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On Tue, 7 Mar 2000, Ronald Orenstein wrote:
> At 09:47 AM 07/03/2000 -0500, John Bois wrote:
> >I believe the rise of the grasslands explains the rise of big birds in the
> >fossil record--not that they didn't exist at other times. That
> >is, savanah grasslands are an ideal breeding ground because they provide
> >cover and productivity at low predator density.
> I think that this view may well be an artifact of modern bird distributions
> - today only cassowaries, of the larger ratites, are
> forest-dwelling. However, I am not certain that this was always so.
The rise of South America's big birds is coincident with
Genyornis' nested in the same areas as emus (suggesting a grassland
habit--for nesting at least).
> In the latter category may well be Brontornis, as well as Diatryma
> (certainly a forest bird), Aepyornis and the heavier-bodied moas like
Diatryma--now called something else--was apparently dependent on
wetlands. They became extinct when vast wetlands disappeared both in
Europe and in North America. They may have been forest birds who moved
into wetland to breed.
Of course, we placentals are not very well tuned to the imperatives of
ovipary. Nesting requirments may be quite different from the needs of
of non-breeding season.
Indeed, the bigger the bird the more predation seems to determine its
life strategies. This may be an artifact of current bird
distribution--but more likey, it's a simple fact of life: big things are
easier to find!