Re: Kookaburra chick aggression

Subject: Re: Kookaburra chick aggression
Date: Wed, 16 Nov 2005 11:36:31 +1100
Steve wrote "Would it be correct that the eggs hatch in the order they were 
laid?  If 
so then the first chick to hatch would be bigger than the others just 
because it is older.  What is the evolutionary explanation for this?  What 
is the guarantee that the first chick to hatch has the best genes?  Given 
an equal start, one of the others might have the best genes?  After all, 
chances are they all have different fathers."

Hatching is asynchronous and siblicide is common with the last-hatched 
chick often not surviving.  Although the brood can be reduced to a single 
nestling this is not common.  I'm not sure what genetics has to do with 
this, it's simply a matter of ensuring that the remaining chicks have a 
better start as they are not subjected to food shortages.  If food is 
plentiful the chances of the younger chicks surviving is greater as the 
older birds are satiated and less likely to be aggressive and prevent the 
younger ones from feeding.  The social hierarchy of kookaburra groups also 
probably ensures that the parentage of the chicks is the same.

A further complicating factor is that, as I understand it, there may be 
infanticide at work as well.  Males are apparently much more conscientious 
nest helpers and adults, again as I understand it, will kill the 
first-born chick if it is female.  There is apparently a real bias towards 
older chicks being male.  Therefore more males survive which has a flow-on 
benefit for the dominant breeding pair later on when that chick is helping 
raise subsequent broods.

Ain't nature grand?


David Geering
Regent Honeyeater Recovery Coordinator
Department of Environment & Conservation
P.O. Box 2111
Dubbo  NSW  2830
Ph: 02 6883 5335 or Freecall 1800 621 056
Fax: 02 6884 9382
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