Saturday 22 February 2014

Doing subtlety at Swineham

For any non-birders reading this, you've probably heard the Common Chiffchaff, Phylloscopus collybita, singing its name on warm spring-like days like today. But you are probably blissfully unaware of the fierce debate which rages in the world of birding about the identification of the subtly different sub-species Siberian Chiffchaff, Phylloscopus collybita tristis. For the full story you'll have to read chapter 16 of the Sound Approach's Catching the Bug, or get several back issues of British Birds. But in case that's too much trouble to go to, here's a Guardian-style 'Digested Read':

Expert 1: 'Grey-brown Chiffchaffs wintering in Britain are most likely to be Siberian'
Expert 2: 'But they might be another kind of Common'
Expert 1: 'Unlikely and anyway the distinctive call is diagnostic'
Expert 2: 'Oh no it isn't'
Expert 1: 'Oh yes it is'
Expert 3: 'More knowledge of this species complex is needed. Can I have a research grant?'

So that's the heated debate dealt with: but what does this mean for the humble patch birder's chances of stumbling across a Siberian Chiffchaff? I didn't have to worry too much as Swineham's birdfinder-general Marcus Lawson did the hard work, locating three tristis recently around the gravel pits. These looked and sounded the part and responded to recordings of tristis. He also managed some photos - see here - so not to be outdone I had a go myself today. Results below, and comments welcome:
Pic 1: the first Chiffchaff I came across, this bird was frustratingly silent so the fact that calls and song might be the best way to clinch it wasn't much help! But the grey-brown upperparts and pale underparts with little hint of yellow look good for tristis.
Pic 2: taken a few seconds later from the same spot at almost exactly the same angle so a meaningful comparison in terms of colouration, this is a 'normal' Chiffchaff collybita which was associating with the bird in Pic 1. I have sharpened up both pics 1 and 2 but not changed the levels otherwise.
Pic 3: same bird as Pic 1: the eye-ring in tristis is said to be less prominent than in collybita, and lacking or merging with the longer and more obvious supercilium above the eye. The bill is also said to be smaller and blacker with an almost straight culmen giving an upturned look (Van Duivendijk). All a bit subtle to judge in the field!
Pic 4: same bird as pics 1 and 3. This shot shows very pale underparts well with hardly any hint of colour. Again, image sharpened but otherwise not altered, and taken from same spot and similar angle to pics 1-3. 
Pic 5: this very grey and white looking bird was near where Marcus had seen his, and the same place where I heard a tristis call the previous evening from a bird which didn't show very well. This one gave a better view but kept schtum!
Pic 6: same bird as pic 5 - some yellow/olive tones can be seen in the closed wing
Pic 7: Common Chiffchaff taken at the same time from the same spot and almost exactly the same angle as pics 5 and 6 so again a meaningful comparison.
Pic 8: not entirely sure about this one: in the field it looked like collybita but on the screen looks quite brown with not much in the way of olive or yellow tones. But underparts do look more sullied at least along the flanks and breast side, the super is certainly not as long or strong as birds in pics 1 and 5, and bill looks a bit stronger too. Feet and base of bill also much lighter than those of birds in pics 1 and 5. So probably collybita. Again, it uttered not a word to help with my dilemma.
Pic 9: my head hurts, so I've given up de-constructing Chiffchaffs now. I just like this picture.
That's more like it, nice and simple: white blaze on the face, big round head and clown's shoe of a bill = female Scaup. One of three on the gravel pits at Swineham.
And this even simpler: Pied Wagtail in a Wareham Churchyard. On the gravestone of the first birder who tried to sort out Chiffchaff taxonomy only to die trying.

1 comment:

  1. Hi Peter,
    You forgot to add
    Expert 1: 'Unlikely and anyway the distinctive call is diagnostic'
    Expert 2: 'But they rarely call on wintering grounds''
    Expert 1: 'That's another distinctive thing about their call'