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Old Tuesday 9th January 2007, 17:26   #1
Pluvius
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Are these Gt Northern Divers

Taken this pm in Northern Ireland. I suspect they are great Northern there was seven in all plus a red throated diver. But not sure between black throated and Gt. Northern
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Old Tuesday 9th January 2007, 17:34   #2
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Think you're right with the GND, Pluvius: The shape of head and 'broken' black markings round necks are pretty good to me as is shape of head. The latter would rule out RTD, also RTDs have a tendancy to swim with bills pointing upwards. The neck markings to me rule out BTD, although head shape is simillar. Ive noticed that white flanks are less visible on GND too, when seen in water cf. the other two sp.

... have blown up pics, now having doubts!!

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Old Tuesday 9th January 2007, 18:02   #3
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The head shows at the crown and the nape to be darker than the back of 2(visible ones) of the bird, which is another feature which moves me to accept that identity.

Is that number exceptional?
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Old Tuesday 9th January 2007, 18:47   #4
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Its not that easy to tell, but I think you are right with your ID. Especially the head shape of the back bird.

Unusual to get this number together, but not exceptional.
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Old Tuesday 9th January 2007, 18:57   #5
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Sorry., look like Black-throats to me.
Too dark for GN, also the clean line between black and white on the neck and the bill isn't heavy enough.
NOT GN
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Old Tuesday 9th January 2007, 19:00   #6
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Agree, it's not straight forward as always but just to add to my comments in post1: Not sure if anyone can tell from monitors, but adult winter plumaged BTD have a very strong demarcation down the side of the neck, in the field, this looks more like a black line, cf. to lighter tones on crown,nape and back of head. (Juves are quite pale all round, and lighter than pics seem to show) The bird in the rear looks possibly to be a 1st winter GND, flanks are streaky. I note also the underwing patch on the 'rearing bird', it's extensive and more consistent with GND.
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Old Tuesday 9th January 2007, 19:04   #7
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The bird at the back has a half-collar, and none of the birds show the clear white flash on the side towards the rear, leading me to GND. But TWM, living where you do you see a lot more of these than I do, so I am hesitant.
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Old Tuesday 9th January 2007, 19:13   #8
Big Phil
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I think they are BTD also, for the same reasons as TWM and also the general lack of bulk and more rounded head shape.
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Old Tuesday 9th January 2007, 19:16   #9
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Quote:
Originally Posted by TWM
Sorry., look like Black-throats to me.
Too dark for GN, also the clean line between black and white on the neck and the bill isn't heavy enough.
NOT GN
I agree. This lot look like BTD's on my monitor. The weak bill, those flanks!, that head shape...(god I sound like Ian wallace)

Seriously...I have seen small flocks of BTD's like this but never GND's and I've just flicked thru Jonsson's beautiful 'LOMMAR' and they look like the BTD'S in that wonderful, but all too brief, swedish book.

John.
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Old Tuesday 9th January 2007, 19:28   #10
deborah4
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well said I had doubts

have enlarged and lightened pics:
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Old Tuesday 9th January 2007, 20:32   #11
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Another vote for Black-throated for the reasons others have outlined above.

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Old Tuesday 9th January 2007, 20:57   #12
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I think Great Northern. The dark/light divide on the head (especially on the back one) seems wrong for black Throated. The white patch on black throated, I thought, is normally more prominent towards the back end of the bird. The head shape on the bird at the back and in the foreground I think look good for Great Northern and the beak on these two looks quite heavy. Surely the light could be a reason for the colour of the birds?? I dunno - they just look like Great Northern!?
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Old Tuesday 9th January 2007, 21:01   #13
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Don't look heavy enough head shape to elegant and bill looks lightweight, go with BT

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Old Tuesday 9th January 2007, 21:09   #14
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I would say there is a mix. the one at the back seems to me to be a GND due to the less extensive white on the head and even line of white on the flank. I'm not sure about the two heads, and I can't work out the one with outstreched wings. however the other resting one seems more like a BTD due to the uneven line of white on the flank and more extensive patch of white on the head. the bill also seems more slender.
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Old Tuesday 9th January 2007, 21:24   #15
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Seriously...I have seen small flocks of BTD's like this but never GND's and I've just flicked thru Jonsson's beautiful 'LOMMAR' and they look like the BTD'S in that wonderful, but all too brief, swedish book.

John.[/quote]

I also have a copy of Lommar--a great little book and B-t Diver still looks good.
I think the one flapping its wings has turned its head so we are looking at its upper head!

Last edited by TWM : Tuesday 9th January 2007 at 21:27.
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Old Tuesday 9th January 2007, 21:35   #16
Larry Sweetland
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Pacific. Don't they lack the upward-curving white patch at the rear shown by Black-throated in Winter, and also lack the straight vertical black/white neck devide of Black-throated?... Nice record, but not unprecedented I gather.

Sorry, bit flippant. Seriously though can someone remind me how to separate Black-throated and Pacific Divers in Winter ?

Last edited by Larry Sweetland : Tuesday 9th January 2007 at 22:40. Reason: last post too silly
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Old Tuesday 9th January 2007, 21:41   #17
Steve Waite
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They are definatly all Black-throats. Probably the most social Diver sp.
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Old Tuesday 9th January 2007, 21:44   #18
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[quote=TWM]Seriously...I have seen small flocks of BTD's like this but never GND's and I've just flicked thru Jonsson's beautiful 'LOMMAR' and they look like the BTD'S in that wonderful, but all too brief, swedish book.



I'm apt to agree with TWM (not just because we have nearly the same initials!) - small flottillas of black-throats are quite usual whereas all of the GNs I've seen have been basically solitary (winter).
The neck markings, in my most humble opinion, aren't diagnostic (I refer to sketches made of both species over the past couple of months - each species shows some similarity, and often it's how light hits the neck etc).
www.birdforum.net/attachment.php?attachmentid=65859
www.birdforum.net/attachment.php?attachmentid=64582
The near bird is doing some contortion which I can't quite fathom, but it's possibly the top of the head we can see.
If asked to put my house on it - I'd be moving into a caravan. Personally, however, I think that we have a group of the same species - I feel sure that we'd notice a difference in scale were there GN & B-ts here.
However - I'm nearly always wrong so we must take that into account. Happy Diving.
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Old Wednesday 10th January 2007, 01:07   #19
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If its needed - another vote for Black-throated Diver
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Old Wednesday 10th January 2007, 08:35   #20
bitterntwisted
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OK, I'm happy that so many people of much greater experience agree on BTD, but I am now very confused. I presumed that the bold white flank patch and clean neck line were both necessary and sufficient conditions for ID of BTD, and that the absence of these meant GND. What about the other way round? Can a GND show a clear white rear flank patch and a clear neck line? (I hope not because that puts a line through one of my best ticks last year!)

This thread has put me back to square 1. Why, for example, is the bird in Tim's 2nd sketch a BTD. I had presumed the collar in the bottom left image to be diagnostic of GND?

If these characteristics are not crucial, what is? Head shape is variable in both species. There is (small) size overlap between species and when sea-watching size comparisons may be difficult or absent. So what is a reliable characteristic?

The point about sociability is a good and very useful one, but surely it would be rather petitio principii to use this as an ID clincher.

Summary: HELP!

Graham

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Old Wednesday 10th January 2007, 08:49   #21
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Hi Graham,

The white flank patch isn't always visible on BTD, depends on the birds posture. It can certainly be shown occasionally by RTD, but I can't recall seeing it in GND.

Cheers

Phil
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Old Wednesday 10th January 2007, 09:49   #22
Larry Sweetland
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I'd still like to know why these aren't Pacific Divers (apart from range obviously), if anyone's on it. Don't think it's too untopical given the recent report.
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Old Wednesday 10th January 2007, 09:54   #23
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Quote:
Originally Posted by bitterntwisted
OK, I'm happy that so many people of much greater experience agree on BTD, but I am now very confused. I presumed that the bold white flank patch and clean neck line were both necessary and sufficient conditions for ID of BTD, and that the absence of these meant GND. What about the other way round? Can a GND show a clear white rear flank patch and a clear neck line? (I hope not because that puts a line through one of my best ticks last year!)

This thread has put me back to square 1. Why, for example, is the bird in Tim's 2nd sketch a BTD. I had presumed the collar in the bottom left image to be diagnostic of GND?

If these characteristics are not crucial, what is? Head shape is variable in both species. There is (small) size overlap between species and when sea-watching size comparisons may be difficult or absent. So what is a reliable characteristic?

The point about sociability is a good and very useful one, but surely it would be rather petitio principii to use this as an ID clincher.

Summary: HELP!

Graham
Hiya Graham - With regard to drawing species - that's very difficult, that's why I only attempt individuals (if you get my meaning). What I mean to say is that I observe an individual of a species and make my drawings of that single bird - that way I know what I'm seeing is honest and truthful (to me and to that particular individual, on that particular day) - I would hate to then have to make a 'standard' drawing of, say, winter plumage Great Northern Diver, because the variety across individuals can be quite striking. (Incidentally Lars Jonsson makes a similar reference in 'Birds and Light' with regard to making the 'standard' id painting of house sparrow, and he goes into some detail about the problems associated with this approach.)
But back to my drawings (or, from the sublime to the ridiculous, if you wish), it certainly helps to get to grips with Great Northern Diver winter plumage (and identifying the bird correctly) when one is lucky enough to have a handful in various plumages scattered across the bay - I was able to almost follow the moult progression of the species (in general terms) by looking from one bird, in almost full nuptial plumage, through several stages of moult and finally a bird in full winter attire. The black-throats were less distinctive (I don't know, but I assume they moult quicker??!!) and showed a more 'uniform' standard of dress, (although the residual striations along the side of the neck showed well on close observation) - except the juvs, which are distinctive because of the more finely scalloped backs and head pattern (the bird in the bottom right is a juv). But once again, it was really handy (cheers God) to have a small raft of them within 50 meters.
Returning to the original photo - if there was just a single bird in the frame I, for one, would be very reluctant to state which species I thought it to be as, from that distance, and in my experience, the two can look very similar. I think they're black-throated because of their habit, not because of any colour, pattern or jizz detail evident.
Cheers - Tim
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Old Wednesday 10th January 2007, 10:07   #24
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Compare to this 2cy BtD
http://www.tarsiger.com/images/Markku/IMG_2381.jpg
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Old Wednesday 10th January 2007, 10:18   #25
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Quote:
Originally Posted by Larry Wheatland
I'd still like to know why these aren't Pacific Divers (apart from range obviously), if anyone's on it. Don't think it's too untopical given the recent report.
I don't think its possible to tell from this photo. As I recall characters of (non-breeding) Pacific are the weaker bill, lack of flank patch and presence of a chinstrap.
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