Birkins isn't worthy of the 40-man roster spot. The 27-year-old lefty had a 6.61 ERA and a 1.64 WHIP in two starts and 52 relief appearances with Baltimore the last two seasons.
Birkins is 26 and has a career 7.85 K/9 along with 4.13 BB/9 and last year a 39% groundball rate. He's better against lefties, but uh...that's not saying much, at least in the majors, in the minors his splits were clear: .304 v. RHB, .145 V. LHB, YIKES! Last year he had an outing where he failed to record an out while allowing six earned runs.
I'm not sure if he's really worth a 40 man spot, but I know Raul Casanova isn't, and I'm guessing Jon Switzer will receive his walking papers soon enough.