I don't imagine the Bucs will give anything up for him, or hopefully not, but this seems a strange move. We have Argenis Diaz at AAA, and Cedeno and Crosby at the ML level. So unless this is a precursor to a trade, which also seems strange, I don't know what the reasoning here is.
UPDATE by Charlie: I don't get this, either. Brian Friday, too, is on a rehab assignment and will be back with Indianapolis soon. Dejan Kovacevic writes that the trade is merely for "future considerations," which essentially means the Bucs get Bixler for free, but still... he's horrible, and I don't know why the Pirates would waste their time with this.