Here in the UK we are used to our common breeding alba, the Pied Wagtail. Basically a black and white bird, particularly the male. I've always believed that picking out the migrant White Wagtails which pass through in spring is a fairly straightforward affair. With their clean, mid-grey upperparts they usually look quite distinctive to my eye. Come autumn, with loads of young birds around, things get trickier. We still get migrant Whites, but I've always understood them to be quite doable, given good views and some caution. However, my somewhat relaxed attitude to alba wags has been blown out of the water after reading this...
My jolly mission to find myself a winter White Wagtail and thereby add a little spice to the chilly season's birding was tantamount to opening the proverbial can of worms. Confirming a [presumably] rare winter White among a horde of its common cousins is actually not for the faint-hearted.
First of all you need a 'Kodak Grey Scale'. Then you need to compare various bits of your candidate bird to said scale and see what numbers you get. This is hard. The blasted things do not let you get close enough unless they have just that moment died. They run away, and often will fly to the next field. Next you put your results through the 'Adriaens Criteria' listed in the ID paper above. Following that you either stake a claim...or creep quietly away.
The following features need assessment...
- Rump colour (in a specific area of the rump)
- Colour of mantle/scapulars
- % of blackish colour on mantle/scapulars
- Colour of flanks
- Extent of flank pattern (scores 0-2)
- Pattern of belly
- Head pattern
Then you crank a handle and out pops a result...
Well I did my best with the photos I'd taken, and I still reckon yesterday's bird is a White Wagtail according to the 'Adriaens Criteria'. However, you will not catch me claiming winter White Wagtails in such a carefree fashion again. I have learned a bit of a lesson here, and will be a lot more circumspect in the future. The reality is that the alba complex is, er, complex.
But will I go through this rigmarole again if I spot a likely candidate? You bet.
Lets face it Gav. You have an official opt out of ID clause in that paper.
ReplyDelete"However we also try to highlight the difficulties involved in this process and discuss a number of intermediate birds (I like this bit) - all of which we suggest to leave unidentified.
Excellent! if in doubt-ignore.
Yes Ric, I was surprised to learn how many are actually not safely identifiable. Thankfully, many are :-)
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