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<DIV><FONT size=2>Hali
Angus, the basic conundrum behind your question is correct, but you
have the details backwards.
The migration-experienced monarchs that migrated all the way to
Mexico the year before, and overwintered there on about 3 isolated
mountain peaks, finally migrate back towards E. USA and E. Canada, but
never get there/here. They stop around N. Texas, lay eggs, die, and
the generation thus produced there, early, then continues on to migrate
further N-E, but again usually stops somewhere (forget where), breeds,
lays eggs and dies. It's the 3rd (or sometimes the second) generation
that finally makes it to eastern seaboard and breeds here. The 3rd
generation ones emerging here are therefore two generations away from
having any experience of migration, yet manage to migrate all the way
back to Mexico in one hop, to overwinter and start the cycle again.
The obvious interesting conclusion is that these monarchs have an
innate (built-in), so far unknown-for-sure guidance system, since they
obviously haven't experienced the migration route all, neither do they
have experienced parents to guide them (parents are all dead). The
situation is different for a western race that migrates up through
California as far as North B.C., I think in one hop (forget the
details).
The world authority/reseacher on this is Lincoln Brower, who gave an
excellent lecture in Dalhousie-Biology a few years back. He is
concerned about and involved in conservation efforts in the few
overwintering mountains in Mexico, which are gradually being logged
illegally, threatening the habitat and therefore the whole eastwards
migratory monarch system. Logging opens up gaps in the trees which
otherwise provide excellent still-air insulation. Monarchs on the edges
of the gaps get wet in rain, then freeze up at night and die in droves,
while those on protected dry branches still survive (for now).
Steve
On 27-Sep-06, at 1:42 PM, Angus MacLean wrote:
> Hi Jim and all:
> As I understand it current knowledge has it that "our" Monarchs do
> not reach the Mexican mountains but actually fly a distance south
> before laying eggs, etc. and their offspring continue the journey,
> perhaps having to repeat the process before that line of Monarchs
> reach their wintering grounds. Is this correct?
> Angus
>
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