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What can Stop an Eagle Laying?

Interesting question.  The process of laying an egg is not without some considerable preparation on the part of the female.  Probably some months — maybe a few weeks in eagles — the body begins to prepare for the egg.  The pair bonding, the hollering, the courtship flights, the intimate moments including frequent mating,  has already stimulated the flow of hormones and started the process by which the ovary starts to develop minute eggs into full sized yolks that will erupt the body.

So for a few months the development is within the ovary but there are simultaneous changes taking place in the oviduct. It is growing the different areas where the protein and shell layers will be secreted from. Then when the moment is right the ova bursts out of the ovary into the body cavity and is hopefully caught up by the enveloping infundibulum and transported downward into the oviduct.

Now in this total process where is the “disruption” of the cycle about to take place?  Is something going to interfere with the female’s development to stop the ova development before it is shed into the body cavity?  If so then the various ova that are in the ovary will simply be re-absorbed and the ova reduced in size.  That will probably result in no further breeding opportunity that season for that eagle.  Some very prolific smaller birds, even after being sufficiently shocked to cause the above absorption, might have time to re-start the whole process.  Not likely in eagles!

If on the other hand if a sufficiently  harsh disruption occurs during the transport of the fertilized yolk down the oviduct, I believe there can be re-absorption but more likely there will be an abortion — the delivery of an imperfect egg.  I have seen distressed birds, not an eagle, produce eggs without shells, without the white albumen etc.  Sometimes we get distressed birds that produce only tiny eggs, miss-colored eggs or even misshapen eggs.

If the disruption happens when the egg is nearly at term or the disruption is not necessarily terribly great, yet the bird is not able to lay the egg in the nest, then the bird may simply lay the egg somewhere else.  We have two pairs of geese that lay here each year but the dominant pair doesn’t tolerate the second pair very much. The result, since the second pair always want to hot-nest, that is drop their eggs in the same nest as the first pair used but only the day after the first pair leave, the second pair have to wait for that first goose to leave with the goslings.  Some years we find a “first egg and sometimes the second” lying around the pond or in the fields. The second goose could not hold the eggs so dropped them nearby.  As soon as the first hen left the second finished her clutch in the nest.

It is possible an eagle could “not have the nest ready” or it “not be  satisfactory” and she could drop the egg elsewhere.   The same might happen if a nest was disturbed and considered unsafe by the female between laying the first egg and being ready to drop the second egg three days later.

Lots of options — re-absorption before ovulation, absorption during passage down the oviduct or dumping of the egg.  It often seems that success is so much less likely than failure.  Let’s face it. Birds have been practicing this routine for millions of years, even the bald eagle has been around over 100,000 years and the end result is that they have evolved a working system.  Wouldn’t it be nice to think we humans could be that well adapted.  I doubt our few thousands of generations have had time to so effectively evolve solutions.  We can’t even evolve how not to soil our own nest!  Sorry about that — it’s hard not to get upset when talking about humans. Eagle are so much more relaxing.

David Hancock