Friday 3 May 2019

Flava Flav - "Harder than you Think"

With birding, there are certain cans of worms that are generally left unopened until one is forced to. One such can is the whole Yellow Wagtail complex with the various subspecies which all look bewilderingly similar. I have to 'fess up right now that in a fit of enthusiasm quite a few years ago I bought the Helm "Pipits and Wagtails" book but since then I've not really used it at all, chiefly because I've not really had any cause to. This all changed in the last couple of weeks when a couple of interesting subspecies turned up in Oxfordshire which finally forced me to at least start to get to grips with it all. So largely for my own education, but also in case it's of interest to readers, below I've laid out a summary of the complex. Please note, I've missed out a few of the minor subspecies in this in order to make it simpler:

Main Points for Adult Male Yellow Wagtail Complex

British Yellow Wagail (M.f. flavissima)
Here in the UK
Yellow head, supercilium,  yellow throat

------- the blue headed variations -----

Blue-headed Wagtail (M. f. flava)
West Europe and west Russia
Blue/grey head, supercilium, yellow throat

Syke's Yellow Wagtail (M. f. beema)
Kazakhstan, & SW Siberia
Blue/grey head, supercilium, yellow throat, white lower cheek area

Eastern Yellow Wagtail (M. tshutschensis) - now a full species
Central and south eastern Siberia
Blue/grey head, supercilium, yellow throat, ID'd on call or DNA

Spanish Wagtail (M.f. iberiae)
Iberia and NW Africa
Blue/grey head, supercilium, white throat

------- the grey/black headed variations -----

Black-headed Wagtail (M. f. feldegg)
South east Europe and Asia
Black head, no supercilium, yellow throat

Grey-headed Wagtail (M. f. thunbergi)
North Europe and North Siberia
Grey head, no supercilium, yellow throat

Ashy-headed Wagtail (M.f. cinereocapilla)
Italy, Sicily & Sardinia
Grey head, no supercilium (or just a hint), white throat

In terms of how they're identified it's all down to subtle things to do with the combination of the supercilium, the head colour and the throat colour. I've picked out the key points in the table in order to make sense of it all. Of course the females are all much harder to ID - don't even go there!

So the first of the two interesting birds was one found by RW late one afternoon at Farmoor. Looking almost monochrome in terms of colouring, this first winter bird immediately had us all hoping for Eastern YW which as a separate species would be a tickable Mega for Oxon. Apparently it's possible for more western bids to look like this as well in certain circumstances so to claim EYW requires either DNA evidence (so poo or a feather) or at least a recording of the call

First winter Yellow Wagtail species, perhaps M. f. beema (Syke's Yellow Wagtail), courtesy of Roger Wyatt
Our esteemed county recorder IL pointed out that this bird has pale cheek coverts below the eye which isn't a normal characteristic of EYW and is a feature which is diagnostically generally only shown by M .f. beema (Syke's YW). Sadly, the bird was only seen one other time by one other observer a few days later and despite a last gasp twitch to try and see it myself on the second occasion, it was nowhere to be seen. Thus it has to remain unidentified to sub-species (or even species) level though it did prompt much debate amongst Oxon's birding community.

Fast forward to the first day of May and post afternoon tea, I decided that I needed to get out of the house to stretch my legs so decided to wander down to the Meadow. There I met TM, who, as a young student birder has become more obsessed about birding Port Meadow than even I was when I first started (and that is saying something!). Sadly the years of patch birding has taken their toll on me and I'm not as keen as I used to be but TM has taken up the baton with gusto and visits far more often than I do. As I strolled up to Burgess Field gate I spotted him hunched over his scope, though as there were no flood waters left any more (they were dried up in the recent spell of hot weather) I couldn't help but wonder what he might be looking at. As soon as I arrived he excitedly told me that he had a dark headed male Yellow Wagtail species. He shared a few photos that he's phone-scoped and it did indeed look like a bona fide male continental Yellow Wagtail species of some sort. I took a quick look through his scope, put the word out and hurried home to get my scope (which I'd not bothered to encumber myself with now that the floods were gone).

Photo courtesy of Thomas Miller

Upon my return I set about examining the bird for myself and comparing it to the photograph that I'd taken on my phone of the appropriate page in the Helm guide. The first thing to note was that it had a grey head of some type but no supercilium at all. That immediately ruled out whole bunch of candidates and left: Grey-headed, Black-headed and Ashy-headed. As other county birders started to arrive we debated the ID back and forth for some time. The bird definitely had a grey rather than black head with a noticeable mask effect, reminiscent of a Lesser Whitethroat. The lack of a black head ruled out  Black-headed and so left either Grey or Ashy-headed with the main differentiator between them according to Helm being that Ashy had a strong white throat whereas Grey had a yellow throat. Now, this is where it started to get tricky. As you can see from the photo above, it does at first glance seem to have a white throat but when actually looking at the bird through the scope, it was more of a very pale lemon wash rather than a clean white throat. Thinking about it later, it was certainly possible that in the rather overcast conditions and against the dark head the paler throat was burning out somewhat in the photos, making it look paler than it was. Take a look at the video below where it looks less white than in the above photo, though still definitely paler.

Video courtesy of Badger

Also in this photo below (taken as a grab from the above video) you can see that it's less white looking....

Grab courtesy of Jason Coppock
In the end we realised that we were at the limit of our experience on this and needed to wait for someone who actually knew what to look for to come and tell us what the ID was. Gradually the other birders drifted away but I decided to stay on just so I could keep tabs on the bird until more people came - I knew that IL at least was on his way as he'd called earlier. Eventually the next shift arrived and I headed back to cook a rather late dinner for my son and myself. As I was departing IL arrived and he said that from the photos he'd thought it was a Grey-headed and once he'd had a chance to look at the bird in the field he was soon able to confirm this for definite.

The first wave of twitchers all puzzling over the ID

Interestingly enough, an Ashy-headed Wagtail was actually presently on the Scilly Isles. From looking at photos you can see that there's no doubt about the demarcation between the white throat and the yellow breast  - something that was clearly lacking with the Port Meadow bird and which made the Meadow bird the Grey-headed that it turned out to be. So for me one of the take-aways from this is that for the white-throated species in the complex, it's not just that you think the throat might be white - there really shouldn't be any doubt about it.

Ashy-headed Wagtail on Scilly presently, taken from the Scilly Spider blog, all rights reserved
In terms of past records in the county, this is only the third one. The only other two were way back in 1992 where two were found in the same year, one at Farmoor and one on the Downs during a mini national invasion that year. So in terms of rarity this is a definite county Mega!

All in all as they say an educational bird. I'm personally glad to have opened this can of worms and feel that I have a much better grasp of the whole Flava complex now. Now, if only I dared to get to grips with the female side of the complex! Flava's - they're "Harder than you think"

1 comment:

Jeremy Dexter said...

Great write up Adam. There is a very good article on the 'Lothian' Grey Headed Wagtail from Martin Garner on the 22/5/03. Should be available on BirdGuides. Seems to fit our bird.