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Cain and Abel syndrome

> Cain and Abel syndrome, or simply cainism, is the killing of a nesting

> bird by a nestmate, always the first and oldest bird.

True, and because of this certainty, there is no real relationship
between the killing of one of the chicks and survival of the fittest.
Rather, it is "survival of the first born", which may or may not
be the fittest of the brood.

 > It is most
> dramatic in eagles, especially Aquila.  It is the result of the eldest

> sibling either starving the younger sibling to death or actually
> directly killing the younger sibling.  It almost always happens in
> clutches of two to three birds.  In the Verreaux eagle there are
> only one bird that surivives out of a clutch of two.  It is very
> in the bigger birds and less common in medium-sized birds such as
> to rare in smaller birds.

Size probably relates to relative biomass consumption, as well as the
predator/prey ratio (see below).

> It is thought that cainism is related to the abundance of food.

More specifically, it is probably related to maintaining a proper
ballance in the predator/prey ratio. (usually 3%-8% of all taxa
in any particular ecosystem are carnivores).
Omnivorous birds (the majority of all extant avians) show little
inclination to this culling effect.

In the Hell Creek paleo-ecosystem, to take one example,
predators are 7% of the total paleo-population density.
(The predator percentage jumps to 12% of the total population
density if ornithomimids are counted (an "iffy" proposition at best,
that they could be herbivores for all we know, or at least omnivores).


White, P.D., D.E. Fastovsky, and P.M. Sheehan. 1998. Taphonomy and
suggested structure
    of the dinosaurian assemblage of the Hell Creek Formation
(Maastrichtian), eastern Montana
    and western North Dakota. Palaios, volume 13:41-51.

                Phil Bigelow