Chuck,
There was an article on how laboriosa overwinter in the valleys, and with clu
ster temperature actually lower than ambient in the day, by Underwood.
I think it is on Natural History. sometime in 1991.
I also remember reading about the same bee in Nat His. during the meeting of
New Orleans, so maybe Dec 1990, or Jan 91, but I am not sure if that is the on
e about migration during winter.