Friday, 1 November 2013

Azorean Gull Again

I'm still working through my gull photos from Portugal and researching the gull I consider to be an Azorean Gull. The experienced gull watchers that I've asked have either energetically or cautiously agreed with my ID. However,  a couple have suggested that it may have come from either Madeira or the Canaries rather than the Azores, as the Yellow-legged Gull populations from these islands can look the same as those from the Azores. I think this is a just in case remark. 

Photographic evidence appears to show more extensive head streaking on the Azores individuals and so my bird looks good as far as that's concerned. A single mirror on P10 only is more common amongst the Azores population rather than from the other islands - mine had just a single small mirror on P10 and no mirror on P9. The mantle shade/colour of my bird also fits Azorean best as far as I can determine.

Azores Gull, Portimao fishing Harbour, Portugal, October 1st 2013
Below is a comparison of four different gulls, including the Azorean, photographed around the same time. 

In clockwise order from top left: Yellow-legged Gull, my Azorean Gull, Channel Isles Lesser Black-backed Gull and a Scottish Lesser Black-backed Gull. Looking at these images it would appear that the mantle grey gets darker in that order. Yellow-legged Gull is said to have a Kodak Grey Scale value of 5 -7 , Azorean Gull 7-9 and Lesser Black-backed Gull 8-10.

In the close up image below of the mantles in the same order it would appear to agree, but there isn't that much difference between the Channel Isles Lesser Black-backed Gull and my Azorean Gull. This is unsurprising really as the Lesser Black-backed Gulls from the south and west of Britain are the palest of the species. The Kodak Grey Scale range of Lesser Black-backed Gull is 8-10 and Azorean Gull 7-9, so there is a good overlap. 

The photographic evidence is worth looking at, but in the field the mantle colour was clearly different  to the other gulls, which set it apart from the other species.

Azorean Gull L. m. atlantis

Some of the discussion about out of range Azorean Gull focuses on either hybrids or Yellow-legged Gulls from north west Spain. Well I've seen a few hybrid Lesser Black-backed Gull x Herring Gull and, although they have similar coloured mantles, they do not look like Azorean Gulls to me. As far as western Yellow-legged Gulls, well I saw plenty of wintering YLGs in Portugal including some with quite streaky heads, but none had the look of the gull that is the subject of this post. The one below had a fair amount of streaking on its head, but other than that it was a typical michahellis.

Yellow-legged Gull Larus michahellis

There appears to be plenty to learn about the gulls from the Atlantic islands, as much of what I've read points very much to a work in progress.

Click Here to read one of the reference papers.

Chocks Away
Azorean Gull

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