Yellow-legged Gull pretending to be an American Herring Gull (Larus smithsonianus)

I checked Facebook's Western Palearctic Gull Group this morning to see if I had any comments on a selection of photos I had posted. Staring back at me was a gull that I was very familiar with and it was captioned as an American Herring Gull (Larus smithsonianus). I knew when I saw it back in November that it was something interesting, but I could not put a name to it.

After my holiday I uploaded pictures of the gull to the Facebook group and asked for opinions. I felt that if it was the default species, Yellow-legged Gull (larus michahellis), then it was a very untypical one. The first answer I received was that it was a typical Yellow-legged Gull. Alex Boldrini from Italy suggested it was a Herring Gull, so well done to him. However, the fact it appeared to have yellowish legs pushed the general opinion to Yellow-legged Gull. Alex and I argued that it was not a typical Yellow-legged Gull, but we were shown some examples of so called similar gulls. Alex argued that they were not actually matches, but the thread dried up and we all moved on.

Well yesterday Peter Adriaens and two others were at the Portimao Fish Harbour and they independently found the same gull. They identified it as an American herring Gull.

Putative American Herring Gull, November 12th 2016, Portimao Fish Harbour

The key to the identification is only seen when the gull is observed in flight from above or during a wing flap whilst preening. The secondaries show black markings rather than vermiculations, which are shown by Old World Herring Gulls. This is perhaps something I should have known, but it just hadn't stuck in my head, probably because I hadn't seen one before. Its quite tough to learn about something you are unable to experience. The greenish tinge to the bill is said to be good for AHG and the black markings on the tertials are also a helpful feature. I have quickly learnt about these features, but things are always easier when someone points you in the right direction.

It was quite docile when I saw it and was hanging about on 'Death Row'. This is an area at the harbour where sick or injured gulls tend to congregate. As such it walked away rather than flew, so I didn't capture any flight images. 

Putative American Herring Gull, November 12th 2016, Portimao Fish Harbour

Putative American Herring Gull, November 12th 2016, Portimao Fish Harbour

Putative American Herring Gull, November 12th 2016, Portimao Fish Harbour

Putative American Herring Gull, November 17th 2016, Portimao Fish Harbour

I had no idea the complexities of gull identification when I began this journey, but I am having great fun learning.

Update: since this post our bird has become the most discussed gull on facebook. Some now think it is probably a sick Yellow-legged Gull. Incidentally this was the view I took after finding it in November 2016. It returned to Portimao as a fourth-winter and its primary pattern, according to American gull enthusiasts, does not match any AHGs. However, both myself and other observers in Portugal have not seen a lusitanius Yellow-legged Gull that matches this one. The head streaking for one thing does not match any third-winters birds I've seen in Portugal. We wait its capture and DNA test if anyone is up for the challenge.

Second update: it has apparently been tested and its DNA fits YLG. The oddest looking YLG, but there you go.