Donna,
I am so glad you posted that A/B picture of their "whispers!"  I saw it but didn't know how to post!  I have to admit, it is pretty darn cute!  
I wonder what drives them... how they leave each other and then meet again.  I always wondered where Kaver went after he would leave.  I wonder where he is now.... ???
jeanne, I think me and you are on the same circuit...I'm so darn curious about all this migration stuff that I just want to get into one of their heads and find out.  

 Do they just say "well, gotta go"? IDK. pffft.