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.
It's a place I know well from previous visits to this area and though I'm not
exactly local at the moment, I am staying at Aultbea, a village about 17
miles away, so it was no trouble to visit this wonderful site today.
I'd been told that it was the only black-throated type diver in the straight in non-breeding plumage, yet even so I had to scan he 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.
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.
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 too 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.
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Black-throated diver with complete chin strap, Barra 2023.
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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.