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Re: Hadrosaur nesting strategy...(was Re: The Life of Birds- Pa
On Wed, 28 Jul 1999, Larry Febo wrote:
> I don`t know for sure. The avoidance of predation upon the young I had once
> read,...somewhere (can`t remember where). Sounded like a good, logical
> reason to me. It`s amazing how much evolution revolves around raising up a
> new brood. That`s the definition of biological fitness,...the number of
> offspring that survive to reproduce on their own.
Yes. But migration, like the giraffe's neck, could have several
functions including, reduced competition, predator swamping, and the
often emphasized (but in my view secondary concern) forage availability.
As you note below, food should be available in locations that the geese
spend in non-nesting season. Indeed, as seems to be the case on
some predator-less islands, geese that find their way lose the ability to
fly and find the trade off a good one. Some geese arrive at distant
nesting sites and don't feed at all, others gorge themselves. So there is
a lot of variation in the behavior.
The "sitting duck" problem is central. Large, ground-laying birds are
extremely vulnerable to predation. This is currently being demonstrated
at the expense of duck populations in the pot hole region. Once
impenetrable, these remnant wetlands are accessible to coyotes, foxes,
racoons, etc. etc.
> Then again, not all birds migrate. How do the tropical
> variety cope (with predators)?
I believe there are practically no large ground-laying birds in the
tropics (outside grasslands and excepting cassowaries). Certainly, the
great flocks of ducks and geese are pretty unanimous in their abandonment
of predator-rich habitats in nesting season (I hope Ron Orenstein is still
in the field and I can get away with that statement).