So Thayer’s has gone, reduced to a footnote in the taxonomic listings and not even afforded sub-specific status like Larus glaucoides glaucoides and Larus glaucoides kumlieni. I would really like that situation explaining as, to me a simple birder, it would have been logical to retain thayeri for simple recording purposes (always handy should there be future research), even if we can’t have just Larus and have to have it with Larus glaucoides in front of it.
The rationale for the lump seems to be that they (Thayer’s) have been found breeding with Iceland Gulls, well Kumlien’s Gulls actually as it is unlikely, but not impossible, that a Thayer’s and an Iceland would meet anywhere other than the winter feeding battleground of dumps, sewage outflows and fish processing plant waste pipes, long may they remain unregulated! I had always thought that interbreeding was not necessarily a barrier to full species status, if it was, surely we’d be rather reduced in species to say ‘Duck’ for all those anatidae that like to throw their darvic rings onto the table and take home something a little different. I also wonder how hard they looked for the definition of the interbreeding zone. I don’t know what the percentage of mixed pairs in the breeding range would need to be before the species pair became true but, presumably there are pure Thayer’s that only breed with pure Thayer’s so isn’t that a species?
I think, and I’ve said this before, the definition, no make that re-definition of Thayer’s Gull should have been considered before lumping. What makes a gull a Thayer’s, what suite of plumage and structural characteristics are required before you can ink it in? And why did we keep stretching the identification criteria to fit the bird? Now the lump has congealed, we will have thousands of good Thayer’s records that will only make eBird as Iceland Gull, each Thayer’s something of a missed opportunity to define a core range and the limits of dispersal and vagrancy. I suppose I could list again what I think makes a Thayer’s but you already know anyway, you are not the sort of birder to let a degree of difficulty stop you working out what you are seeing, why you can even identify silent Trail’s most of the time, just by looking at them!
I think that we in the field who look at gulls will keep on looking for Thayer’s in season, and probably calling them same in the privacy of our own Excel files. The lumpers and splitters on whatever committee is busy with such activities will still prevaricate endlessly, but most will largely ignore them and make the ID of those obvious, if shop-soiled species anyway, in much the same way that we do with Mew Gull (four species), Fox Sparrow (another four) and don’t forget Willets, eastern and western although I think we’d be better getting away from geographically orientated monikers and move to something more distinctive and accurate, Big Willet and Little Willet comes to mind.
Putting Thayer’s to bed, for now at least, here are a few shots – starting with the 2017 Pubnico bird found by Alix that also visited CSI; going through to pale end Kumlien’s. Remember, these are all Iceland Gulls right!