![Image](http://vankleinwee.com/meeuwen/Forum/Argentatus_1cy_04Sep10a.jpg)
![Image](http://vankleinwee.com/meeuwen/Forum/Argentatus_1cy_04Sep10b.jpg)
![Image](http://vankleinwee.com/meeuwen/Forum/Argentatus_1cy_04Sep10c.jpg)
The only other time I've seen a similar tail pattern was earlier this year, also in Leiden, on April 10:
![Image](http://vankleinwee.com/meeuwen/Forum/Argentatus_2cy_10Apr10a.jpg)
![Image](http://vankleinwee.com/meeuwen/Forum/Argentatus_2cy_10Apr10b.jpg)
Can anything be said about this pattern (e.g. more common in northern parts of Europe)?
I haven't come across any other examples, any thoughts would be welcome.