Saturday, 10 December 2016

American Herring Gull at Portimão

How many bird species have you seen?  How long is your life list?  Whatever your answer, these days it will need to be qualified – you will have to make clear which checklist it is that you are working from.  Taxonomy definitely isn’t an exact science, it’s very much a matter of opinion and when it comes to lists of the world’s birds, there are quite a few versions to choose from.

It doesn’t seem so very long ago that the number of bird species in the world was reckoned to be about 8,500.  Now, according to BirdLife International there might be as many as 11,000 but different authorities have differing totals and they are changing all the time.

As our knowledge of birds increases so we learn about the differences between them, how they look, how they sound and how they differ in their DNA.  How much do they need to differ before we regard them as separate species?  Well, that really is the big question and why it is that we are faced with a choice of checklists and why there are differing totals.  Simply, there is no agreement on the matter, no standard to be reached. 

A case in point this week has been a bird here in the Algarve that is treated as a separate species, Larus smithsonianus, by BirdLife International, the British Ornithologists Union and most others but is still regarded by the American Ornithologists’ Union only as a subspecies, Larus argentatus smithsonianus.  It is, variously known in English as American Herring Gull, Arctic Herring Gull or even Smithsonian Gull and in Portuguese as Gaivota-prateada-americana.

Although previously regarded (still by the AOU) as a subspecies of European Herring Gull, we are told that DNA studies show smithsonianus to be more closely related to California Gull, Iceland Gull and Glaucous Gull.  Who would have thought that?

It was found at the ‘docapesca’ (fishing dock) at Portimão last Sunday.  It seems to be only the second occurrence of this taxon in the Algarve and as such it attracted a small number of admirers during the following days.  It appears to be a bird that is in its fourth winter, close to being full adult.  Those who found and identified it did very well as the plumage features aren’t particularly striking when seen amongst the many and varied gulls that gather at this site.  The streaking on the head, neck and sides of the breast and the various dark markings in the wings are all pointers as are the pale eye colour, the pink legs and the bill pattern.

There doesn't seem to be any doubt that this bird is distinctive enough to be called smithsonianus.  However, whether smithsonianus is different enough to be regarded as a separate species is still open to debate.  It probably depends on whether, by nature, you are ‘a splitter’ or ‘a lumper’.

No comments: