More white-headed intersex Wigeon weirdness

To set the context I've been interested in Wigeon with white on the head for a while, having noticed several females in different places showing patches of white behind the eye.  I blogged about this in early 2014, questioning why this apparent leucism should occur at a relatively high frequency behind the eye rather than anywhere else.  I noticed a similar phenomen with Brent Geese which fairly often show white speckling on the head but very rarely show abnormal white feathering elsewhere.

Wigeon, Buckenham, 25th January 2014

Wigeon, Caerlaverock, 29th December 2005

Then when I saw the same white-headed Wigeon at Salthouse over the course of several winters it dawned on me that my initial identification of it as being a first-winter male could not have been correct - it can't still be a first-winter male!  Its mixture of male and female features retained over at least 4 winters must surely mean it has gender issues, presumably an intersex bird.  I blogged about that at the end of last year.

Wigeon, Satlhouse, 1st December 2012

same Wigeon, Satlhouse, 23rd December 2015

Well on Saturday things took a bizarre twist.  I found another Wigeon with white behind the eye - quite a lot in fact - more than any of the previous birds.  And what was really weird is that it seemed to show a mixture of male and female features, though was predominantly female.  I think the clear-cut white-edged wing-coverts and late date for a predominantly female-like bird mean that it cannot be a first-winter male, so it would appear that it was another intersex bird.

Wigeon, Burnham Norton, 2nd April 2016

Now, in the photos the evidence of masculinity is sparser than I'd thought while I was watching it.  But I think it's there.  I don't think an ordinary female would show so much black around the tail with contrasting whitish area in front, the scapulars are perhaps a tad long and grey (?) and there seems to be a slight hint of the cream forehead showing through.  Maybe that's not entirely convincing - perhaps I should not say definitively that this bird is intersex, but it seemed that way in the field and it certainly doesn't look typical for a female.

One feature that is atypical for either gender is the dark barring on the breast and flanks.  Now it may be a coincidence (but I doubt it) but intersex Pintails seem to show dark vaguely similar dark barring on the flanks that is not present (in the same form) in normal male or female Pintail.  The Salthouse Wigeon shows a bit of this too, mainly on the breast.

So if this is an intersex bird, what are the odds of two intersex Wigeons both having white on the head if that white is simply random appearance of leucism?  Surely impossibly low?  So that would suggest that the white on the head is somehow linked to the birds' abnormal gender.  Why on earth should that be so?

If it is so, it made me wonder if ALL the Wigeons I've seen with white behind the eye might be intersex?  Most have been females, which is fine.  Intersex birds seem to be females that develop male characteristics over time, so we might expect many to still resemble females externally.  Only two were initially identified as males, the Saltouse bird that turned out to be intersex when it reappeared in subsequent winters, and one from Buckenham in 2014.  Here's the Buckenham bird... check out the breast!

Wigeon, Buckenham, 25th January 2014

This bird shows little sign of being a female - it's plumage is fully male.  But what's with those dark markings on the breast?  They aren't exactly normal for male Wigeon.  I noticed that at the time but had no explanation.  Now I can't help noticing the similarity with the dark markings on the Burnham Norton bird's breast and the Salthouse bird's breast.

So the question is, can pigment deficiency conditions like leucism be linked to gender abnormality?  And why?

And what about those Brent Geese - are they all intersex too?

Dark-bellied Brent Goose, Salthouse, 18th January 2004

Or is it just a coincidence?  Or is there another explanation I've missed?  Let me know what you think.

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?