Saturday 13 December 2014

Another look at the advanced Third-winter Caspian Gull and a Puzzle

It was bloody freezing today at Shawell, but I felt it was my duty to keep the gulls company. Its not that often that you have to scrape the ice of your car windows during an afternoon, but that's what I had to do after finishing 'sea gulling'.

I managed to read the colour rings on five species of gull today, which may be a record for me at Shawell. The much hoped for white-winger didn't appear, so perhaps the 'weather bomb' has not fully exploded yet. The weather map earlier in the week looked great for pushing a few towards us but we'll have to be patient.

Since mid-October I have seen at least one Caspian Gull on each of my visits to Shawell, but today it looked as though I would be unsuccessful. Many gulls were out of site from my position, but after a bit of argy bargy amongst the gulls on the top of the bank I spotted the interesting regular third-winter lying down. It is interesting because it looks more like a fourth-winter: its tail still has most of the dark band, instead of a long white tip to its longest primary it has a large white mirror with a black tip to the feather and on the outstretched wing the black extends as far as the Alula. It could be a fourth-winter, but the extent of the black in the tail makes me feel more comfortable with third-winter.

Third-winter Caspian Gull

As normal there was a challenging gull. The one in the photos below looked like a Caspian Gull at times, but then it could look a little odd. It is often difficult to get a true reflection of what you see when looking through your scope compared to digiscoped photos. Its bill doesn't look as good as it did when I viewed it through my scope. Its plumage is most consistent with a fourth-winter, but it looked more adult like, but it did have lovely long spindly legs. 

To me it isn't quite pure because it just doesn't quite tick all the boxes.

Its primary pattern fits sub-adult, as P10 has a long white tip and black that is slightly more extensive than on a full adult, P5 has a black band across it that is wider on the outer side and P4 had a black spot on the outer side. If it is an adult then the primary pattern is that of a hybrid, but if its a fourth-winter then it could be OK. Easy isn't it. 

I'd be interested in any comments about the gull below, as trying to determine the borders of acceptability for this species is challenging. The trait scoring system only works with adults and first-winters. 


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