Description

A blog mainly about birds and birding, to supplement my website www.gobirding.eu. I shall add new posts on an ad hoc basis as and when I have something I think is worth sharing, whether that’s an interesting bird, something I’ve learned, perhaps about identification, or something that’s aroused my curiosity. Often there will be questions, some of which you might be able to answer... please use the comments!

Monday, 17 December 2012

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 observationSadly 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


_____________________________

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.

Saturday, 29 September 2012

Another non-juvenile immature skua

Following my last post about a first-summer Pomarine Skua here's another immature skua that's not a juvenile.  This one was seen on a sea watch from Sheringham in Norfolk.

I'm not completely sure if it's first-summer or second-summer.  Whilst it had a dark forehead and forecrown covering pretty much the same area as the dark on an adult pale-phase Arctic Skua it wasn't at all well-defined and didn't really recall the dark cap of an adult.  From what I've read a second-summer would be better defined than this, but do you agree that it must therefore be first-summer?  Are there any other pointers visible in the photos that enable us to age it?

And what about the species.  Having discussed it with Rob I think it's an Arctic, and that's what I thought it was in the field too.  While I was watching it I did wonder if Long-tailed could be ruled out, and I'm still not completely certain I've adequately eliminated that possibility.  What do you think?  Is there anything in the photos that clinches it beyond doubt?













probable first-summer Arctic Skua, Sheringham, 27th September 2012

Wednesday, 29 August 2012

First-summer Pom

I was hoping to come back from the Scilly birders' pelagic with photos of Wilson's Petrels to share with you but sadly that didn't quite work out (again).

Instead here's something a bit different - a Pomarine Skua in first-summer plumage.  Apparently they don't normally get many Poms down there but this year there have been a few, nearly all first-summers.  Not a plumage we get to see very often here in Norfolk, although if I'm perfectly honest it's quite possible I've overlooked it in the past.









Pomarine Skua, MV Sapphire birders' pelagic trip, 12th August 2012


Oh, and while I'm at it I might as well show off a bit of Great Shear action... something else we don't see in Norfolk very often.



Great Shearwater, MV Sapphire birders' pelagic trip, 12th August 2012

Monday, 4 June 2012

Confusing Yellow Wagtails - part 2

One enjoyable moment hunting for migrants in Sicily was finding a mixed flock of 10 flava Wagtails in a dried out pool at Capo Murro di Porco.  It contained Blue-headed Wagtails, Grey-headed Wagtails, a Black-headed Wagtail (nice call) and another curious bird, the point of this post.

Before I get on to the bird in question, let me wallow in some Grey-headed loveliness:


Grey-headed Wagtail, Capo Murro di Porco, 4th May 2012

I didn't manage to get such a good shot of the Black-headed, but it was such a gorgeous bird I can't resist sharing it:


Black-headed Wagtail, Capo Murro di Porco, 4th May 2012

And now, the bird I'm really writing about.  This was a really striking bird!  A lovely dark slaty-grey head, really dark at the front (fore-crown, lores and front of ear-coverts) but paler, almost bluey grey at the rear.  A vivid white supercilium and white lower eye-crescent, but no white in the middle of the ear-coverts.  The throat was clearly yellow but the chin was white, with white extending slightly down the moustaches.  Here it is:



flava Wagtail, Capo Murro di Porco, 4th May

So what is it?  Yellow throat should rule out the cinereocapilla/iberiae complex  I thought it might be a Romanian 'dombrowski'-type intergrade?  What do you think?

Confusing Yellow Wagtails - part 1

I was hoping to score some nice Ashy-headed Wagtails in Sicily, and so I did.  Only at one site I visited though - the wetlands at Granelli.  Only managed to get one distant shot of a 'textbook' Ashy-headed though:


Ashy-headed Wagtail, Granelli, 1st May 2012

One bird was much closer, and as it was singing its heart out and clearly holding territory it should have been Ashy-headed... but what about that supercilium?




flava Wagtail holding territory, Granelli, 3rd May 2012


Now, is it me, or does this look rather like a Spanish Wagtail iberiae?  Are there Spanish Wagtails breeding in Sicily?  I saw iberiae in Portugal a few years ago and I think most of them had a narrower supercilium in front of the eye, but variable.  Or is it an intergrade/hybrid (with Blue-headed?)?  Or can Ashy-headed Wagtail look like this?  What would you think it was if you saw it in England?


Here's another.  This one was in the same area and looked more like Blue-headed, showing both a pale supercilium and pale in the middle of the ear-coverts.  But the tone of grey on the head - that didn't look like Blue-headed.





flava Wagtail, Granelli, 28th April 2012

Both of these birds have some green on the sides of the crown.  What does that indicate?  I've seen it on Blue-headed Wagtails previously but never quite figured out if it's an age-related thing or something else.  I wouldn't have any trouble seeing the second bird above as a first-summer - when I first glimpsed it I thought it was a female.  But the strikingly colourful first bird - can that be immature?


So help me out - what are we dealing with here?



Ferruginous Ducks

A female Ferruginous Duck turned up in the Norfolk Broads a couple of years ago.  Eventually news of its presence reached the news services and lots of people went to see it.  Most of them were happy with the ID but one or two of the locals who'd originally found it and watched it for prolonged periods felt that it wasn't quite right - and was therefore a hybrid.  Last winter it returned, this time accompanied by what was certainly a hybrid, but the identity of the original bird was still doubted by some people.  I've heard three reasons cited why this bird may have been a hybrid:
  1. The head shape was wrong, looking too rounded for much of the time and lacking the peak that is associated with pure Ferruginous Ducks.  My own views confirmed that this was the case - although on occasion it could look quite peaked, most of the time it looked very round.  But was this really wrong for females?  Certainly a male looking like this would and should arouse suspicion, but I wasn't quite convinced it was wrong for a female.  However I wasn't experienced enough with females to be sure.
  2. The bill shape was considered not quite right.  Personally I thought it looked ok: although at some angles it sometimes looked a bit dubious I couldn't see anything hugely concerning in the bill shape.
  3. The white on the belly had been observed to be too indistinctly-bordered for a pure Ferruginous Duck.  I got a couple of brief views of its belly and to be honest I didn't think it was too indistinct.  Sure it wasn't as neat and tidy as it can be on a male, but it wasn't bad.
Personally I suspected it was the genuine thing, a pure Ferruginous Duck.  But although I've seen a few Ferruginous Ducks they've all be in the UK where any record is tainted with the possibility that it's escaped from a collection and may not be pure.  Also most of the birds I've seen have been males.  I simply wasn't experienced enough with wild female Ferruginous Ducks to be able to make a watertight case for it being a pure bird.  It certainly wasn't a first-generation hybrid but a hybrid backcrossed with Ferruginous Duck would be feasible in captivity and some people felt this was the most likely ID.


Ferruginous Duck, Cockshoot Broad, 12th November 2011

In Sicily I got the opportunity to study a number of Ferruginous Ducks in the wild that were free from the curse of uncertain provenance and were unlikely to be hybrids (at least not all of them!).  I learnt the following:

  1. The rounded head shape shown by the Norfolk Broads bird was perfectly normal for female Ferruginous Duck.  Just like the Norfolk bird, the females I observed in Sicily changed their head shape according to posture, sometimes looking peaked but most of the time looking rounded.  I could see no difference in head shape between the Norfolk bird and the birds in Sicily. 
  2. The apparent bill shape varied too.  Some birds, some of the time, seemed to have much less impressive bill shapes than the Norfolk bird.  Of course this has more to do with angle to the observer than anything else, but there did seem to be a little variation in the bill shape - some females seemed to have fractionally shorter and more concave bills than expected.
  3. Females seen in flight and rearing up clearly showed variation in the belly pattern.  Some were less well-defined than the Norfolk bird.  One bird was much less so, although I did wonder if the poor definition on that bird wasn't caused by dirt rather than actual plumage pattern.


 Ferruginous Duck, Granelli (Sicily), 1st May 2012










Ferruginous Ducks, Granelli (Sicily), 29th April 2012

I noticed a couple of things about the males too that I've sometimes wondered about when I've observed this on birds in Britain:
  1. The head can look rounded on males too, though with prolonged viewing it always reverted to the classic peaked shape.
  2. The contrast between the breast and the flanks varies according to angle to the light.  The same bird can change from having no discernible contrast whatsoever between the colour of the breast and the colour of the flanks to having such a strong contrast that it made me think for a moment that I must have found a hybrid. I knew this was the case on some of the British birds I've observed but it was reassuring to see that it was also the case on genuine wild birds in Sicily.



Ferruginous Ducks, Granelli (Sicily), 29th April 2012

Lots more photos of Ferruginous Ducks from Norfolk and from Sicily at http://www.gobirding.eu/Photos/FerruginousDuck.php