Thayer’s Gull

There has been much excitement in recent days at Blashford Lakes over the sighting of a potential Thayer’s gull. I say potential because these are not easy birds to identify or at least it is not easy to know exactly what you are looking at. Larger gulls are a particularly tricky bunch, they can vary quite a lot within species and not much at all between species and (even worse) sometimes hybridise!

So how do you ever know what you are looking at? For all the species there are the “Classic” birds, the ones that look like the have just stepped off the pages of the field guide, these should not be too difficult, although some genetic studies suggest even some of these might not be quiet what they seem. The others are more problematic, at least for people who like to put a name to them. Often it then comes down to looking at the various characters and scoring what is positive and what negative, after that you can consult experts or, for the more free-wheeling just decide if you are happy or not. For some there is no “right” answer, just the balance of probability.

So is this Thayer’s gull the real thing? The short answer is I don’t know and it will probably get decided by committee in the end and some will accept the decision and others not. Having seen the bird at some distance last night and then rather better tonight I have a few observations. The books often say they are structurally like Iceland gull and a claimed one I saw many years ago in Ireland was, to my eyes, identical in structure to Iceland gulls nearby. This bird looks bulkier than what I would expect for an Iceland gull, but it has the same wide, round head so typical of that species. Iceland gulls do have broader bodies and heads than herring gulls but this bird looks very heavy indeed. The wings do not look long and the rear of the bird on the water looks less attenuated than typical for Iceland, but this may be due to the rather large body size and males gulls are often a lot larger than females. As far as I can tell the plumage looks as though it has all the expected features.

Whatever it is, it is interesting and different from any other gull I have seen before, even the other one claimed as Thayer’s. It is quite obvious in the roost, it certainly stands out as different. Another way of looking at it is what might it be if it is not a Thayer’s gull? It seems American herring gull will hybridise with Thayer’s gull and that they will also hybridise with Glaucous-winged gull producing offspring that look like Thayer’s gulls. However it seems that these various hybrids tend not to have the round head, which this bird certainly does have.

If you are a bird lister it really matters if this is or is not a Thayer’s gull, importantly if it is accepted as such by the rarities committee once they have weighed up the pros and cons. Whatever they decide it is a very interesting bird and I am pleased I have seen it, I have looked at many, many thousands of gulls and never seen one quiet like it before. There is a school of thought that Thayer’s gull is just a form of Iceland gull and not a full species at all.

All this begs the question of just what defines a species, actually an important question for conservationists as rarity often drives much funding and conservation effort. A rare species will attract more effort than attract more effort than a sub-species. The definition of a species is  not a simple thing and not as clear as you might think and subject to change. Actually what matters are populations, we need to conserve populations, it does not really matter if they are species, sub-species or separate groups of one species. Keeping populations viable ensures their survival whatever their status, we should not consider them less because they are not a separate species by the current definition.

As for the Thayer’s gull, I enjoyed seeing it whatever it is eventually decided to be. Come to that I enjoyed seeing all the other gulls in the roost too. All 9,000 or so of them, including a juvenile Iceland gull, yellow-legged gulls, Mediterranean gulls and the thousands of lesser black-backed gulls and black-headed gulls. If you are interested there are pictures of the Thayer’s gull on the HOS go birding website, mine are so bad I will not torture you with them!

Elsewhere, away from the gulls, “Walter” the great white egret was on Ivy Lake and 2 black-necked grebe on Ibsley Water along with a single Bewick’s swan, a  real rarity here these days, although there were almost 200 wintering in the valley a few decades ago.