I’m not one for sitting in an office, so luckily for me, most winters I’m fortunate enough to get away from my desk and spend some time doing seabird and cetacean surveys on a variety of fisheries vessels. During the early winter of 2015, I was on board the G.O Sars, a Norwegian vessel that was sampling groundfish as part of the ongoing International Bottom Trawl Survey. While it’s a very comfortable boat to work from, it (along with all other fisheries vessels) comes with the huge disadvantage that it attracts a lot of birds – which can have a rather disruptive effect on a seabird survey! Most often, this disruption takes the form of the sheer volume of ‘ship associates’, making surveillance difficult, but it can also be a little distracting when a white winged gull ghosts by at eye level and at a few metres range. Events on February 6th proved to be one of the sterner tests of my ability to focus on the survey that I’ve ever faced.

 

Having had a few days in Lerwick at the beginning of the month for a crew change, we had left Shetland with the intention of sampling stations up the eastern coast of the islands before heading back towards Norway.  As we steamed westward from a sampling station our survey was in full swing and I was doing my best to observe through the halo of gulls, fulmars and gannets we’d attracted. Despite my efforts, my attention was grabbed for a split second when a strikingly white headed and pale tailed gull swept past me. On its next pass I got much better views (I was ready for it!) and noted the dark wings, neat black tail band, and pale grey mantle. I knew I was onto something that would be pretty unusual as far north as Shetland, so on its next pass I was ready with the camera. Luckily I got on it quickly and managed to get some reasonable record shots.

 

My thoughts at that point were that it was either a yellow-legged or a Caspian gull, and initially I was favouring the former, with that opinion strongly biased by the fact that they’d been recorded in Shetland before. I quickly checked with the officer on watch who confirmed that we were well within UK waters, and took a note of our position. After that I swapped roles with the other surveyor, allowing me a little more time to look out for the bird. After about ten more minutes the bird had failed to show again, so I began to look through the photos.

 

Again, the white head and tail struck me as the most obvious features, especially as they contrasted with the rather dark upperwings, However, the photos also shed light on a few other features that swayed me away from the idea of a yellow-legged gull. Adding to the dark winged effect were plain, unpatterned greater coverts (apart from paler tips) and a strong band of black formed by the tips of the secondaries. The all dark bill seemed long, and with very little gonydeal angle to speak of. Crucially, on one of the images, I’d managed to capture a pale underwing, and on those where the bird was viewed from above, a neat ‘streaky boa’ effect was visible on the hindneck. It didn’t half look like a Caspian gull.

 

The bird remained out of view for a while, presumably having disappeared into the melee of gulls that were following the boat, which allowed us to fully focus on the survey for the next hour or so. As the light began to close in during the mid afternoon, we arrived at our next sampling station and I disengaged the survey brain and set about relocating the gull. It didn’t take long, as the bird soon drifted over the back of the vessel, and a couple of passes later it did the extremely decent thing and landed on the back of the boat! It stayed here until dusk, which gave me plenty of time to assess its features and absorb it’s rather unique leggy, long winged jizz.

 

Identification in detail

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Annotated versions of the following three photographs were supplied as part of the description sent to SBRC and Shetland Bird Club rarities committee, which was accepted by SBRC in June 2015. I’ve tried to summarise the key features in each of the photos focussing on those that were the most striking in the field, and those that really helped clinch the identification.

 

Picture 1.

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Picture one was taken through the window of the bridge, and represents the best of many efforts to record the bird on either its second or third pass, after the initial sighting. Here the strikingly pale head is obvious, along with the pale and relatively unmarked tail with its neat black terminal band. The wings appear uniform brown with a pale grey mantle, which in combination, gives a neat impression of a ‘four colour gull’ (black, brown, grey and white). On close inspection, the pale back is comprised of silvery mantle and scapular feathers, some of which are weakly marked with diffuse shaft streaks and subterminal bars. All other large white headed gulls of this age would show much coarser patterning here, which would make the mantle and scapulars appear darker, showing less contrast with the wing. The coverts are mid brown and appear unmarked apart from paler tips to the greater coverts, which forms a diffuse pale bar, contrasting strongly with the almost black secondaries. The rather uniform brown colouration across all of the coverts helps to age the bird as a 1st winter/2nd calendar year bird, as a 2nd winter would be likely to show some pale grey coverts. The inner primaries are slightly paler, and the pale spots in the outer webs of Ps 2 – 4 are a good feature for Caspian gull. The bird appeared pretty large and bulky in flight compared to the herring gulls present, and this, in combination with the white head and tail, gave the bird a rather 1st winter great black-backed gull-like feel.

 

Picture 2.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Picture 2 was taken around 3:30 pm, a few hours after the original sighting. Again, the picture shows a neat, ‘four colour’ gull and here the paleness of the underparts is obvious. Also, the tertials are clearly visible here and are dark and largely unmarked, with very neat pale ‘thumbnail’ tips. The ‘streaky boa’, a classic feature in immature Caspian gull, is also prominent. This photograph also nicely illustrates some of the key features of Caspian gull jizz. The legs are rather thin, and long (a part of the birds foot is visible just below the railing, helping judge leg length), the wings are long, and the head is small and pear shaped, making it look a little ‘snouty’. The bill is dark, narrow and parallel sided, with only a very weak gonydeal angle. The rear end looks attenuated (owing to long wings) with a characteristic ‘ventral bulge’ behind the legs. All of these features contributed do a more delicate yet rangy feel, when compared to the more compact looking herring gull, despite the fact that this bird was larger than many of the herring gulls it was directly compared with.

 

Picture 3.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Picture three is included here as it shows the pale underwings, another good Caspian gull feature, as well as rather nicely illustrating the dark eye, pale head, ‘streaky boa’, and bill structure.

 

Discussion

 

The bird remained with the vessel until dark, but was not seen the following day, despite possibly roosting on board (it was last seen perched on a railing, lit up by the vessels safety lighting). Turnover rates of ship-following gulls are difficult to get a handle on, but some distinctively plumaged individual gulls have been noted attending IBTS vessels for eight consecutive days, and as such I was a little surprised that the bird was not seen again the following day. There were plenty of other fishing boats in the area, all of which would have had a greater lure to a scavenging gull than our scientific research vessel, whose samples would have been a tiny fraction of what some of the commercial vessels nearby would have been landing. As such it’s possible that the bird latched on to a different vessel nearby, or at least abandoned our vessel as we headed westward into less productive waters. We certainly noted many fewer ‘ship associates’ the next morning, suggesting an exodus at some point during the night. Unfortunately, despite some searching, it did not make its way to ‘the Catch’ in Lerwick, to many people’s disappointment!

 

While the identification of this bird was relatively straightforward, my lack of experience of this taxa, along with our position at the time made me a little exercise a little caution, so I emailed a selection of images to birders with more experience of cachinnans to confirm the identification. Later in the evening I began to receive positive replies, but it wasn’t until I posted a few pictures up on Facebook that the idea that this could be a first for Shetland was suggested. Our position at the time of first sighting was 60 30 033 N, 000 47 019 E, which, using a measuring tool in google maps, translates to a distance of approximately 85 km or 52 miles, just a few degrees north of due east of Out Skerries. ‘At sea’ records of Wilson’s petrel and Fea’s/Zino’s petrels have been accepted onto the Shetland list, which sets a precedent allowing the addition of this species onto the county avifauna as well.

 

Figure 1. Position of the initial sighting (red marker), with distance measured at 82.26 km from Out Skerries. Screengrab taken from Google maps.

 

Other Scottish records, and geographical context

 

Caspian gull was admitted to the Scottish list relatively recently, with the first bird at Belhaven, Lothian, late in 2006 (appearing just too late for the species to appear in ‘Birds of Scotland’). Including the Shetland bird, there have been six more accepted records of this species since the first one. There is a distinct east coast bias to records, with a cluster of three around well watched sites east of Edinburgh, and others from Peterhead and the Montrose basin. However, there is one record from Strathclyde Country Park, and one was in the Loch Gilp area of Argyll at around the same time as the Shetland bird. Over the border, the species has been recorded just a couple of times in Northumberland but not in Cumbria. The UK strongholds for Caspian gull appear to be the Midlands and the South East of England. Caspain gulls are rare at this latitude anywhere around the western edge of their range, but there are recent records from Iceland, and a record from Bergen, at an almost identical latitude as this record, from early winter 2013.

 

Of the accepted records, five have been from mid winter (December – February) and two from October, mirroring the patterns of occurrence in parts of the UK where this species is more regular.

 

The next Caspian gull in Shetland

 

I must admit to feeling slightly sheepish about being found by a first for Shetland (I see it very much in those terms!), especially when the only other people who got to see it were my co-surveyor, and a few Norwegian fisheries scientists who were pretty unimpressed with the whole affair. While undoubtedly Caspian gulls will remain rare birds in northern Scotland hopefully, it won’t be too long before the next one. The Catch, and the boats returning to it full of fish, act as a magnet to gulls, and being located on a North Sea coast is a potential plus in terms of the distribution of previous Scottish Caspian gull records. Their mid winter peak would coincide nicely with the period that the gulls in the area are likely to be receiving the most attention and in addition, the ready source of food must mean that gulls are likely to linger in the area, making them more likely to be detected. I sincerely hope that Shetland birders get a better chance to catch up with this largely southern species sooner rather than later. Good luck finding it!