Spanish Diver

[DLVelasco]

Hi,
A very odd, abnormally pigmented (some sort of melanism??) adult Black-throated Diver was photographed together with a typical juv of the species close to the same spot where the Pacific was seen last month in the North Coast of Spain.
Pics here:
http://avesmarinasdelcantabrico.blogspot.com/2010/01/colimbos.html

Note how big and bulky the bird looks in the last 2 pics, even recalling GNdiver/Common Loon.
Has anyone ever seen a diver with such colouration?

Dani

[Danacobius]

Dani, I have not seen a diver with this type of colouring before. However, the most striking aspect for me is the proportions of the head, neck & bill compared with the body. The bird looks quite absurd.

[MichaelF]

Ditto to Danacobius, very odd heavy bill and chest. What possibility it might be hybrid GNDiver × BTDiver??

Nothing to suggest that the black could be oil staining, either.

[LeeEvans]

What a remarkable beast Dani. I am assuming these images were taken very recently and if so, adult Pacific Diver and Great Northern Diver are the only species of diver generally still retaining so much breeding dress so late in the winter. Black-throated Diver generally loses most of the spangling and neck feathering by the end of October.

This really is a bizarre looking creature

Very best wishes

Lee

[John Bell]

Hi Dani et al,

I enjoyed looking at your superb pictures. Initially I tried to force a normal Black-throated into your images through a winter bird moulting into summer but this isn't the case. The upper part of the foreneck should show some pale in that case and it doesn't. In the third last picture the shape of the dark on the lower foreneck (forming a downward point) suggests a pure Black-throated. The white markings on the upperparts don't look strong enough for either species (presumably a hybrid would be intermediate or like one or the other). Hence I think your original suggestion of partial melanism is a good one. Would explain darker upperparts, dark neck and a not very obvious rear flank patch.

Hybrids are rare between divers as far as I'm aware. Natural variation is common. I welcome anyone who wishes to disagree; I usually get these things wrong!

cheers
John


Hi,
A very odd, abnormally pigmented (some sort of melanism??) adult Black-throated Diver was photographed together with a typical juv of the species close to the same spot where the Pacific was seen last month in the North Coast of Spain.
Pics here:
http://avesmarinasdelcantabrico.blogspot.com/2010/01/colimbos.html

Note how big and bulky the bird looks in the last 2 pics, even recalling GNdiver/Common Loon.
Has anyone ever seen a diver with such colouration?

Dani

[John Bell]

Further to what I just said: certainly this is a big bird. Did you see it beside any other Black-throats (or GN Divers)? Maybe the ordinary Black-throat is quite small in addition to that bird being quite big?

In Scotland I wouldn't rely too heavily on the size of the bird in separating these two. GN Diver is generally bigger and bulkier but there is a fair bit of overlap.

The full chest is a feature of both species.

Clearly you will realise all of this Dani. To answer your question I have never seen a bird like this. I have seen transitional birds but not melanism.

ATB,
John

[Alex Lees]

Hybrids are rare between divers as far as I'm aware. Natural variation is common. I welcome anyone who wishes to disagree; I usually get these things wrong!
cheers
John

That is a freaky looking beast, but to clarify hybridisation in divers isn't that rare cf: here (http://www.surfbirds.com/forum/showpost.php?p=18007&postcount=6), here (http://books.google.co.uk/books?id=MwInO7z_Y3oC&dq=handbook+of+avian+hybrids&printsec=frontcover&source=bl&ots=cAerG9vw4_&sig=pXuYz6pypWpf-ya8lWWIRgfdVVg&hl=en&ei=Y5pPS-WAAsmy4Qb6jP2UCQ&sa=X&oi=book_result&ct=result&resnum=8&ved=0CCgQ6AEwBw#v=onepage&q=gavia&f=false) and here (http://www.springerlink.com/content/mgul2pl527131245/)

cheers

Alex

[mafting]

That is a freaky looking beast, but to clarify hybridisation in divers isn't that rare cf: here (http://www.surfbirds.com/forum/showpost.php?p=18007&postcount=6), here (http://books.google.co.uk/books?id=MwInO7z_Y3oC&dq=handbook+of+avian+hybrids&printsec=frontcover&source=bl&ots=cAerG9vw4_&sig=pXuYz6pypWpf-ya8lWWIRgfdVVg&hl=en&ei=Y5pPS-WAAsmy4Qb6jP2UCQ&sa=X&oi=book_result&ct=result&resnum=8&ved=0CCgQ6AEwBw#v=onepage&q=gavia&f=false) and here (http://www.springerlink.com/content/mgul2pl527131245/)

cheers

Alex


Correction: apparent hybridisation isn't that rare. ;)

In the absence of genetics, it's largely supposition (maybe correct, maybe not). We know that aberrant birds can sometimes look like hybrids.

[Alex Lees]

Correction: apparent hybridisation isn't that rare. ;)

In the absence of genetics, it's largely supposition (maybe correct, maybe not). We know that aberrant birds can sometimes look like hybrids.

what about the mixed pairs observed with young..... have we been here before...? (!)

[John Bell]

Hi Alex et al,

Many thanks for providing these links. In the paper by C.S.Roselaar et al which concerns a hybrid White-billed X Great Northern there is a photo (Fig 1) of the bird in question. What do you think of it? I'm not wholly convinced it isn't a Great Northern (which is what it was labelled as in the museum).

I recognise a considerable amount of research has been done in preparation of this highly educational paper. The analysis does imply a hybrid. However I am unconvinced that in the cases of bill length, bill depth and in particular wing length that a larger comparison sample size might straighten the data out more favourably in favour of immer. In fact BWP / Baker (2003) gives a wing length of 400mm. The variation in the colouration of distal halve of culmen ridge is I'm sure correct with respect to the skins examined (91 in total, mainly of immer) but I would query if this might be misleading to extrapolate it to a global level? Simply speaking from experience of watching many immer in Scotland I have seen a few with very pale bills. Never pale horn yellow but definitely a very pale grey ('white-billed). These birds are also suspected of being behind several claims of adamsii. They are also possibly more likely in first year birds (as the museum specimen in question also is).

Frustratingly I have seven of the eight issues of Scottish Birds Vol 7 but, you've guessed it not issue 2 which contains details of a suspected immer X arctica written by Hunter & Dennis.

Best wishes,
John Bell



That is a freaky looking beast, but to clarify hybridisation in divers isn't that rare cf: here (http://www.surfbirds.com/forum/showpost.php?p=18007&postcount=6), here (http://books.google.co.uk/books?id=MwInO7z_Y3oC&dq=handbook+of+avian+hybrids&printsec=frontcover&source=bl&ots=cAerG9vw4_&sig=pXuYz6pypWpf-ya8lWWIRgfdVVg&hl=en&ei=Y5pPS-WAAsmy4Qb6jP2UCQ&sa=X&oi=book_result&ct=result&resnum=8&ved=0CCgQ6AEwBw#v=onepage&q=gavia&f=false) and here (http://www.springerlink.com/content/mgul2pl527131245/)

cheers

Alex

[CAU]

what about the mixed pairs observed with young..... have we been here before...? (!)

At least in passerines mixed pairs have sometimes been observed raising chicks of a pure species.