Delta OWL Bad Eagle Egg Analysis


The sad end to the two egg clutch of the Delta OWL bald eagle pair has almost come to an end.  You will recall that this pair tried nesting for 3 seasons at this site without success.  The first year the eggs did not hatch after a marathon incubation of nearly 60 days.  Then in the 2010 spring the nest started to fall apart under them.

It was startling to see the two adults standing on the nest and the center of it fall out below -- them leaning forward watching the center section falling to the ground.  This was apparently too much and they made no little further nest building effort and did not lay any eggs.  This was followed by the entire nest remnants falling from the tree.  When we went up for the fall cam cleaning etc. we decided to place some new solid nest supports in the tree and place a considerable pile of sticks as an incentive.  It worked.

This past fall on their return to the territory little happened.  The pair seemed to again do little about nest building.  Then when many of the viewers had given up hopes -- two eggs were laid.  Then the waiting game.  Then again the disappointment.  The 35 day incubation period passed and not even a pip.  At just over 50 days one egg disappeared. The remaining egg was abandoned but remained in the nest.

This seemed an opportunity to test the egg for fertility and possibly for heavy metals and pesticides etc.  I did not want to be seen in the nest but this pair was consistently failing and possibly getting some explanation seemed worth the risk of the pair abandoning the site in future years.  And besides, their abandonment of the site might allow a more productive pair to settle in there.

In any case, during a discussion with the Ministry of Environment, collecting the egg for analysis seemed like the best option.  Quickly I got tree arborist, Jason Stoppa, to volunteer his evening and he whisked up the tree and brought down the remaining egg.  I then took it out to the British Columbia Animal Health Centre for analysis. 

The BC Ministry of Agriculture pathologist, Dr. Vicky Bowes, first gave us her preliminary analysis.  The egg had a lot a fine hairline cracks that could have allowed entry of various bacteria.  Her conclusion on fertility was that the egg was likely infertile.  However, with the massive bacterial contamination and decomposition, it would be very difficult to be certain of fertility should it have been terminated in the first few days.

The conclusion is that without discernable embryonic development we can assume the egg was likely not fertile.

So what next?  Well not much.  It turns out that to put one contaminated egg through very extensive and expensive analysis for pesticides and other contaminants is not practical.  This is not a TV series.  This is the real world.  Getting this detailed review outside some broader based study of many eggs does not allow the proper context to understand such singular results. The egg sample has been frozen and will be kept on file for inclusion in the next extensive study of eagle egg tissue.  The conclusion:  one egg analysis does not an effective or justifiable scientific study make!

The final conclusion.  Our Delta OWL bald eagle pair has failed to produce young for three years.  Maybe they can't.  If the problems are simply about this pair learning to effectively mate then perhaps practice will make perfect.  Let's hope year four is more productive at this site.

Thank you all for your interest.

David Hancock.

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