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Booted eagle phases

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Offline lisa

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« on: October 08, 2007, 08:06 AM »
I've just bought a bargain - Fauna IbĂ©rica by Felix Rodriguez de la Fuente, second-hand on VHS  :dancing:
That's the good news. The not-so-good news is that I'm on an even bgger learning curve than I had previously thought. On Sue and Clive's recent visit Clive asked me if we had the dark (or was it the pale?) phase Booted eagles here. I was stumped by the question, having thought that the two differences in plumage were just that, phases (or morphs, as I've just found out) in the bird's development. Now then.... from what I can glean, they are two distinct colourings of the bird and in the first video there is film of two chicks in the same nest, one dark and one pale  :o
So, the dark phased Booted eagle stays dark? Why is this? Is the dark more rare than the pale phase?
 :-[:-[ and  :-[
(Before anyone says, I'm on my way to the collection on DVD! I bought the videos for Olivia's birthday - an old family tradition, always worked for my brother and me, buy someone a present that you'd like and they reciprocate. She'll learn.)

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Offline John C

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« Reply #1 on: October 08, 2007, 19:10 PM »
According to Dick Forsman (THE expert in all things concerning raptors) 80% of Booteds in Spain are pale  whilst in the Balkans & Israel its 60%.  There's also a recently described 'rufous' phase which is evidently the palest extreme of the dark morph!  Other raptors (e.g. Montagu's Harrier) also have dark morphs but within Europe I think Booted is by far the commonest example of this tendency (I believe that Spain oddly enough, also has a relatively high proportion of dark Monties).  I'm not sure if anyone has explained why these morphs occur or why the proportion should vary east & west.  I seem to recall that for some birds a darker plumage is thought to confer some advantage in cooler & wetter regimes.  I'll browse around my various books & try to come back to you,

John

Offline lisa

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« Reply #2 on: October 08, 2007, 21:52 PM »
Thankyou John. I was beginning to think everyone thought I was joking. I'm not!
www.picos-accommodation.co.uk
Accommodation, ski touring, snowshoeing, walking and info on the flora and fauna of the Picos de Europa.
SAVE SPANISH BEARS!
And now,
The Picos de Europa
Your complete English guide to these beautiful mountains of Northern Spain.