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Re: Harmonious depredations




The point that you have not admitted is that ostrich nesting is dependent
on predator presence.  Until you do so, you are saying that they have
nothing to fear from predators.  My argument depends on this
dependence.

Nonsense. Ostrich nesting is dependent on maximizing the production of young ostriches. As for predation, of course nesting behaviour can be influenced in an evolutionary sense by predator pressure (and while we're at it let's distinguish between egg predation and predation on brooding adults). That doesn't make predation the only selective factor involved.


Your argument is not that reproductive behaviour is influenced by predation. Everyone admits that. Your argument is that egg predation exterminated the dinosaurs, and as far as the ostrich is concerned you are trying to avoid the evidence that ostriches tolerate continental predation levels. As such, it is you who are arguing that ostriches have nothing to fear from predators because their current nesting behaviour is so cryptic that predators cannot locate their nests, and that therefore their survival does not affect your position that dinosaurs, which (you claim) did not or could not exhibit such behaviour, must have been exterminated by such predators.

> authoritative Handbook of the Birds of the World, with the caption "...the

Are you suggesting that this entry should trump Bertram's study in some
way?  He clearly indicates that if ostriches nest in places easily
accessible to hyenas that all nests will be taken.

Bertram's study, however valid, was not (I believe) meant to apply to every ostrich population wherever it occurs (and historically that was from the Arabian deserts to the Cape). I have already stated that predation is very high - but the point is, it does not exterminate ostriches asnd did not stop them from evolving (probably in Asia) in the first place.


> Though rheas frequently hide their nests, "the male sometimes uproots all
> the vegetation within a radius of 2-3 meters around the nest, apparently to
> isolate it, in case there is a fire".


Relevancy?

The fact that rheas will on some occasions not only not try to hide their nests in vegetation but will actually remove what might have been protecting vegetation to create a bare patch up to six meters across centering on the nest hardly suggests that they rely on crypticity to avoid nest predators!



> Emu nests are "always in a fairly
> open site, where the sitting male has a good view of the surrounding land".

"Open site" lacks definition.  Open site with grass? On sand dunes?  I'm
not being critical of HBW, only stating what we say to all our
students: you must go deeper than encyclopedias.

I am restricted by the material to hand in my home library. However, I spent two years doing field work in Australia and can certainly testify that emus are often found in areas where there is little or no tall grass. Also the HBW is far more than an "Encyclopedia", and I have not seen you provide any citations whatever on emu nest site preference.



--
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