Pacific diver at Caolas beag

Caolas beag is the straight between Longa island and the mainland at the northern end of the entrance to Loch Gairloch in North West Scotland. Eight days ago an adult winter plumage Pacific diver was found in the straight, loosely associating with black-throated divers and sometimes shags. It was reported for about five days but then nothing, no news either way. I wasn't completely surprised by this, Caolas beag is a long way from anywhere, even Inverness is a two hour drive, and Pacific divers aren't that rare these days, so it was unlikely to draw a big crowd. I did however expect a few birders today given that it's weekend and it's still a mega rarity in Scotland, with most UK records coming from England and Wales, so I thought that a few Scottish birders might be looking to add it to their Scottish lists. Be that as it may, I was the only birder on site this afternoon.

Tor Olson, who found the first Pacific diver for Norway, has kindly allowed me to use some of his photos here to better illustrate some of the identification features that I'll be discussing in this post. Note that his bird was a 1st summer bird whereas the Big Sand bird is being described as a winter plumage adult, though exactly what the differences are and if they would even be discernible at any distance I'm not sure.

Caolas beag is a place I know well from previous visits to this area. I'm not exactly local at the moment, but I am staying at Aultbea, a village about 17 miles away, so it was no trouble to visit this wonderful site today. 

Pacific diver (left) with black-throated diver,
Lista, Norway 12th July 2015 
Photo © Tor Olson

I scanned the water several times before I picked it up, quite distant with a flock of 12 breeding plumage black-throated divers. It had a completely different jizz to its cousins, being obviously smaller with a finer, shorter bill and a rounder head shape. The difference was so stark that it actually looked like a grebe swimming amongst the divers, as is shown well in this photo by Tor Olson.

Pacific diver, Lista, Norway 12th July 2015
Photo © Tor Olson

Crucially, it did not have the white flanks of black-throated which is a diagnostic feature of Pacific. It's face also lacked the the white cheeks of non-breeding black-throated and the overall impression at that distance was of  a bird with a grey head and  pale throat rather than the usual grey head and pale face of black-throated. It obviously stood out being the only non-breeding plumage bird in the flock.

Pacific diver, Lista, Norway 12th July 2015
Photo © Tor Olson

Obviously there is variation amongst individuals, perhaps even sexual dimorphism, but the overall size, head shape and bill size was quite different from the accompanying black-throats. I had no doubts that it was indeed a Pacific diver, even though it was much to far away to see the chin strap, which by the way is not diagnostic of Pacific diver because a proportion of black-throated divers also show this feature, as you can see in the photo below which I took on Barra in October 2023. 

Black-throated diver with complete chin strap, 
Barra 2023.

It was quite a sunny afternoon and as the sun moved round to the west viewing became more difficult and the birds more silhouetted, so at that distance there was no chance of a photo. I'll try again tomorrow morning.

Also on the straight today, at least four great northern divers, including a breeding plumage adult, and four breeding plumage red-throated divers.

I'd parked at Sands camp site cafe so the only decent thing to do was to retire there for a cup of tea and a scone. It was a pleasant afternoon so I sat outside on one of the benches and was rewarded with three white-tailed eagles in the air together for a while, before one broke away and flew right over my head!

The Pacific diver was my second, the first was a 1st winter bird in Northumberland in 2017 which it's safe to say showed a lot better! Even though that bird was a different age, the overall jizz of the species is clear in this photo. Dark flanks, shorter, finer bill, round head shape and dark cheeks. 

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