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Re: Waiting for a giant bird and dino physiology revisted

At 08:56 AM 13/05/01 -0400, John Bois wrote:
Interesting to think of how that works for moa.  This eagle must depend
upon finding the moa in relatively open country.

Not necessarily. We have no idea how Harpagornis hunted, and given that some of the largest eagles now living are forest canopy hunters it is at least possible that Harpagornis could have been maneuverable enough to hunt smaller moas beneath the forest canopy, perhaps working from perches within the forest while making short strikes.

 And, juveniles below
some size would be immune from predation, I would think.

Why? This is quite the opposite of most predator-prey situations, and large predators will certainly take small prey if it is relatively easy (eg energy-efficient) to catch. Besides, NZ still has a falcon and a harrier that might have once been able to take chicks of smaller moas (not to mention a fossil crow that may have done the same).

I mean a monster moa sitting in the middle of the
Serengeti would be torn apart by marauders of many stripes.  Ostriches are
small enough to hide, fast enough to outpace most carnivores.

And possessed of a mean kick. Emus and dromonithids would also have faced carnivores among the Australasian megafauna, and rheas face them today.

that selection _for_ large size, and selection _against_ large size is at
equilibrium in the ostrich: further increase in size would
both slow it down and increase its visibility at the nest; a decrease in
size would also slow it down (I'm guessing).

This makes rheas a bit hard to explain! And dromornithids were a lot bigger than ostriches, and faced thylacines, marsupial lions, sebecid crocodiles, giant monitors etc.

Ronald I. Orenstein Phone: (905) 820-7886
International Wildlife Coalition Fax/Modem: (905) 569-0116
1825 Shady Creek Court
Mississauga, Ontario, Canada L5L 3W2 mailto:ornstn@home.com