Wednesday 20 January 2016

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

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