is that, in time, the hybrid could actually replace one of the parent species altogether! What it means for identification is somewhat mind-boggling - unless every hybrid resembles every other hybrid how can there be a set of stable characters that we can use?

To further complicate matters, Richard’s article then adds that Icelands and Thayer’s may now be hybridising to the north of the range of Kumlien’s and producing first-generation hybrids that may resemble the “hybrid swarm” - or may not. Presumably these “new” hybrids could then breed freely with members of the original “swarm”, with so far unknown results.

I’m not a biologist or a taxonomist, but my question is this: from the point of view of the average birder are out-of-range individuals like the ones pictured below ever actually identifiable with any certainty? (And in asking it, perhaps I’ve answered my earlier ponderings about why no-one at Surfbirds posted a comment about the identity of the “Milpitas Kumlien’s”…)

Comments would be welcome, of course…

All photographs © Charlie Moores