Friday, December 11, 2009

Blackcaps - one or two?

In recent times a migratory divide has been noted among southwest- and northwest- migrating Blackcaps - with birds wintering in either Spain or the UK. Both groups of birds face particular challenges, the Spain migrators dependent upon fruit on their migration route, while the pressures of the UK population appear to have been alleviated by our winter feeding techniques - we have enabled their survival. Over a very short time-span, in evolutionary terms, this situation has resulted in two 'ecotypes' where the birds, returning to shared breeding woodlands, are no longer breeding with each other. This could be the start of different subspecies and, indeed, it is already apparent. The 'new' northwest migration route is shorter and, as a consequence, birds on this route have developed shorter, rounder wings, giving greater maneuverability but being less suited to longer migration. They also have longer, thinner bills - less suited to eating fruits (which they no longer need to do).
There is a bit more science on whether "geographical seperation is necessary to drive speciation" - which this work appears to refute - but if changes have occured so rapidly in one direction they could equally be changed to another just as quickly.
Full article published in Current Biology on-line 3rd Dec; but also see:


Anonymous Chris Tynan said...

Hi Bob,
Flew to the Algrave in Portugal the other day. There was lots of Blackcaps, Song Thrush and Chiffchaff's there too. The pomegranite looks a favoured food source plus other beeries.


4:20 PM  

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