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Re: Bird mortality: North vs. South
On Sun, 6 May 2001, Ronald Orenstein wrote:
> At 05:15 PM 06/05/01 -0400, John Bois wrote:
> >Birds in the northern hemisphere generally live shorter lives than
> >southern birds. They also have larger clutches and are more willing to
> >defend their brood.
Not defend! I should have said "feed" their brood. And it's more complex
than I said: Northern birds are more wary of _offspring_ predators (e.g.,
bluejays) and reduce nest visitation rates presumably to maintain
concealment. But they are _less_ likely to reduce visitation rates than
southern birds when confronted with an adult predator (e.g., hawk).
> The potential
> for longevity may be no different; it is the survival rate in the wild that
I agree with that. But the authors have, I think, done a good job of
controling many of the interhemispherical variables. As well as
reviewing published data, they did their own study of a comparison of
three pairs of species closely matched phylogenetically and ecologically
in two study sites--one in Arizona (conifer forest) and the other in
Argentina (mixed subtropical forest). All of the relationships held
up: nth/sth fecundity and mortality differences; and the behaviors
predicted from these.