Migration imperative

[Lyril]

I'm in south-eastern Australia. Monarchs (we call them Wanderers) have been in this country since the 1820s and have spread wherever Asclepias sp. grows, as in other countries. But little is known about where they over-winter, or their migrations, if indeed they do.
I watched the tv show Great Migrations' last Sunday and was astounded by the Monarch segment. I knew they migrated of course but I didn't know that it is so much a part of their genes - hard-wired, so to speak. That each summer generation goes a bit further north, and the very last generation flies all the way back to Mexico.

My questions: do any butterflies stay in one area? I noticed a west coast population on the map; do they fly to the same northern destinations and return to their original sites? Are there any sites where they are permanent residents and don't go through that enormous journey?

In other countries where they've settled, like Australia, a northern migration wouldn't make much sense, especially in Western and South Australia. I believe our summer populations come from South Australia, due west about 500km, but no-one knows where they go in autumn. The populations in New Zealand would have a much shorter journey. It must therefore be possible for a hard-wired imperative like the urge to migrate north to be cancelled somehow! Is this possible? They've only had about 180 years here which isn't very long.

Are insects as adaptable as that?

[Lyril]

Correction: they've were sighted first in 1871, 140 years ago, not 1820s. Faulty memory!

Also we have an Australian species known as the Lesser Wanderer (Danaus chrysippus petilia) which is smaller but the caterpillars and pupae are quite similar, though the pupae can be pink. This prefers Asclepias plants even though these are not native to Australia. Its original food plant is Cynanchum but it prefers milkweed. Reasonably common in summer, with the larger Wanderers.

[Mona Miller]

I think your Monarch goes where there is food. It follows seasonal patterns for its host plant. They do a bit of migration in New Zealand. Leaving breeding/host plant areas and spending some time wintering over, but the areas they winter over have to provide food, water, and shelter.

Have you checked out the Monarch Butterfly NZ Trust:
http://www.monarch.org.nz/monarch/

Your Lesser Wander looks like out Queen or Soldier. The Soldier prefers the Cynanchum (Honeyvine).

http://www.butterfliesandmoths.org/spec ... s-gilippus
Queen, Danaus gilippus

http://www.butterfliesandmoths.org/spec ... s-eresimus
Soldier, Danaus eresimus

[Paul Cherubini]

I'm in south-eastern Australia. Monarchs (we call them Wanderers) have been in this country since the 1820s and have spread wherever Asclepias sp. grows, as in other countries. But little is known about where they over-winter, or their migrations, if indeed they do.

In the temperate zone latitudes of Australia (roughly higher than 32 degrees S) and elsewhere around the world most monarchs enter reproductive diapause in late summer or early fall (March & April in Australia) and migrate to overwintering sites.

In Australia, because there are so many eucalyptus trees and only dozens to hundreds of monarchs in any given area instead of thousands, it can be hard to locate the overwintering sites, but they are there and quite widely scattered. Some are in the Adelaide area, for example, and on Flinders Island inbetween Australia and Tasmania. And lots of cluster sites can be found in the hilly pasture country slightly west and southwest of Sydney. I don't know of anyone who has looked for sites in Victoria, Australia.

[Mona Miller]

http://books.google.com/books?id=H5nRqh ... &q&f=false
The monarch butterfly: biology & conservation By Karen Suzanne Oberhauser, Michelle J. Solensky
Search on "Australia", this book has several references to migration in Australia.

http://jeb.biologists.org/content/199/1/93.full.pdf
MONARCH BUTTERFLY ORIENTATION: MISSING PIECES OF A MAGNIFICENT PUZZLE
LINCOLN P. BROWER
Search on "Australia"

[Lyril]

Thanks for the information. The NZ forum has a terrific paper on the discovery of the migratory habits of US butterflies which I pored over yesterday:

http://www.monarch.org.nz/monarch/wp-co ... brower.pdf

Fascinating stuff. So it seems they may be opportunistic migrants in many places - migrating when necessary. I wonder when and why the really amazing long migration (Mexico to northern US) began and why it became a biological imperative. I suppose this will never be known.

Such amazing creatures.

[Paul Cherubini]

The migration to Mexico was much shorter during the Ice Ages because milkweed grew as far north
as roughly Texas or Oklahoma. Minnesota and the Great Lakes States were covered with glaciers. Then as the world warmed, milkweed advanced further and further north and the monarch followed it.