Actually over the course of a season, BB's are remarkably consistent.
Willy Taveras BB totals over the last 4 seasons: 25, 34, 21, 36.
Consistant and extremely poor. By comparison Adam Dunn, since someone brought him up: 114, 112, 101, 122.
Dunn had 6 more BB's last year than Taveras has in his career.
BB totals from month to month can fluctuate just like BA can. However, high BB guys are less susceptible to slumps, because even when they aren't hitting the secondary skillset of taking a BB is less affected. Taveras doesn't have that secondary skillset. Two things have to fail for a Dunn to hurt the club. All Taveras has to do is be Taveras. His whole game is BA. When that slumps, he's just an out machine that offers nothing on defense.