*In Britain (and maybe elsewhere) Vivian -- or Vivien -- is also a male name. Interesting how times & tastes change, eh?
*True.  That is probably because it is originally French:  Vivien (masculine) and Vivienne (feminine).   Because English doesn't have grammatical genders (unaccountably confused with biological sexes, for the last forty years), "Vivian"  was a logical anglicisation of both forms.   "Vivien" as a girl's name is a little pretentious, however, and a lot daft, although I think that that was how the late Mrs. Olivier spelled her forename.   There are others:  Lesley and Lindsey (although female Lindseys have always heavily outnumbered male, in my experience).   Names ending in "-ley", meaning "meadow", and "-sey", meaning (I am guessing) "island", look like classic English geographical names.    How they became female first-names is a mystery to me.   

Female Tristans, though?   Ermmm, no.