birding-aus

Fw: Faulconbridge Gang-gang Cockatoos

To: Jill Dark <>
Subject: Fw: Faulconbridge Gang-gang Cockatoos
From: Andrew Taylor <>
Date: Mon, 20 Jul 2009 20:27:57 +1000
There seems to be little evidence of biased sex ratios in birds so the
observer is likely mistaken when they say their local Gang-gangs usually
have 1 female & 1 male offspring.  Two is apparently the normal Gang-gang
clutch size but only 50% of these clutches should be male-female (and
25% male-male and 25% female-female) unless something quite remarkable
is happening.

Sex-dependant survival rates are known, e.g:
http://galliform.psy.mq.edu.au/Megapode_project/Reprints/goeth&booth.pdf
but given the number of birds involved chance seems by far the most
plausible explanation.

Andrew

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