Thoughts on the failure of Delta O.W.L. eagles - again!


Hancock here:   some thoughts on the failure of Delta O.W.L. eagles - again!

The Delta OWL eagle pair are well on their way to setting an undesirable record.  This is their 3rd year of failure.  However, I have another non-cam pair that has outdone the Delta OWL by a long way.  This 2011 is their 12th successive year of failure.

What are the reasons.  The short answer is we don't really know.  Are both or one of the parents infertile?  Have they just not learned the reproductive techniques and produce infertile eggs?  Did the incubation period get disturbed so that the eggs got cold and failed?  Perhaps the eggs were fertile but with low viability due to some inadequacies within the parents?  Do they frequent the two local landfills and have they absorbed a lot of contaminants?

Some options.  It is tempting to collect the remaining egg to have it tested for pesticides, heavy metals etc.  ((Note I broke off here and contacted the MOE (Ministry of Environment) and received encouragement to collect the egg for analysis which we did this evening.)) From egg collection and analysis we might gain some insight into the parents' biology and health.  To be honest I thought the egg would be taken quickly by ravens, crows or coons. 

Lets review some of the issues in broad sweeps. 

Were the eggs fertile?  We don't know but fertile eggs that fail usually rot from the inside and explode within a couple of weeks of failure.   If the eggs had pipped and died at hatching, the likelihood is that the deteriorating egg, exposed to outside bacteria, would more quickly deteriorate.  A pipped egg is of course already a weakened shell and more easily broken or crushed.

My best guess is that both the eggs were infertile to last as long as they did.

Other options --- related to health of adults: without egg analysis we are guessing.  However, with people watching these birds pretty regularly, day and night, these is no apparent large disturbance to the incubating birds reported.  Furthermore, most people seemed to think both parents were relatively good sitters -- incubators. This further suggests to me the eggs did not hatch because they were infertile.

Was one egg pipped?   Possibly but my review of the 'so-called pipped egg' does not conclude the egg was pipped.  This remaining egg supposedly was pipped.  The examination today confirmed my belief that the egg was not pipped.   The fact the egg retained its full integrity for so many days seemed to say it was not pipped with a weakened structure.

The nest structure:  Certainly this pair, which we suspect were the original builders of the nest, built what appeared to be a good "first nest".  Well of course it did fall apart in the second year and this suggests some failure on their ability in placing the structural details. The second year, when the center of the nest fell out, the pair did not make any attempt to rebuild the nest.  Many adults losing a nest in March or even April, will start another nest.  They had lots of time to rebuild the nest. They chose not to do so.  Then the entire nest fell from the tree during the summer months.  And this season, arriving back to find the new base platform, this did not stimulate them to do a lot of supplemental building.  They only did moderate modification before laying their eggs.  Not much preparatory effort.  Perhaps not good parents.

Now that we have the egg for analysis let's hope it yields some interesting clues.

A big thank you to Jason Stoppa of Urban Grove Tree Care and Consulting who donated his tree climbing services!!

David Hancock

Thank to Darlene for posting the egg retrieval video on YouTube here:


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