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.