Re: Hadrosaur nesting strategy...(was Re: The Life of Birds- Pa

[John Bois <jbois@umd5.umd.edu>]

On Fri, 30 Jul 1999, Dann Pigdon wrote:

> As far as the arctic geese are concerned, arctic summers are very
> brief so many plants grow and bloom rapidly at about the same
> time, providing a sudden abundance of food that is highly predictable.
> Lack of predation is probably just one of the advantages of nesting
> in a polar or sub-polar region.

This must be true, of course.  However, I argue it is a prime advantage.
here are my reasons.  Some goose species nest in areas where there is
little food (see reference in earlier post).  Indeed, their anorexia is
apparently an adaptation to _low_ or unpredictable food supply available
to vast numbers of birds! Also, if food were a prime concern, and not
predation, one would expect nesting sites to be in more temperate regions
where there is lots of food.  Why then, do they not nest in these places.
The reason for this is straightforward: given the choice between food and
no predators, and food and plenty of predators, the geese have, by and
large, opted for low predator density.  It is very expensive to fly to
these places.  And, in cases where geese have found themselves on islands
without predators--tropical places, they have on occassion lost the
ability to migrate.
This also suggests it is the predators which select for long distance
flight.

I agree that this is a difficult issue and that specific adaptive
"reasons" may be be complex, obscure, and numerous.  I also agree that
different species may have very different reasons for migrating.  But
geese have several things in common which makes migration an imperative.
They are large, ground-laying, noisy and really obvious to those who would
eat them.  In non-nesting times this is OK: they can simply fly to some
other foraging site when a predator comes along.  But in nesting season
they cannot do this without losing their eggs.
In this sense they are like hadrosaurs.  But hadrosaurs can't fly to
remote places.  They and the dinosaurs that would eat them were relatively
homogenous with regard to locomotory ability.  My guess, then, is that a
hadrosaur colony served a very different function than a goose colony.