Monday, May 21, 2012

Almost Cain and Abel

Some quick sketches from watching this enchanting webcam: Cornell Herons

Harassed parent scratching chin
Is this a crack I see before me?

Eggs about to hatch

Great Blue Herons (Ardea herodias) nest in rookeries, and lay 2-6 eggs. Parents share incubation duties, with males taking the day shift, and females the night shift.

Unlike many other birds, herons and egrets (and birds of prey) start incubating the moment the first egg has been laidresulting in a large firstborn, and a succession of increasingly puny chicks, as each hatchling has to compete with its older, heftier siblings. Some heron chicks are more equal than others.

Goneril and Regan

While great egret (Casmerodius albus) chicks actively stab their siblings to death, great blue herons may simply starve their younger siblings by outcompeting them when food is scarce. This raises the question of why herons and egrets evolved to have more offspring than they can reliably support. One idea is that by creating an age and size disparity in offspring, parents can allow for environmental unpredictability at minimal cost. If times are good, then all the chicks survive, and if times are hard, the runts perish, but being the youngest, they've had the least invested in them anyway.


Spotted hyenas also appear to be siblicidal, which could explain why females have evolved bizzare mimetic penises that make childbirth a nightmare -- but that's another story.

For an excellent account of familial conflict, I highly recommend "More than Kin and Less Than Kind" by Douglas Mock.
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