Ask A Scientist Zoology Archive

name         Eric E.
status       student
age          18

Question -    This might sound a little silly,
but it's been nagging on my mind. Let me start by asking, does
fertilization have to take place every time a bird lays an egg/a clutch of eggs?
Does this mean that all eggs laid have the potential to be viable? This is
actually related to my main question about commercial chicken egg
production.  If the answer to the first question is "yes", then
how do they manage tocontinually fertilize so many hens to keep up with
high production rates?  Does this also mean that the eggs we get at the
supermarket (for humanconsumption) are actually viable? I am confused
because I think I have read somewhere that eggs for human consumptions are
actually unfertilized.
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Eric,

1.  No, fertilization does not have to take place
every time a bird lays an egg or clutch of eggs.  If
you had a pet bird, for example a cockatiel, you would
note that the female will routinely lay eggs even if
alone in a cage (i.e. without a male present).  The
eggs will be infertile, that is, they will not be able
to produce young.  This will quickly be discovered as
the eggs will begin to smell after a couple of days.
(If the egg were developing into a young bird it would
remain "fresh" smelling).

2.  No, even as in humans, all eggs do not have the
potential to be viable if they are not fertilized.
The eggs themselves are alive but will die as do all
cells if  they are not fertilized.  (The resulting
young is not immortal either).

I think the above answers should satisfy your remaining
questions.

Thanks for using NEWTON!

Ric Rupnik
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Think of it this way.  Human females ovulate each month.  If there is sperm
to fertilize them they are viable.  If not, they are expelled from the body.
Chickens are fertilized internally and then the shell forms around the
embryo.  But if fertilization does not take place the egg is laid without
being fertilized.  So some eggs that are laid are viable and some are not.  I
believe that there is a certain amount of mating that is necessary to keep
the hens laying, but I am not sure how much.  You cannot always tell from
outside whether an egg is viable except under a very bright light.  This is
called "candling".  An embryo would appear as a dark spot in the egg.  These
are removed before shipping.

vanhoeck
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