Friday 3 January 2020

Be Careful HOW You Read!

Somewhere, way off to the east of us, the Chiffchaff subspecies you probably know as Scandinavian Chiffchaff (Phylloscopus collybita abietinus) peters out, and Siberian Chiffchaff (Phylloscopus collybita tristis) takes over. Needless to say, there is no neat, crisply-defined border where abietinus ends and tristis begins. There is an overlap. A contact zone.

And this contact zone (and what goes on there) seems to be the mischievous cause of much of the apparent Sibe Chiff controversy. The unrestrained sexual activity of its Chiffy inhabitants appears to have messed with some of them, both their appearance and their voice, as well as producing all sorts of DNA-related subspecific identity issues.

So, how big a problem is this? Well, the range of tristis is vast. And so is the range of abietinus. So if the contact zone was, say, the size of your local Tesco car park, well, the problem would be microscopically small, wouldn't it?

In the web book Catching the Bug (2019) by Mark Constantine, Nick Hopper and The Sound Approach, there is a fascinating chapter (entitled 'Drab') about using song and calls to identify tristis Chiffs. It acknowledges that there are problematic birds in this contact zone, but then states that according to a study by Marova et al (2009) the contact zone is less than 65km wide, compared with the total east-west range of tristis of some 4000km, and proceeds to use this 'fact' as a basis to minimise the problem. In other words, think 'Tesco car park'.

I'll be honest here. I want to minimise the problem too! So I liked what I was reading. But just to be on the safe side I thought I should check that paper by Marova et al (2009) and see exactly what it said. Well, in searching for it I came instead upon this paper...

Marova et al (2017): 'Interaction between Common and Siberian Chiffchaff in a contact zone' 
Published in Ornis Fennica 94: 66–81. 2017

In the paper is a map, from which I've cropped this bit...

The contact zone is the grey shaded area in the middle

So, is that grey shaded area really less than 65km wide? No. A quick, and very rough, muck-about with Google Maps shows it to be a good 500km at its widest. Also, it's over 2000km long. That equates to very approximately the area of England, Scotland and Wales combined. Times two!

So my hopes of a Tesco car park scenario have been dashed. And it goes to show that what you read must not be taken for granted. Verify. Verify. Verify! I could so easily have repeated that 65km figure right here in NQS, in good faith, and inadvertently misled readers.

Anyway, if you fancy having your brain sucked from your head and liquidised, I heartily recommend that paper by Marova et al. Seriously, it is fascinating.

We read on...

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