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Hi Chris,
Easy to make suggestions on that one, not so
easy to prove. Because it hurts. / Because their mother did. / Because they are
surprised. /
However and it seems terribly obvious to me, I
suspect that the real reason is to tell people. Assuming that wild type chooks
don't do this (or most don't but I don't actually know). Surely this would
be a feature that has been selectively bred for over the centuries (either
deliberately or as suggested below) in the domestication process or maybe as a
feature linked to something else that we have selected for.
My suggested mechanism is that chickens that
advertised that they have laid an egg were seen as more valuable to the farmer
and more likely to be kept alive by the people who controlled them, for future
egg production and thus the genes that produce that behaviour increase in the
population. Whereas (regardless of how many eggs they actually lay), the
chickens that did not advertise that they have laid an egg were more likely to
be the ones not seen as valuable and were eaten quicker rather than kept for
future egg production and thus not get the opportunity to lay so many eggs.
Simple. Indeed chickens kept in a pen with others, if they made more noise
and laid less eggs, they may even be more likely to survive and pass on
their genes to the next generation than those that may have laid more eggs but
not told the farmer that they had done so. This is no different to that the pigs
that developed a more porky physique were selected for, not because it is good
for the pig, it is good for us.
As with most things in evolution, this behaviour is
not there for a purpose, it is a feature that simply finds itself in a function
and therefore gets to be incorporated in the species characteristics, after the
event.
By the way: A chicken is an egg's method for making
more eggs.
As far as I know they make the noise after
laying.
Philip
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