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Exploding egg decoys in rhea?
Rhea hens lay a surplus of eggs. They drop most of them in the
cock's nest (along with eggs from other hen's eggs he has fertilized!)
but oviposit extras out in the open--away from the nest.
The current best guess for why this is done is that competition favors
placing the maximum number of eggs you can in the nest.. If there are
already too many in the nest--the male limits the number--then there is
nothing for it but to lay the eggs outside the nest. When this happens
they rot and explode.
Has anyone heard of this surplus strategy in other animals, especially
An alternative hypothesis is that the eggs are decoys. Donald Bruning
(rhea expert) argues that this is unlikely simply because no predator he
knows of can get into the egg--the shell is too hard; the point being that
predator wouldn't be looking for eggs they can't crack.
Two responses are possible to that: 1. Predators might want to stake out a
nest and wait for the eggs to be pipped--predators can and do take chicks
at that point if the father has taken the majority of chicks and gone
already. Chicks almost never survive in this case! and 2. The rhea mating
system may have evolved under a different predator regime than is
currently in operation.
I suppose a fact in favor of the decoy hypothesis is that males will
abandon a viable nest if one of the eggs becomes rotten.