This blog is about my birding exploits, which mainly take place in the Weymouth/Portland area, in Dorset. Will also include stuff from elsewhere, plus some other critters too. Hope you enjoy. All photographs are © Brett Spencer, unless indicated otherwise. The above image is of a Siberian Rubythroat, taken in Holland in 2016.

Friday, 31 January 2014

Argentatus Revisited

 Thought it was timely to review this winters Scandinavian Herring Gull sightings at Radipole Lake. First off, this is a rare bird locally and when it comes to 1st-years, we're on a steep learning curve with these things. Every so often, mistakes will be made, but that's what makes learning about the field identification about these things more interesting. Since 1990 I've observed possibly 35+ individuals, although duplication may mean this figure is less. Most of these have been adults or near adults, with 2 3rd-years, 1 2nd-year and 4 1st-years also being observed. Extreme dates have been 31st October and 3rd March. The best year locally was 1995 when I saw about a dozen individuals, all adults or near adults and 1 3rd-year, this was mainly because of Russian fishing factory ships stationed in Weymouth Bay. Since 2000 they have become a lot rarer and I have only encountered 8 since that year, 4 adults and 4 1st-years. One thing that I am aware of is that we are overlooking 1st-years, as this age group should be, in theory, the most common age group locally, as 1st-year gulls tend to move further afield than adults.

This was the first 1st-year Scandinavian Herring Gull I ever saw at Radipole Lake 24th Dec 2011. I was struck by it's distinctiveness and by using a combination of features, the most obvious individuals can be claimed as showing characteristics of this form.

Since then, I have seen odd birds that have shown some, but not all the requisite features and these are either within the range of our own local Herring Gulls or may be intergrades. Obviously, looking more closely at our own local Herring Gulls in order to try and find a Sandinavian bird, as well as looking at many images on the internet and doing some reading up on the subject has been very educational. So, let's look at this winters crop that are all 1st-years.

Image taken on 7th Dec 2013.

This is an oddly marked bird and could be an argentatus, but I do have reservations with a few things about this individual, notably it's tertial and bill pattern and it could conceivably be a Herring x Great Black-backed Gull hybrid as unlikely as that may seem. 

Image taken on 14th Dec 2013.

This was a distinctive bird and it's structure and various plumage features certainly put it in the argentatus camp, though it was a pale individual and had no retained juvenile scapulars. It's not a typical individual, but I consider it to be within the range of variation shown by argentatus.

Image taken on 19th Jan 2014.

This is a classic individual and there can be no doubts about this one.

But then, as part of the learning process....

This bird is thrown into the equation. Photographed on 25th Feb 2012. Note retained juvenile rear scapulars and snouty look to head and bill profile.

Just look at that bloody tail pattern. I have it on good authority that this is an example of a dark variant argentatus. 

It's certainly a scary one and not one I would have sorted out without an expert opinion.


Bomber said...

As ever, some perceptive and insightful work from Brett. Without doubt one of the most pre-eminent Dorset birders of our generation. I always learn something from this Blog.

Keith Pritchard said...

Might not the top bird (2013) have an unusually advanced scapular moult for mid-December / L.a.argentatus Brett? However, the idea of a Herring x Gbb is fascinating. Keep them coming, they can only drive us mad!