Northern Shoveler x Garganey

Northern Shoveler x Garganey hybrid, Mai Po (Hong Kong), 16th March 2016 - copyright John Allcock

(photo ID: 2750)

This interesting bird was consorting with Northern Shovelers and a female Garganey.  Note how the vermiculated rear flanks seem to extend to beneath the tail, which may not be expected.  A quite similar pattern is shown on the Shoveler x Garganey hybrid illustrated on plate 35 of Sébastien Reeber's new Wildfowl book (Helm, 2015).  But the long hanging black-and-white scapulars are a sure sign of Garganey influence.  A faint hint of Garganey's pale supercilium also seems to be just visible in front of the eye.

Northern Shoveler x Garganey hybrid (same bird as in photo ID 2750 above), Mai Po (Hong Kong), 16th March 2016
- copyright John Allcock

(photo IDs: 2751-2752)

Northern Shoveler Anas clypeata
Garganey Anas querquedula

Sedge Warbler x Eurasian Reed-Warbler

Sedge Warbler x Eurasian Reed-Warbler hybrid, Lac de Grand-Lieu (Loire-Atlantique, France), 6th September 2015 - copyright Sébastien Reeber

(photo ID: 2745)

Here is a rare but not unprecedented Old World Warbler hybrid.  This individual is clearly intermediate between Sedge Warbler and Reed Warbler.  The head/bill profile seems rather Reed Warbler-like to me but the pale supercilium is broader and more extensive than on Reed Warbler, while less clear than on Sedge Warbler.  The dark eye-stripe is clearer than you would expect on a Reed Warbler and in some photos you can see a narrow lateral crown stripe (upper border to the supercilium).

The upperparts colour tone is close to Reed Warbler but this bird has obviously dark centres to the wing feathers with contrasting pale edges - especially obvious on the tertials which are quite wrong for Reed Warbler.  Note too the strength of colour on the rump.  A hint of dark streaking in the scapulars is visible on one or two of the images, though these are way plainer than they should be on a fresh Sedge Warbler.  It seems to have some pale buffy coloiur extending into the collar which I would not expect to see on a Reed Warbler.  I'm not a ringer so may be misinterpreting the spread wing shot (below), but I think the way the the tip of the second primary (the outermost long primary) falls well short of the adjacent third primary is closer to Reed Warbler than Sedge Warbler (somebody please correct me if I am wrong about that).

It is sometimes said that this hybrid may be misidentified as a vagrant Black-browed Reed-Warbler.  Some hybrids may look more like that species but I don't think you would make the mistake on this individual.  The Sedge Warbler x Reed Warbler hybrid from Finland that featured in British Birds 78: 434-437 (Sharrock, 1985) has a more obvious head pattern and looks like it had plainer wings too, so some individuals may perhaps be more like Black-browed Reed-Warbler than this one.

Probably a tougher ID challenge is separating these from Sedge Warbler x Marsh Warbler hybrids.  That's a hybrid that has been proven to occur in Norway - see Journal of Ornithology 151.2: 513 (Lifjeld, Marthinsen, Myklebust, Dawson & Johnsen, 2010).

Sedge Warbler x Eurasian Reed-Warbler hybrid (same bird as in photo ID 2745 above), Lac de Grand-Lieu (Loire-Atlantique, France), 6th September 2015 - copyright Sébastien Reeber

(photo IDs: 2746-2749)

Sedge Warbler Acrocephalus schoenobaenus
Eurasian Reed-Warbler (Reed Warbler) Acrocephalus scirpaceus
Marsh Warbler Acrocephalus palustris
Black-browed Reed-Warbler Acrocephalus bistrigiceps

Black-headed Gull x Mediterranean Gull

third-summer (4th calendar-year) Black-headed Gull x Mediterranean Gull hybrid, Christopher Cadbury Reserve, Upton Warren (Worcestershire, UK), 12th March 2017 - copyright John Oates

(photo ID: 3173)

A regularly-returning bird in Worcestershire (central England) has allowed us to see how one example of this hybrid progresses from first-year plumage through to adulthood.  In the following photo when it was in its first summer (second calendar-year) the jet black head and contrasting white eye-crescents recall Mediterranean Gull but the fine bill is more like that of Black-headed Gull.  The shape of the black hood is perhaps intermediate, but certainly doesn't curve up at the rear like it does on Black-headed Gull.  The rather thin-looking reddish legs are more like Black-headed Gull.

Black-headed Gull x Mediterranean Gull hybrid, Christopher Cadbury Reserve, Upton Warren (Worcestershire, UK), 21st June 2015 - copyright John Oates

(photo ID: 2736)

John's flight shot of this first-summer bird (below) shows a wing pattern that is somewhat intermediate between the two species, though perhaps closest to Mediterranean Gull.  There is too much black on the wing-tip for Black-headed Gull, and the grey inner primaries and outer primary coverts are like Mediterranean Gull, yet the band of brown coverts across the middle of the forewing reminds me more of Black-headed Gull.

 Black-headed Gull x Mediterranean Gull hybrid (same bird as in photo ID 2736 above), Christopher Cadbury Reserve, Upton Warren (Worcestershire, UK), 21st June 2015 - copyright John Oates

(photo ID: 2737)

John tells us that the same bird had been at Marsh Lane in April 2015.  What is presumably the same bird returned to Upton Warren in 2016.  As before the blackness of the head recalls Mediterranean Gull, but the shape of the black, with white curving up at the rear, is like on Black-headed Gull.  The wing pattern is perhaps closest to Black-headed Gull with black tips to the primaries, thin black line on outer edge of outer primary and white wedge on outer primaries contrasting with greyer inner primaries.  But there is more black on the tips, which is apparent on the closed wing too, and a long black spot on the outer web of the second outermost primary.

 Black-headed Gull x Mediterranean Gull hybrid (presumed same bird as in photo IDs 2736-2737 above), Upton Warren (Worcestershire, UK), 26th March 2016 - copyright Craig Reed

(photo IDs: 2759-2761)

Black-headed Gull x Mediterranean Gull hybrid (presumed same bird as in photo IDs 2736-2737 and 2759-2761 above), Upton Warren Nature Reserve (Worcestershire, UK), 24th April 2016 - copyright John Oates

(photo IDs: 2788-2791)

It has been seen again in 2017, now in its fourth calendar-year. The wonderful photo at the top of this page was taken at the same time as this next one and both show the distinctive wing-pattern well.

Black-headed Gull x Mediterranean Gull hybrid (presumed same bird as in photo IDs 2736-2737, 2759-2761 and 2788-2791 above), Christopher Cadbury Reserve, Upton Warren (Worcestershire, UK), 12th March 2017 - copyright John Oates

(photo ID: 3174)

There were quite a few reports of this type of hybrid in the UK during the 90s when Mediterranean Gull was spreading in to the UK as a breeding bird.  More recently, as Mediterrean Gull becomes more established as a breeding bird, I get the impression that records have become scarcer again, a pattern that is typically seen when a recent coloniser becomes established.



Black-headed Gull Chroicocephalus ridibundus
Mediterranean Gull Larus melanocephalus

Mute Swan x Black Swan

Mute Swan x Black Swan hybrid, West Midlands (UK), 13th January 2012 - copyright John Oates

(photo ID: 2734)

John tells us that this first-winter bird was the only surviving offspring of a male Mute Swan & a female Black Swan that nested at Marsh Lane Nature Reserve in 2011.  It disappeared shortly after this photo was taken.



Mute Swan Cygnus olo
Black Swan Cygnus atratus

Chiloe Wigeon x Cape Teal

probable Chiloe Wigeon x Cape Teal hybrid, Trittiford Park (West Midlands, UK), 3rd March 2016 - copyright Jenny Renowden

(photo ID: 2742)

One parent of this hybrid seems easier to resolve than the other, though arguably is not the only possibility.  The reddish pink colour on the bill extends well down the bill suggesting a species with a mainly red bill, and Cape Teal fits that bill.  There are other red-billed species, and some Wigeon hybrids are known to show a pinkish bill, but the general appearance of this bird recalls Cape Teal a bit, so that seems a good starting point.  The shape of the bill, quite flattened near the tip, also fits Cape Teal, as does the black base of the bill (although the latter could come from the other parent).  Cape Teal also shows black along the edge of the bill in the distal third, like this bird, and that for me is the clincher.

But Cape Teal doesn't have so much black on the nail, it doesn't have the dark patch round the eye (the eye itself would be pale too) and it is a greyer bird overall.  A number of people have suggested a Wigeon species as the second parent, and that was my idea too.  The dark patch round the eye on an otherwise fairly plain head suggests this, as do the white tertial edges.  But which Wigeon?  Neither Eurasian nor American Wigeon have so much dark extending above the eye to the top of the head, but Chiloe Wigeon does.  The flanks are a bit orangey, which supports Chiloe Wigeon.  I wondered if such a plain bird could be produced from a Chiloe Wigeon, that being such a striking species even in female plumage, but Joern has confirmed that it can.  And what's more he tells us that there have been examples of Chiloe Wigeon x Cape Teal seen in the UK that have looked much like this.

Apparently Chiloe Wigeon x White-cheeked Pintail can also look surprisingly similar to this, so it would be helpful to get a view of the wing pattern to be 100% sure, but for now it seems very likely indeed that this is a Chiloe Wigeon x Cape Teal hybrid.



Chiloe Wigeon Anas sibilatrix
Cape Teal Anas capensis

Recent updates

proven Common Redstart x Whinchat hybrid, Lista Bird Observatory (Vest-Agder, Norway), 18th September 2013 - copyright © Jonas Langbråten

(photo ID: 2594)

Here's another of our regular posts letting you know what pages have been updated in the project recently.  As always, a big thanks to all who have contributed photos and/or insights, and if you haven't done yet or have more to offer then please get in touch.  You can comment on any thread if you have anything to say about the hybrids or topics covered, and if you have any photos you would be willing for us to use, please let us know (e.g. by emailing us).

The recent updates are summarised below but remember you can find an index list linking you to ALL the bird hybrids featured so far here:

• Index of bird hybrids

And an index list of all the bird hybrid topics covered so far here:

• Index of bird hybrid topics

So, the recent updates are:


New Bird Hybrid pages added for:

• Mallard x Eider
• White-cheeked Pintail x Chestnut Teal
• Yellow-billed (Speckled) Teal x Marbled Teal
• Herring Gull x Caspian Gull
• Herring Gull x Glaucous Gull
• Yellow-legged Gull intergrades
• Common Redstart x Whinchat

New photos added to:

• Greater White-fronted Goose x Bar-headed Goose
• Greylag Goose x Canada Goose
• Snow Goose x Cackling Goose
• Emperor Goose x Barnacle Goose
• Ruddy Shelduck x Common Shelduck
• Falcated Duck x Baikal Teal
• Mallard x Northern Shoveler
• Mallard x Red-crested Pochard
• Red-crested Pochard x Common Pochard
• Common Pochard x Ferruginous Duck
• Common Pochard x Tufted Duck
• Ring-necked Duck x Lesser Scaup
• Herring Gull x Lesser Black-backed Gull (also sound recording)
• Carrion Crow x Hooded Crow
• Intersex birds (and their confusion with hybrids)

Text updated in:

• Lesser White-fronted Goose x Ross's Goose

Don't forget you can now follow us on Twitter at @BirdHybrids

Enjoy browsing - and please do contribute where you can!

White-cheeked Pintail x Chestnut Teal

possible White-cheeked Pintail x Chestnut Teal hybrid, Victoria Park (Surrey, UK), 3rd November 2012 - copyright David Darrell-Lambert

(photo ID: 2700)

The identification of this bird is not easy and so far we have not reached a confident conclusion.  Provisionally I've labelled it as possible White-cheeked Pintail x Chestnut Teal as of all the ideas that have been presented so far this one seems to me to be the best, but we are by no means sure.

The rather long pointed tail with white sides suggests White-cheeked Pintail to me, though there are other species with relatively long tails and other species with white edges to the tail, so this is not a certainty.  The pale cheeks fit with that too, though of course there are many other hybrids that show pale cheeks, so this is not a strong supporting factor.  The brown body plumage suggests to me one of the ducks that lack bright body colours, which again fits White-cheeked Pintail (among other species), but of course we do not know that this bird is fully adult, or if it has completed its post-eclipse moult, or indeed if it is intersex.  So White-cheeked Pintail is a tentative starting point for me, not a conclusion.

If right, then the second parent must have black under the tail and a green head.  Probably a wholly green head as the green looks quite extensive, though hybrids involving Wigeon or Teal have also been suggested.  We have seen Wood Duck x White-cheeked Pintail hybrids recently and these have looked quite different, but one of my first ideas was Mallard x White-cheeked Pintail.  But this idea did not convince me, or others I asked.  Mallard hybrids usually show some hint of the curved central tail feathers, whereas this shows nothing of that.  A Chiloe Wigeon x White-cheeked Pintail hybrid looked very different with, among other things, very different pattern to the tertials and scapulars.

It was Joern who first suggested White-cheeked Pintail x Chestnut Teal, though he has been clear that he is not sure and some things seem wrong for this ID.  But the tertials and scapulars of Chestnut Teal are rather close to this bird, and the pattern of the flanks (if not the colour) could easily lead to a pattern like the one shown by this bird.  And it has a green head and black vent of course, and the bill is not dissimilar either.  But should we not expect to see chestnut colour on the body if Chestnut Teal was involved?  Certainly some of their hybrids show chestnut on the body.  Well, there's a photo of a Cape Teal x Chestnut Teal hybrid in one of the Gillham books (Hybrid Ducks: the 5th contribution towards an inventory, plate 68) and that shows only a hint of chestnut on its breast, not at all on the flanks - so rather like this bird in that respect.  We might have expected to see a redder eye on a Chestnut Teal hybrid, but at least it is not darker than that of White-cheeked Pintail (it's actually quite similar to White-cheeked Pintail's eye colour I think).

We've considered other ideas too, involving Teal, Wigeon and even Black Duck, but for me at this point White-cheeked Pintail x Chestnut Teal is the best fit.  That doesn't mean it's right though, so please get in touch if you can help clear this mystery up!

possible White-cheeked Pintail x Chestnut Teal hybrid (same bird as in photo ID 2700 above), Victoria Park (Surrey, UK), 3rd November 2012 - copyright David Darrell-Lambert

(photo IDs: 2701-2702)

White-cheeked Pintail Anas bahamensis
Chestnut Teal Anas castanea

Yellow-legged Gull intergrades

possible Yellow-legged Gull intergrade, Hyde Park (London, UK), 16th December 2006 - copyright Dave Appleton

(photo ID: 1567)

The Azorean form of Yellow-legged Gull (atlantis) is sometimes considered to be a distinct species (sometimes known as Azorean Gull), and appears to be a rare vagrant to north-west Europe with several credible claims from the UK and Ireland in recent years.  The individual shown here showed many features consistent with this taxon but some observers felt that not everything was quite right.  Specifically they felt that the tone of the upperparts was a bit too much like michahellis Yellow-legged Gull and the structure was not as it should be.  It is possible that it was an odd atlantis, and it is possible that it was a Yellow-legged Gull originating from one of the other Atlantic island populations, but perhaps an intergrade or hybrid between the two might be the most satisfactory explanation.

possible Yellow-legged Gull intergrade (same bird as in photo ID 1567 above), Hyde Park (London, UK), 16th December 2006 - copyright Dave Appleton

(photo IDs: 1567-1570)

Yellow-legged Gull Larus michahellis  
Azorean Gull Larus (michahellis) atlantis

Herring Gull x Caspian Gull

probable Herring Gull x Caspian Gull hybrid, Millennium Green, North Hykeham (Lincolnshire, UK), 22nd September 2015 - copyright Dean Nicholson

(photo ID: 2652)

Dean thought this bird was going to be a first-winter cachinnans (Caspian Gull) when he first saw it but after a longer view he started to have doubts and suspect mixed genes.  He writes:

"Size and proportions were spot on for cachinnans, head and bill shape and position of eye all good, long primaries and tertial pattern was absolutely perfect for cachinnans and the whitish head with subtle mask around eye also fitted cachinnans nicely...  I never particularly liked the well barred greater coverts but occasionally some pure Caspian can show this pattern but generally it is much more a feature of young Herrings.  I was more concerned by the retarded state of moult... it was still in full juvenile plumage which would be remarkable for a Caspian Gull on this date and should really be showing several second generation scapulars now as well as some renewed coverts.  The oak-leafed patterned scapulars were also a bit more Herring-like than I would have liked although when it flapped the underwing/axillaries looked nice and white thus Caspian-like.  When I got home I forwarded the pics to my usual gull contacts and they all agreed that this was no pure Caspian and was in all probability a Caspian x Herring which is a common hybrid pairing in western Europe now (especially East Germany and Poland) where Caspians are spreading west."

probable Herring Gull x Caspian Gull hybrid (same bird as in photo ID 2652 above), Millennium Green, North Hykeham (Lincolnshire, UK), 22nd September 2015 - copyright Dean Nicholson

(photo ID: 2653-2654)

Here is another Caspian look-alike.  Dean tells us:

"I initially called it a Caspian when I first saw it at range in heat haze but over the following days when I saw it at closer range I realised it wasn’t quite right (slightly odd tertials, dark underwing/axillaries, random scapular moult), so I circulated to my gull contacts for opinion and although there is a lot of guesswork involved with such birds, the general consensus was that it is more than likely a Caspian x Herring hybrid.  A common mixed pairing on East Germany and Poland."

probable Herring Gull x Caspian Gull hybrid, Spalford (Nottinghamshire, UK), 1st November 2016 - copyright Dean Nicholson

(photo ID: 2961-2968)

Herring Gull Larus argentatus
Caspian Gull Larus cachinnans

Yellow-billed Pintail x Marbled Teal

The bird previously posted here as a presumed Yellow-billed Pintail x Marbled Teal hybrid has now been moved back to the Yellow-billed Teal x Marbled Teal page.  Further input on this bird's ID suggest that this is the more likely identification.  Apologies for the confusion.



Yellow-billed Pintail Anas georgica
Yellow-billed Teal Anas flavirostris
Marbled Teal Marmaronetta angustirostris

Yellow-billed (Speckled) Teal x Marbled Teal

probable Yellow-billed Teal x Marbled Teal hybrid, Rollesby Broad (Norfolk, UK), 24th January 2016 - copyright Dave Appleton

(photo ID: 2612)

I suppose in some ways it's a bit embarrassing that I started off thinking this was a Yellow-billed Teal x Marbled Teal hybrid, then saw the bird in the flesh, did some research and analysis before settling on Yellow-billed Pintail x Marbled Teal hybrid instead, but now find myself persuaded that it is (probably) a Yellow-billed Teal x Marbled Teal hybrid after all.  But then again that's the point of the Bird Hybrids project - sharing thoughts, pooling knowledge and learning collectively, knowing that along the way we're bound to make the odd mistake.  And I've certainly learned a few things in the process of working this one out - for example that Marbled Teals can have yellow at the base of the bill... did you know that?  I'm hugely grateful to Joern Lehmhus for his input on this bird - his expertise with hybrid ducks is surely unrivalled!

These are the features we have considered in relation to this bird:

• The bushy 'mane', or loose mop of feathers at the back of the neck, is important.  Some have suggested that this bird is a Speckled Teal (Yellow-billed or Andean Teal, though presumably they mean Yellow-billed) - I do not believe any form of Speckled Teal can show such a bushy 'mane' as shown on this bird (possibly they may show a slight lift of the nape feathers as can many Teal species, but this is not the same as here).  For me this is the clearest indication that Marbled Teal is involved.  Wood Duck, Falcated Duck and to a lesser extent various other Teal species may show a maned effect too, but not the narrowly bushy/tufty feature shown by our bird here, which is very much like that of Marbled Teal.  Apart from Marbled Teal, I think Cape Teal and Crested Duck are the only other species (correct me if I am wrong) that come close to having a mane like this. 
• With no red on the bill (as well as for other reasons) I think we can rule out Cape Teal involvement easily.
• The dark band through the eye was more obvious in the field than it seemed in the first photos.  This is supportive of Marbled Teal involvement, though it is a features shared with Crested Duck (as well as various other species to some extent).
• The eye is fairly dark, lacking any obvious red or yellow tones.  If Crested Duck had been involved we might perhaps have expected to see something of the red eye come through on a hybrid.  I would hesitate to rule out a red (or yellow) eyed species being involved, but eye-colour is often intermediate in hybrids.
• That yellow on the bill, restricted to near the base of the lower part of the upper mandible: the pattern recalls Yellow-billed Teal and Yellow-billed Pintail, though conceivably perhaps it could appear on a hybrid between a more extensively yellow-billed species and a dark-billed species like Marbled Teal.  But a complete surprise to me was when Joern pointed out that pure Marbled Teal can show this pattern as well - here are a couple of examples: a little bit showing on this bird and more obvious on this bird.  So we cannot conclude from this that the second parent was definitely a yellow-billed species, although the two species with similar pattern of yellow would seem like a good starting point.  Note that the yellow on the hybrid is diffusely edged and less extensive than we would expect to see on a pure Yellow-billed Teal, further evidence that this is not a pure Yellow-billed Teal.
• This bird has a clear pale bluish subterminal band on the bill, a feature shared with Yellow-billed Pintail but not really with Yellow-billed Teal.  This was one of the features that most convinced me that Yellow-billed Pintail was involved rather than Yellow-billed Teal, however Joern has come up with a different, and better, explanation... it is also a feature shared by some Marbled Teals!  I did not know that, but again Joern provided some links to birds showing this (here, here and here).
• Scapular shape - I had already backed down on the comments I made last week about the shape of the scapulars being long and pointy on oxyptera Yellow-billed Teal, which were based on rushed research.  It seems that some examples of Yellow-billed Teal show elongated pointed scapulars while many do not.  Moreover some examples of Yellow-billed Pintail do too, while others do not.  The references I have access to don't seem to offer an explanation but presumably it is down to gender, age or season?  But for now, other than recognising that our bird's scapulars are not pointy (though the rear ones are a little on the long side), I'm not sure this feature helps much with the ID.
• The dark centres to the rear scapulars on the hybrid extend in a point along the feather shaft towards the tip.  That is the case on some images of Yellow-billed Pintail (examples that also have elongated pointed scapulars) but may also be the case on those Yellow-billed Teals that have similar shaped feathers (not clear in the photos I've checked).  I am not clear if this has any relevance to our bird's ID.
• The rear scapulars show broad pale tips (much broader than the pale edges to the same feathers).  My earlier use of 'globular' to describe these pale tips was an exaggeration, but nevertheless this feature is unusual and is presumably a product of the Marbled Teal involvement. No form of Speckled Teal should show such broad tips to the scapulars, so this further rules out pure Yellow-billed Teal.
• The tertials are plain lacking any pale edges.  This is fairly unusual for most species (and would again be wrong for pure Yellow-billed Teal) but is normal for Marbled Teal, so presumably inherited from that species.
• The flank feathers have dark centres with broad pale fringes.  Marbled Teal shows broad pale tips, but not pale edges to the sides of the feathers.  Yellow-billed Teal has pale plain flanks at least from the mid flanks backwards, so I did not expect to see this pattern in a Marbled x Yellow-billed Teal hybrid.  Yellow-billed Pintail on the other hand has dark-centred flank feathers with pale edges, so this seemed a more logical answer.  However, the fore-flanks of Yellow-billed Teal have a similar pattern and Joern advises that you see a similar effect on Marbled Teal x Ferruginous Duck hybrid.  So it seems that the flank pattern need not rule out Yellow-billed Teal as I had supposed.  Perhaps the flank pattern is an ancestral feature of Yellow-billed Teal, obscured in the species itself but expressed in their hybrids?  The closely related (but not yellow-billed) Andean Teal shows pale edged flank feathers.
• The above discussion of flank feathers applies equally to the uppertail-coverts.
• I suggested that the tail protruded fruther beyond the tail-coverts than it does on either Marbled Teal or Yellow-billed Teal, concluding that this added weight to Yellow-billed Pintail being the secone parent, rather than Yellow-billed Teal.  Having looked at more images of Marbled Teal I am backing down on this. Sure, the tail is longer than on Yellow-billed Teal, but I'm not so sure that it is longer than on Marbled Teal, in which case this does not necessarily require the second parent to be the Pintail rather than the Teal.
• Murray's photo of the open wing seems to show a narrow whitish bar at the base of the speculum and broader whitish tips to the secondaries.  Marbled Teal has a plain wing so I figured that this pattern must come from the yellow-billed parent, and that the pattern matched Yellow-billed Pintail much better.  On Yellow-billed Teal the inner bar is broader and browner than the narrow white outer bar.  However, the wing is in shadow in this photo and so although it was reasonable to take this as a feature supporting Yellow-billed Pintail involvement, it would need a clearer view before I could use it to argue against Yellow-billed Teal involvement if other features point that way.  It does however help rule out Crested Duck involvement, which, with a similar head tuft and dark eye-band, could have been considered as an alternative to Marbled Teal.
• In my argument for this bird having Yellow-billed Pintail involvement I did acknowledge that the contrastingly gingery tones to the edges of the upper scapulars was reminiscent of Yellow-billed Teal.  Actually all the scapulars' edges share the same colour tones but as the lower scapulars are larger the more extensive dark centres offset the overall colour, leaving the upper scapulars looking brightest.  I argued that although this was brightest on the upper scapulars, the colour extended on to the sides of the breast, which, I said, it does not on Yellow-billed Teal.  Joern rightly pointed out that the contrast is not shared by either Marbled Teal or Yellow-billed Pintail, implying that this feature does indeed support Yellow-billed Teal as a parent.  Moreover I have since noticed that on some Yellow-billed Teal images the warm tones do in fact continue on to the sides of the breast to some extent, so my argument against this does not stand up to scrutiny.
• I did already withdraw an earlier comment about the breast pattern being more barred and less spotted on the hybrid compared to Yellow-billed Teal.  That comment was made before I'd seen the bird in the flesh and it turned out not to be as clear as I had thought when making it.
• One further feature that helped convince me that Yellow-billed Pintail was the parent rather than Yellow-billed Teal was the leg colour. Marbled Teal, Yellow-billed Teal and Yellow-billed Pintail are all supposed to show grey legs.  So far as I knew the first two always do, but Yellow-billed Pintail, contrary to the text in the Helm guide to Wildfowl (Madge & Burn), sometimes show greenish legs (quite a few photos online involving both subspecies).  The legs of the hybrid are slightly dull greenish grey, so I thought that could be Yellow-billed Pintail influence.  However one of Joern's links to Marbled Teals with yellow on the bill shows a bird with clearly greenish legs, so the green colour on the legs could in fact have come from Marbled Teal.
• Finally the overall structure of the bird was something I did not comment on before.  It is a small, Teal-like bird, as would be expected if it were a hybrid between Marbled Teal and Yellow-billed Teal.  This was one of the things that made Joern think the non Marbled parent was more likely a Teal species than a Yellow-billed Pintail, and in hindsight I think that makes perfect sense.

I said before that I welcome comments and corrections as I may have overlooked something, and that proved to be the case!  Further comments are still welcome of course.

Any hybrids involving Marbled Teal appear to be quite scarce. McCarthy's Avian Hybrids of the World only cites Marbled Teal x Ferruginous Duck (though I suspect the upcoming second edition might have more...).  Apart from that I know of a Marbled Teal x Ringed Teal hybrid and maybe more will come to light in due course, but they do seem to be very thin on the ground given how commonly they are found in collections.

Note that in some of my photos the overall plumage appears greyer than in others.  The brighter more gingery toned photos are more accurate with respect to how it appeared in life.  The difference was mainly due to the ISO setting on the camera - the lower ISO setting produced more accurate colour tones but the higher ISO produced sharper photos!

 probable Yellow-billed Teal x Marbled Teal hybrid (same bird as in photo ID 2612 above), Rollesby Broad (Norfolk, UK), 24th January 2016 - copyright Dave Appleton

(photo IDs: 2613-2620)

probable Yellow-billed Teal x Marbled Teal hybrid (same bird as in photo IDs 2611 above), Rollesby Broad (Norfolk, UK), 20th January 2016 - copyright Murray Smith

(photo IDs: 2609-2610)

probable Yellow-billed Teal x Marbled Teal hybrid (same bird as in photo IDs 2609-2610 above), Rollesby Broad (Norfolk, UK), 20th January 2016 - copyright Tony Stride

(photo IDs: 2607-2608)

This bird was still present in early April:

 probable Yellow-billed Teal x Marbled Teal hybrid (same bird as in photo IDs 2607-2610 and 2612-2620 above), Rollesby Broad (Norfolk, UK), 3rd April 2016 - copyright Dave Appleton

(photo IDs: 2776-2779)

Crested Duck Lophonetta specularioides
Yellow-billed Pintail Anas georgica
Yellow-billed Teal Anas flavirostris
Andean Teal Anas andium
Cape Teal Anas capensis
Marbled Teal Marmaronetta angustirostris