Intersex Wigeon?

I have seen a number of female Wigeons showing white behind the eye and when I found a first-winter male with white behind the eye at Salthouse in December 2012 I assumed I was seeing the same phenomenon again.  I thought it was coincidence when I saw a similar first-winter male in the same spot in February 2014 but when I heard it was back in late 2015 I realised they all had to be the same bird.  Not only were they all very similar, clearly aberrant, birds but they were in precisely the same spot, away from the main flock of Wigeon that winter at this site.  They have to be the same bird, and if they're the same bird then it can't (still) be a first-winter!

Wigeon, Salthouse (Norfolk, UK), 22nd February 2014

Wigeon, Salthouse (Norfolk, UK), 1st December 2012

Wigeon, Salthouse (Norfolk, UK), 23rd December 2015

So what is it, if not a first-winter male?  I missed a clue from the start that this wasn't a first-winter, I think.  The wing-coverts have - and have had since I first saw it - clear whitish fringes.  I believe first-winters should have browner fringes, less clear-cut than these.  It can't be an adult male with these non-white wing-coverts, so it must be an adult female.  But it has male-like grey feathers coming through on the scapulars and flanks, and the head is more solid reddish brown than I would expect on a female.  I think there's even a hint of the cream crown - just faint, but looking rather like it can on first-winter males where it's just beginning to come through.  In fact the pattern of grey male-like feathers does make it look a lot like a first-winter male - it wasn't completely stupid of me to jump to that conclusion when I first saw it!  Here's a first-winter male (already with white wing-coverts) that looks fairly similar:

first-winter male Wigeon, Horsey (Norfolk, UK), 17th December 2011

So the Salthouse bird is an adult female with some male features - an intersex, presumably.  But I had the impression that intersex birds develop over time, becoming more male-like as time goes on.  This bird is no more male-like now than it was four winters ago, so that seems surprising if it is an intersex - but what other explanation can there be?  Do some intersex birds only ever go so far towards male-like plumage?

Closer inspection reveals some other features that don't seem quite normal on male or female Wigeon.  The extent of dark barring on the breast is greater than I would expect, though this is normally variable on Wigoon.  There's also a bit of dark barring on the fore-flanks.  Maybe these are features thrown up by intersex Wigeons?  There is precedent for that happening with intersex ducks - intersex Pintail can show dark barring on the flanks, unlike any normal plumage of Pintail (eclipse male comes closest).

And the white on the head?  Is it too big a coincidence that one bird should show two different abnormal conditions (leucism as well as intersex)?  Probably not - intersex birds seem to be more prevalent among birds already suffering from some kind of abnormality, e.g. in hybrids or selectively-bred mutants.

If this is a female developing male characteristics, are we right in calling it intersex?  Or are there other conditions that lead to the same phenotypic outcome?

Wigeons with white on the head (and Brent Geese)

Just curious about this - does anyone know the answer?

Wigeon, Salthouse (Norfolk, UK), 22nd February 2014

I know leucism and other pigment-deficiency conditions can affect birds in different ways, for example making the whole bird very pale, or just making parts of the bird white, but the situation with Wigeon strikes me as being different from most other instances.

Thinking of the birds I've seen that have had patches of pure white in their plumage, this white can appear in different places on different individuals.  I've seen lots of Pink-footed Geese showing white patches but the position varies by bird (though typically it includes primaries and bands across the neck or belly).  I've seen lots of Blackbirds with white plumage, but haven't noticed any pattern as to which bits will be white.  But Wigeon seem different.  I've seen half a dozen Wigeon with obvious white patches and each one has had this white patch on the head.  The exact size and shape has varied (usually diffuse and sometimes more or less tending towards speckling) but always just behind the eye.

Here are some of them:

Wigeon, Salthouse (Norfolk, UK), 22nd February 2014

Wigeon, Salthouse (Norfolk, UK), 1st December 2012

female Wigeon, Buckenham (Norfolk, UK), 25th January 2004

male Wigeon, Buckenham (Norfolk, UK), 25th January 2004

female Wigeon, Caerlaverock (Dumfries & Galloway, UK), 29th December 2005

Why is it always the side of the head that is affected - I've never seen a Wigeon with patches of white anywhere else (I have seen generally washed out birds, but that's a different condition affecting all or most of the plumage making it paler than normal, not white).

Brent Geese are the same.  Again I've seen birds that are generally washed out, paler than normal all over, but the birds I've seen with abnormal pure white plumage affecting only a small part of the bird have all been similar - they've all had white speckling on the head, albeit varying in extent.  Here are a few, but I've far more in addition to these, all similar.

Dark-bellied Brent Goose, Cley (Norfolk, UK), 28th February 2004

Dark-bellied Brent Goose, Salthouse (Norfolk, UK), 18th January 2004

Dark-bellied Brent Goose, Cley (Norfolk, UK), 5th January 2008

Dark-bellied Brent Goose, Cley (Norfolk, UK), 5th January 2008 (second bird)

Dark-bellied Brent Goose, Salthouse (Norfolk, UK), 20th November 2004 (a bird with just a few white flecks)

Dark-bellied Brent Goose, Stiffkey (Norfolk, UK), 31st January 2009

Is this the same with the other forms of Brent Goose?  I've only seen it in Dark-bellied but that's probably just because it's the only form I see thousands of every year.



Update January 2015

Yet another Wigeon with white on the head here...

female Wigeon, Welney (Norfolk, UK), 10th January 2015

Update December 2015

Seems that the first two birds from Salthouse in February 2014 and December 2012 were in fact both the same bird, as it is back in December 2015, still looking the same.  Can't be a first-winter then and I assume it's an intersex female.  More on that in this post.

Variation in Wigeons

Every now and then I hear discussions about Eurasian Wigeon that have turned up in North America showing some green behind the eye.  Most books don't illustrate this and the sceptics cry, "Hybrid!".  Of course most of us who are lucky enough to look at lots of Wigeon this side of the Atlantic know well that Wigeon often show a little green behind the eye - it's not a sign of hybrid origin.

But what about Wigeon with complete green headbands?  Is this just normal variation?  Or are these birds hybrids?  Like these:

Eurasian Wigeon, Pentney Lakes, 31st March 2009

Eurasian Wigeon, Burnham Norton, 13th March 2010

Most people I've discussed this with consider that it's just the extreme of variation within pure Wigeons.  These birds don't show any other sign of hybridisation so they can't be first-generation hybrids, and many first-generation Eurasian x American Wigeon hybrids don't show a green headband like this anyway.  The theory is that Wigeons have inherited the mix of genes required to produce a green headband from a common ancestor but that these genes are not usually expressed in Eurasian Wigeon.  Always present, normally suppressed, but expressed in just a few individuals.  A recent discussion on ID-Frontiers seemed to reach the same conclusion but thanks to Joern, Carl Gunnar, Lars and Henry with whom I had already discussed these birds.

Whilst this theory has much merit, two observations haven't sat comfortably with it for me:

1. My experience was that Wigeon with a little green behind the eye are common and Wigeon with an extensive green band are occasional, but I'd never noticed any Wigeon with anything in between.  If it were simply variation I'd expect a continuum, with the greater extents being increasingly rare. 
2. I've heard one or two people with experience of Wigeons in Europe and in the Far East claiming that birds in the Far East have a much higher tendency to show green head bands.  American Wigeons turn up in the Far East more often than in Europe and so backcrossed hybrids might be expected more commonly there than here.  Moreover someone recently claimed that Wigeon in India (where so far as I know American Wigeon has never been recorded) never show any green behind the eye.  Thus anecdotal evidence seems to suggest that the occurrence of green on the head correlates with the frequency of vagrant American Wigeons in the population.

Well this is one mystery I made some progress with recently.  I had the opportunity to study a few hundred Wigeon at close range and in excellent light the other day.  The main thing I learned is that there is in fact much more variation than I had appreciated, and it's more common than I'd realised.  My initial observations described as point 1 above proved not to be valid - there is indeed a continuum, with many birds showing green extending further behind the eye than most, but not as far as the few.

Eurasian Wigeon, Snettisham, 8th December 2012

It still doesn't explain the geographic variation but there may be other explanations for that.  Moreover it's only anecdotal so far as I know and like my first point, maybe it won't stand up to more careful observation.  Sadly I've got no trips to the Far East or India planned so I won't be able to test that one myself - but if you travel more widely let me know if it stacks up with your experience!

I noticed a couple of other things on some of the earlier green-banded Wigeons I saw, which I wondered if they might be linked.  A couple showed a small dark (green?) wedge at the upper point of the cream forecrown, absent from most Wigeon.  However I've since found this on other Wigeon that don't have green behind the eye, so it seems not to be linked.  One also showed pale at the base of the bill extending further into the cheek area than normal, but again this seems to be a variable feature and not linked to the extent of green behind the eye.

Eurasian Wigeon, Pentney, 31st March 2009 

(the same bird as the one at the top of this post, now showing the dark wedge at the apex of the cream forecrown)

Nothing to do with the above, but worth a mention while I'm talking about variation in Wigeon, I also had the opportunity to photograph a few first-winter drake Wigeon in flight.  It's well-known that young male Wigeon lack the white forewing of adults but perhaps not quite so well-known that they continue to lack this after they've moulted their head and body feathers.  Actually it's quite well documented, so this is nothing new, but I thought it was interesting to show a couple of shots that illustrate it nicely.

first-winter male Eurasian Wigeon, Snettisham, 8th December 2012

 

Lots more photos of Wigeon on my website of course.

And while we're talking about green on duck heads where we perhaps don't expect it, here's a nice first-winter drake Pintail with a green sheen.  Not the same issue as the Wigeon here of course - in this instance I think it's just a case of how the light catches it, a bit like Tufted Duck I suppose only less obvious.

first-winter male Pintail, Snettisham, 8th December 2012

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Follow up, Feb 2013

A quick postscript following more study of Wigeon over the course of the winter.  I knew that the green on a duck's head is irridescent, i.e. the intensity of colour and the colour itself is variable according to the intensity of the sunlight and the bird's angle to the light compared to the observer.  I had even noticed that some of my observations of Wigeon with the most green on the head had been in strong sunshine (including the photos above).  But I hadn't quite realised the extent to which the light impacts the colour when the normal ground colour is chestnut-brown as on a Wigeon's head.

A few days after I posted this I studied a flock of several hundred Wigeon a bit further round the Norfolk coast in dull and cloudy conditions - not one of them showed the slightest hint of green in their head.  

Many of the questions about variability remain.  Most Wigeons don't seem to show green behind the eye even when it's sunny.  A few do even when it's not sunny.  What causes that variation is still an unanswered question, but the impact of sunlight does mean it will be difficult to assess how much it varies geographically.  As the extent of green varies according to the brightness and direction of sunlight it will be nigh-on impossible to make meaningful comparative assessments between different populations.

Thanks to everyone who has commented privately about this subject, and especially for the offers to get involved in further study in different countries, were we to find a meaningful way of doing that.