Mountcastle was called up to Double-A Bowie on Thursday, Steve Melewski of MASN Sports reports.
Mountcastle will make his first start with Bowie at third base against Altoona on Thursday. The 20-year-old was hitting .314/.343/.542 with 15 home runs and 47 RBI during 88 games with High-A Frederick upon his promotion. Mountcastle will get a chance to see how he stacks up at the next level, with a spotlight on his K:BB that was sitting at 61:14 during his time with Frederick. The top prospect will need to improve on those numbers in order to continue his progression for the Orioles.