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Re: Little skulls...

>>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.<<

This points toward a complex series of instinctual behaviors.  I can see why
cuckoos would instinctually switch from one host species to another when the
first began to reject foreign eggs, but why would the host species _lose_ that
trait so quickly?  Is there _any_ benefit to having your offspring killed and
then caring for a baby that isn't yours?
Perhaps there is less of brood parasitism and more brood _symbiosis_ than we