Something From Nothing

This post is simply a description of the Caspian Gull at West Bexington just over three weeks ago. I thought it might be useful as an example of what it is possible to extract from a rubbish video. Instead of fumbling around with a camera I could have spent another couple of minutes with the scope and then from memory tried to write a description in the field notebook which I don't carry these days, desperately trying to shelter the imaginary pages from the foul weather. But I didn't. I got some jumpy footage instead. I know which I prefer, and I can guess which is easier for a county records committee to assess...

2nd-winter Caspian Gull

Date: 26th January, 2020
Location: West Bexington, Dorset
Conditions: Very strong SW, steady rain, air full of fine spray. Dull and overcast.
Distance from bird: Probably 100-150m
Time: Shortly before 14:00. The bird was in view for several minutes, but probably less than ten.
Other observers: None.
Previous experience: As of 26th Jan 2020, 14 previous Caspian Gulls (11x1W, 1x1S/2W, 2x2W), all on the Axe Estuary, Seaton, Devon; all photographed. My first was a 2W in October 2007.

Initially picked up on the West Bex mere with bins (Zeiss Dialyt 10x40 BGAT) it was the clean white head and breast which caught my eye, belonging as they did to an obviously immature bird. I realised it was a candidate for 2w Caspian Gull, and scope views (Nikon ED82A 25-75x zoom) confirmed. After loafing on the mere with other gulls for several minutes, the bird lifted off and flew into the wind, over the beach and away.

Despite awful weather I really wanted some images, and recorded 1'50" of video on my Nikon Coolpix P900. The video is available here. The following stills are taken from that recording, and illustrate various ID features, as highlighted in annotations or text...

Photo 1

Photo 2

Photo 2 shows complete, narrow black tailband, and clean white underparts.

Photo 3

Photo 3 also shows dark secondaries. This, plus the complete, narrow tail band definitely rules out 3rd-winter Herring Gull. While I was watching the bird I couldn't remember exactly what HG of this age would look like, so it was a niggling worry at the time. However, 3W HG would have grey, adult-type secondaries with white trailing edge, and just traces of tail band.

Photo 4

Photo 5

Most 2W Caspian Gulls carry a small mirror in p10, and Photo 5 depicts it clearly. Through the scope it was surprisingly easy to see this feature on the open wing, mainly from below because p9 largely masks p10 from above.

The combination of features shown by this bird rules out Herring Gull. It cannot be HG in 3W plumage for reasons outlined above, and 2W HG would not look as clean white on head, breast, belly and underwing. Neither would it be this advanced in moult on the scapulars (usually few grey feathers, if any) and coverts (again, few grey ones) and its tail would have a wider, less sharply-defined terminal band. According to Gibbins et al (2010) a p10 mirror is shown by 1-5% of 2W HGs (particularly argentatus) so any 2W bird which has this feature is far more likely to be a Casp. In addition, there were no anomolous features which might suggest a hybrid origin.

Finally, it is helpful to compare the photos above with the bird in the following image. This 2W Casp was seen in Torbay in November 2015, and three days later on the Axe Estuary, Seaton. Note similar state of moult in scaps, coverts and tertials, the bill pattern, whiteness of head and underparts, and spotted 'shawl' on nape. It all matches the West Bex bird extremely well.

2W Caspian Gull, November 2015
Top: Torbay, Devon (photo: Mike Langman)
Bottom: Axe Estuary, Devon (photo: Ian McLean)

References: Gibbins et al (2010) - Identification of Caspian Gull Part 1 (BB 2010)


Here endeth the description. I realise this kind of post is a bit..er...'specialist', and if you have reached this paragraph after wading through the rest of it I do hope the above was helpful. If I am jammy enough to find interesting birds in the future I might well do it again.