monarchs and swan plants
Paul Cherubini
paul at concentric.net
Tue Jan 19 06:03:59 EST 1904
John Grehan wrote:
> It was my understanding that the monarch was already in NZ and Australia
> before human introduction of the host-plant, but that they were not able
> to permanently establish in the absence of the hostplant. I also understand
> that there is no migration phenomenon like that in America - is that correct?
A monarch biogeographer, Richard Vane-Wright has studied the situation in detail and
found the monarch became established in Hawaii and many other central and south
Pacific islands is the mid-late 1800's. This timing coincides with the advent of fast
moving steam powered trading ships. It is interesting to note that the areas in Australia
where the weedy swan plant became established are the same areas where the native
eucalyptus forests were clear cut to accomodate agricultural interests.
The seasonal migration/overwintering phenomenon in Australia is just like that in America
except the numbers of butterflies involved and the distances they travel are smaller. Right
now is late autumn in the Sydney area and hundreds of monarchs can be found clustering
in at least a dozen eucalyptus groves slightly west (inland) of the city. Clustering also
occurs in New Zealand at this time of the year, but the migration there has no been
studied in detail.
Paul Cherubini, Placerville, California
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