Questions about migratory species

[GGrayWhite at aol.com]

I have been fascinated to read the recent notices about migratory butterfly 
species, but I wondered if one of you knowledgeable people could post a bit 
more about what is known of the migratory habits of butterflies other than 
Monarchs?  (Or list some source material.)  "Everyone" knows about the 
Monarchs, but it is relatively new information to me (and probably to plenty 
of other lay people and novice butterfliers) that other species migrate.  
Some questions I have are: What species migrate?  Do the same individuals 
make the flight south and then return in the spring? Do these butterflies 
overwinter in clusters like monarchs? Or just continue to breed and feed 
until the weather changes?  I'm sure I could come up with other questions as 
well.  Any information would be greatly appreciated!  --Grace Gray