LESSER WANDERER ( Danaus Petilia) A Mini Migration ?

I am always intrigued at the fragility of many of the creatures that cohabit this world with us and that they survive at all is nothing short of unimaginable .
One of these creatures are Butterfly's.
A few days ago I was fortunate to see something I don't recall seeing before, hundreds of Lesser Wanderers in a small area beside a dam.
 I think they may have congregated here to mate as some of them had very worn wings so were already some months old.
My Sister in law had arrived there a few days earlier and there were many more than I witnessed so many in fact that the branches of  the bushes the butterfly's rested on were bowed down with weight of these little light creatures
Up until

now I have only seen the Lesser Wanderer's one at a time in my garden and even out in the surrounding countryside, I have never seen more than one or two at a time and so had come to the conclusion that these beauties were in short supply, out in this dry countryside.
 So nice then to find that I am wrong .
One of my friends also saw a similar event out at one of the stations so no doubt they are happening everywhere at the moment. 
Could it be that our Lesser Wanderer's who are related to the famous Monarch butterfly of America also do a migration but not on such a grand scale !!
 I would love to hear from others regarding this thought