Ask any Shetland birder how many Black-throated Divers they have seen in the archipelago and it is quite likely to be so few that they could recount them all. Ask the same question of birds in summer plumage and the answer might barely be one! This is certainly the case for me – and only once ever have I had the chance to enjoy their full summer splendour here. Even back then, well over 10 years ago, the careful process of eliminating Pacific Diver (however unlikely a summer-plumaged bird might have felt at the time) was undertaken. Thinking back to that bird, nothing about its structure suggested anything other than Black-throated Diver …
That bird, the process and the first impressions it gave came right back to me when I picked up a summer-plumaged 'black-throated' diver through my bins off Brough Lodge, Fetlar, on 18 May 2023. I was in the process of facilitating 'scope views of a flock of five Common Scoter for the birding tour group that I was guiding. Stepping back to the 'scope and jumping the queue to view, I asked if I could reposition it onto the diver, my excitement already elevated at the thought of even a Black-throated. The bird was actively foraging, barely on the surface for 10-20 seconds at first, but working its way towards us approximately 300-400 m away from where we watched, at the road end by the old slipway.
In the 'scope, although my first view was brief, and its posture in active foraging mode the bill looked slim and disproportionally short for the head and overall body, much more similar in profile to Red-throated Diver as opposed to Great Northern Diver. A second, slightly longer view gave an even better impression to suggest a contender for Pacific.
The vertical white lines on the neck of Pacific Diver are narrower than the black ones, as seen in this photo. Furthermore, Black-throated average four to six white lines, with Pacific five to seven (Brydon Thomason).
I calmly explained to the group that I needed another couple of views of the bird as it might be better than a Black-throated. As I did so, my mind was going through the usual rollercoaster of rare-finding self-doubt, trying to rationalise it back to Black-throated. But no – by the third and fourth views it really was looking the part structurally and by now I also noted the bill to often be held more like Red-throated, slightly above horizontal (not level as in Black-throated), and so I fixated on looking at the flanks. Due to its active diving, this proved tricky, but it later transpired that this feature could be appropriately assessed with images downloaded.
I knew I needed photos so I dived into back of the minibus for my camera and fired off a few frames each time it surfaced, by now probably 200-300 m offshore, perhaps less. I was extremely grateful for a 45-megapixel camera and 500-mm lens! Even at about 80% crop, on the LCD screen the head and bill structure really did look the part for what I would have thought Pacific would look like – even though I'd never even seen one before.
Now, in any circumstance the possibility of such a bird and the process to go through is a high-octane situation, but when you have tour-leading responsibilities to six birding holiday participants, and with a 15-minute window before your ferry off island sails, this was next level! Time was pressing, but I knew I had one more ferry option. I needed help, ID literature and informed opinion – and quickly.
I consulted the identification guide I've found to be the most instructive and interactive of all in recent years: Dave Cooper! I fired through four shots of the bird on WhatsApp, without even an accompanying word, while still trying to get further views and make sure my group were all OK, which they certainly were – they were buzzing! They could see and feel the excitement and were absolutely enjoying being part of it all.
So far as identifying summer-plumage Pacific Diver, I could remember the obvious: a straight flank line (not showing the rear flank 'mud-guard' of Black-throated) and structure. But for the various supporting plumage features, such as cleaner/colder/whiter nape and the number and thickness of vertical neck stripes, I knew there was overlap. Because of its active feeding posture, with body slightly submerged, conclusive views of the flanks were not easy. I felt relatively sure I couldn’t see the diagnostic 'mud-guard' of Black-throated on the rear flanks. However, I could not be certain it wasn't there! The eagerly anticipated blue ticks appeared on my WhatsApp message to Dave so I wasted no time waiting for a reply, calling him immediately instead.
The rear head nape was distinctly cold, even whitish, rather than the typical of shade of grey-brown seen in Black-throated Diver (Brydon Thomason).
He agreed that structurally it looked really good for Pacific, and that by crazy coincidence, informed me that one had just been found off south-west Norway. As luck would have it, he was at home – which for Dave in May during daylight is a rare event in itself! This was exactly what I needed – someone to consult literature while I tried to tend to the group and get more views and photos.
I then also forwarded the same back-of-camera shots to Paul Harvey, who had been through this very same process with Shetland's first Pacific Diver in 2013, also a summer bird in spring.
I then called resident Fetlar birder Paul Macklam who, remarkably, was with me within 10 minutes. Paul had just a couple of 'scope views before a cargo ship sailing south through Colgrave Sound appeared to unsettle it, pushing it further north, and we lost it. He too agreed on its overall structure strongly favoured Pacific. By now we had made the group decision to book the later sailing off which gave us another 45 minutes and yet, despite our combined efforts, we did not see the diver again. In total we had barely 20 minutes from picking it up to losing it completely.
Meanwhile Dave was tremendous, cross-referencing plumage features, and sending photos of various papers and plates, showing pro-Pacific features that checked out with this bird, helping us confirm:
- The vertical white neck lines were much thinner than the black ones;
- Black-throated average four to six white lines, Pacific five to seven – this bird showed five;
- The rear head nape was distinctly colder, even whitish, rather than the typical of shade of grey-brown of Black-throated.
Additionally, he found a reference to how these neck lines tend to be 'disrupted at base' on Pacific, essentially branching off, whereas on Black-throated, they are straight, vertical and even. Again, this feature checked out.
Once I knew Paul had seen my message, I gave him a call. As expected, he really liked it structurally but worried for me that without being certain about flank detail, clinching it may be tricky, knowing that the supporting plumage features can all overlap. What Paul did encourage me to do was to put my thoughts and photos out on the local WhatsApp group as he had regretted not doing this sooner with the Grutness bird.
As we had a two-hour journey back to St Magnus Bay Hotel in Hillswick, I felt like this was a really good shout and appreciated the advice, while Dave continued to search for information online. For me, with tour-leading responsibilities my number one priority, continuing the ID process simply was not going to be possible until much later that evening.
The first response to my message was as speedy as it was informed, from Sam Viles at BirdGuides, who drew attention to a feature he could see this bird showed unequivocally, which I never even knew to look for, that had been referenced in a Birding Frontiers article on the Grutness bird in 2013.
Sam quoted a comment made by Keith Brockie: "The easiest way to separate arctica from pacifica is the extent of the white neck stripes. In pacifica the neck stripes end before the base of the black throat patch, look at any photos and it can be easily seen and to my knowledge has never been commented on!"
Unfortunately there was no sign of the Pacific Diver the following day (Brydon Thomason).
Keith, and Sam in this instance, were absolutely on the nail and based on this feature, aided by everything shown on my photos, it was upgraded nationally from 'probable' to 'mega' – all while we were still in transit! It is quite bizarre to think how poorly documented this feature is, which is perhaps better described as 'the base of the black throat patch forming a collar that separates the vertical neck and breast-side stripes'.
As I am always one to err on the side of caution, and even though it looked solid (especially given we hadn't found any mention of this apparently new feature elsewhere), I pinged the same WhatsApp content to Killian Mullarney for his thoughts, accompanied by an overview of the features we'd noted, the Keith Brockie quote and link to article. Killian's response was very positive and supportive of Pacific, even without the new feature (which he agreed, though it is hard to see at rest, when neck stretched upright, is indeed solid and reliable).
At last, almost four hours after the discovery, I was able to sit down to dinner with our tour guests and thank them for being so patient and understanding of the process and make a celebratory toast to Britain's twelfth and Shetland's second Pacific Diver – and only the second record of a summer-plumaged bird. The following day quite a few birders, local and visiting, made the journey to Fetlar and some continued to visit the site over the weekend, but there were no subsequent sightings.
We all say it time and time again: luck plays such a massive part in finding rare birds and this feels especially true here. But an even bigger part of the process that I always appreciate and enjoy is the input of others, whether present or remote – it's what birding is all about.
A massive shout-out to Dave Cooper (who pretty much spent the afternoon in books and online to help) and Sam Viles for being so quick off the mark in pointing out the 'new' feature, Paul Harvey for comments and advice, Killian Mullarney for his comments and support (and always making time to comment), Paul Macklam for joining us so promptly and, last but by no means least, our birding holiday participants for being so patient, understanding and encouraging.
It also feels appropriate here too to mention how special it was for such a big bird to find reference and answers on the Birding Frontiers blog, on pages and by people pulled together by the late Martin Garner, who would have been in his absolute element with this bird. The reliability of the 'neck collar' feature is testament to what Martin always championed – we are indeed, 'always discovering'.
- Visit shetlandnature.net for expert-led Shetland birding tours.