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Re: Little skulls...



At 07:34 AM 10/20/99 -0700, Bill Adlam wrote:
>The only nest parasite I'm remotely familiar with is the European
>cuckoo.  In this species the eggs are disproportionately small, to
>mimic host eggs.  However, the hatchlings grow larger than the host
>chicks, are often larger than the host adults by the time they leave
>the nest.
>
>I've heard of some research indicating host birds are good at
>distinguishing foreign-looking eggs, but very bad at recognising alien
>chicks.

It is a touch more complex than that.  Here in North America, the main
nest-parasite cuckoo varies its hosts over its range.  Also, in any given
area it often has two or three hosts.  There seems to be a dynamic
interaction between host rejection and host choice.  In areas where cuckoos
are more common, hosts tend to be more able to reject cuckoo offspring.
Where this happens, the cuckoo apparently tends to switch primary hosts to
one that is less discriminating. Once this happens, the original host
apparently starts to *lose* its discriminating ability, so eventually the
cuckoo switches *back* to that host.

[Note, much of this is reconstruction based on subtle patterns of
host-cuckoo interaction].

--------------
May the peace of God be with you.         sarima@ix.netcom.com