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.

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.