Re: White Rock Eagles

RE White Rock: From the beginning I see the female eagle as different than last year.  She arrived on a different day, and has not laid on the same date.  She looks a totally different bird to me!!  Because eagles are driven by the light cycle and not by temp or weather, they are creatures of habit -- the light cycle drives that habit or periodicity.  Many migratory birds that have to arrive at the "variable moment" that the arctic opens up and reveals their "pond" have to be fine tuned by the local weather.  Not so with eagles.  We see them laying eggs, incubating etc. under a late snow fall.  The light drives their cycle and a little storm is not getting in the road of day-length! 

Since the female did not return on time the male was deciding about what female to accept.  He passed on three options and accepted -- in my theory -- the forth female option.  She has a different latent timing.  Note, in the previous 2 years the female laid her first egg on March 13.  Why would she not lay again near that date?  Has she a cancerous ovary?  The sun cycle is the same -- give or take our artificial leap-year day option.  Since they mate for months in advance the cycle is not really interfered with by total synchronization of all parts of the breeding cycle.  By this I mean the male and female can have reasonably different biological cycles, but since they copulate since October this would not affect the viability of the eggs.  Over a period of weeks they can exhibit nest building, etc., a small element compared to the allowance of a female to let the killing talons of a male sit on her back -- an ultimate bonding act.  She can be mated and carry sperm for months.  When her cycle produces the sequence of eggs out they come -- fertile -- but different cycles for each pair.  However she responds to the sun cycle the same way each year.  Since they copulate for months (Oct. to July) this does not effect fertility.  So in the case of the White Rock pair the "new female", if I am guessing correctly, is slightly different in timing to the previous female.  The male has been happy to mate for months so the eggs should be fertile -- whenever they come.

Christian and Tina think the female is the same (( I just now heard from Christian that he is now thinking the female is different and is going to review images in detail)) -- apparently because she uses the same perches.  This was the  same reasoning that Doug Carrick used to confirm that his late arriving Hornby female was the same.  I can assure anyone that each territory has very obvious perches that would appeal to any territory owner -- these few perches permit an overview of the hunting / breeding area better than others.  In flying I could readily pick out the good perches and, as the season progressed and the adults arrived back, they would use these expected perches -- and I could readily see why.  These perches gave the commanding view of the area.  This is apparent to me flying over as it is to an eagle seeking a commanding position to find food or see its nest etc..  Each territory has few such commanding perches -- many areas have very few options.  Therefore seeing a bird pick one of these commanding perches only makes sense - I would do the same.  Any bird would make the same choice is my point.  Therefore using the predictability of a perch to determine a specific bird I think is not terribly meaningful. They have few "choice" options.  Therefore I put more credence on behavior, certainly on markings that are sometimes unique, but most importantly on behaviour timing -- which is driven by the light cycle.   I so wish we had banded White Rock eagles and others.


David Hancock

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