It introduces a very kudutastic concept in nature: The Egg Insurance Policy.
The Nazca Boobies in this video lay their two eggs so that one baby hatches five days before the other one. It has a good opportunity to establish itself and if it fails, then the new egg will take over. If birdlet #1 succeeds, its little brother or sister will hatch into the world and find themselves face to face with a big, bad bully who isn't prepared to share its parents. Mom and dad don't step in to help their younger child when it's being killed by their oldest, because they have successfully passed on their genes, so everything is fine.
The Blue Footed Booby essentially does the same thing, but more passively. The older chick isn't as jealous, but it's still unwilling to share its food. Often its little brother or sister starves to death.
In both of these cases, both chicks are allowed to hatch. This makes sense. It maximizes the chances that the parents will raise at least one healthy chick.
The Wattled Crane in South Africa is another bird that takes out an egg insurance policy by laying two eggs when it only plans on taking care of one little Crane. Mother Crane lays her eggs two days apart and begins incubating as soon as the first is laid, which insures that one chick will be born two days ahead of the other.
But as soon as the first chick is born, Mom quickly leads it away from the nest and abandons the second egg two days before its due date. Huh?
This doesn't make as much sense to me. Could she not wait just two more days before moving? Birdlet mortality rates can be high and what if something happens to the chick she's led away? Then she would have wasted the energy involved in laying two eggs and has no children to show for it. But at the same time, this must be a reasonably successful practice, or it wouldn't happen. Nature knows best.
Life is love.
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