butterfly migration

[Morten Dewald Drøgemüller Hansen]

Hi Leps-netters

The discussion about butterfly migration is very interesting. However, I think
that too much debate concerning the definition of the terms "migration" and 
"dispersal" may confuse rather than clarify.

I think that when we have a more or less unidirectional movement (Red Admirals
or Monarchs), it's migration. You can't say that the Painted Ladies DISPERSE
if they only fly towards N.... 

How long the Red Admirals migrate in spring depends partly on the wind 
conditions. If the winds blow from south, the butterflies may overcompensate
and fly too far north, and their offspring won't be able to return. The 
offspring of individuals which did NOT overcompensate may return to southern
Europe, thus making the "migratory genes" persist in the population. (I suppose
that people agree upon a genetic basis of migrations).

In Denmark, we see return migrations of Painted Ladies and Red Admirals every
autumn, but I don't think they can reach southern Europe. 

best regards
***************************************
* Morten D.D. Hansen                  *
* Dept. of Zoology                    *
* Institute of Biological Sciences   *
* University of Aarhus                *
* DK-8000 Aarhus C                    *
* Denmark                             *
* e-mail: dd at mi.aau.dk                *
* homepage: http://www.mi.aau.dk/~dd/ *
***************************************