November 25th   Leave a comment

Great northern, black-throated and red-throated divers (top to bottom): (John Anderson). Head shape and eye position is a really good way to split them. Bill shape is also good but seems to be more useful only with closer views.

To finish off divers…John got another series of great black-throated diver pictures on the water today which made me think again about what makes them very different. If you look at their heads, red-throated divers have their eye very far forward, almost touching their bill (making them look beady eyed even in flight) and a gradually sloping forehead. Black-throated divers have a forehead extension that makes their eye look closer to the middle of the head, but still obviously closer to the bill than the back of the head. Their forehead is steeply sloping. Great northern divers are more so – eye now looking like it is in the middle of the head because of a bulbous forehead extension that is now very steeply sloping, giving a square front to the head. There are lots of other differences of course, but in bouncy sea at a distance, the head shape and relative eye position is usually visible. If you want to get some diver practice in, try Outhead (the end of West Sands, St Andrews), at the Eden mouth and just out to sea. A mid tide seems pretty good to get the divers coming relatively close, as they fish in the river channel.

Posted November 25, 2021 by wildcrail in Sightings

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