Hadrosaur nesting (long-winded response)

[Casey <tuckercj@muohio.edu>]

Hi gang!

Essentially migration occurs because of a need for food.  In Spring in
North America food is more readily available so migrating birds travel
back into the North to begin laying eggs & raising young.  Most
migratory species are insectivores & so must follow the insects into
warmer climes.  Most birds that do not migrate are either frugivorous or
granivorous.  Frugivores would be more prevalent in tropical
environments because plants species are not restricted to a specific
growing season in these areas, & granivores will be the prevalent group
in more northern climes because seeds are more readily available during
Fall & Winter in the North.  These granivorous species will supplement
their diet with insects in the spring, because they are readily
available & are a good source of protein, which growing chicks need a
great deal of.  Keep in mind that seeds are not readily available in
Spring because everything is budding & blooming, & so seed aren't
available yet.  Which brings me to the reason of why the insects are
migrating which is that they feed on the plant material & so they must
get it early in the growing season because as the plants mature they
build up their toxicity & structural defense mechanisms, & become
unedible for most insects.  The reason that the insects leave the
tropics is because the system becomes stressed with the influx of
insects, in addition to the resident insects that are already there
feeding upon the plant material.  So eventually the system reaches a
"carrying capacity" (for lack of a better word), & the migratory insects
leave for areas where food is more readily available without as much
competition, leaving the resident insects to utilize remaining food
sources, which are continuously replenishing themselves because of the
unlimited growing season (but they only grow so fast which is why the
migratory insects put a strain on the system).

Northern climates have quite a few avian predators including, but not
limited to, Raccoons, Opossum, Colubrid snakes, Owls, Falcons,
Accipiters, _H. sapiens_, cats, rats, squirrels, chipmunks, Icterids,
other aves (House Sparrows, Starlings, etc), weasels, & the list goes on
of the various species that prey upon not only adults, but eggs &
young.  So predator avoidance is not a good reason to migrate,
especially since many predators are coming out of hibernation (like
small mammals & snakes) during the Spring & are ready for the influx of
avian prey that is returning with the insects & plants.

Another thing to look at is that in Africa many herbivourous mammals
migrate.  Again, these migrations correspond to wet & dry seasons.  As
dry season sets in on one part of the continent, wet season sets in on
another so that it is a continuously cyclic event.  These herbivores
travel to where food is most plentiful, & they take with them a whole
host of animals that depend upon them including: insects, birds that
feed on the insects, carnivores that feed on the herbivores, scavengers
that feed on what's left of the herbivores, etc...  The only predators
that stay behind are the ones that are dependent upon water, like the
crocodillians which enter into aestivus during the dry season.  This
type of system seems like it would be a better model for the Hadrosaur
migratory pattern.  One in which the Hadrosaurs migrate in response to
plant availability in correlation to a wet season elsewhere,
Tyrannosaurids (predators in general) follow the hadrosaurs, & the
crocodillians (like Deinosuchus), remain in a state of aestivus.  Again,
this is just a model.  I, myself, am not familiar with the ecosystem of
the Hadrosaurian nesting sites, but would imagine that any migration is
in relation to food availability.

One other thing to point out is that Fall migration has already begun
for many bird species, & it's only July.

I hope this clears up a little bit about reasons for migrating.

Casey Tucker
dept. of Zoology
Miami University
Oxford, Ohio


S.P. (Shameless Plea ;-)

I'm currently searching for graduate schools in Avian paleobiology &
systematics .  If you are someone, or know someone, who might have an
opening for me please feel free to contact me.  I'm in the application
process right now for several schools, but I'm always looking for
others.   I hope to enter into a program in January as I am completing
my last semester of my undergraduate carreer this coming Fall.



********************************************************************
B.Dol@skn.sc.philips.com wrote:

> > Date:          Wed, 28 Jul 1999 11:48:07 -0400
> > Reply-to:      larryf@capital.net
> > From:          "Larry Febo" <larryf@capital.net>
> > To:            <B.Dol@skn.sc.philips.com>
> > Cc:            <dinosaur@usc.edu>
> > Subject:       Re: Hadrosaur nesting strategy...(was Re: The Life of
> Birds- Pa
>
> >
> > ----- Original Message -----
> > From: <B.Dol@skn.sc.philips.com>
> > To: <larryf@capital.net>
> > Cc: <dinosaur@usc.edu>
> > Sent: Wednesday, July 28, 1999 10:19 AM
> > Subject: Re: Hadrosaur nesting strategy...(was Re: The Life of
> Birds- Pa
> >
> >
> > > So wouldn't it be more logical to assume that the reasons for
> > > migration are not avoiding predators, because in another area
> there
> > > will always be other predators...maybe not that many or directly
> > > threatening, but they could in time evolve that way.
> > > Just a thought.
> > >
> >
> > 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.
> >
> > It was suggested to me (offlist) that more abundance of food was the
> reason
> > for bird migration. I thought food was always much more abundant in
> the
> > tropics, and therefore the ability to brood in a colder enviorn as
> > protection from cold-blooded predators would be the determining
> factor in
> > bird migration. Then again, not all birds migrate. How do the
> tropical
> > variety cope (with predators)?
>
> I'm not sure.
> Maybe because of the tropics more food is available so
> more offspring can be produced to ensure the species survival. It can
> also be that because of the abundance of food more offspring is
> produced than in 'colder' regions, but I honestly do not know if
> tropical birds have larger clutchsizes than other birds. That could
> lessen the need for migration.
> Maybe the surroundings allow for more and better hiding places and
> camouflage  making it more difficult for predators to actually find
> the prey.
> Maybe some other listmembers have some ideas about this too. This is,
> in my humble opinion, an interesting topic. Understanding the reasons
> for migration might give some insights into the possibilities of
> dinosaur migrations.
>
> >
> >