In her semi-annual testimony to Congress, Fed Chair Yellen said that the Fed expects that economic progress will call for "further gradual increases" in the federal funds rate. She also said that it would be "unwise" to wait too long to hike rates. Yellen later added that the Fed will consider in coming months when to begin to reduce the Fed's holdings of MBS. Of note, she said that the Fed will not sell MBS to shrink the holdings, but rather will stop replacing principal reductions. The expected pace of tightening by the Fed increased a little after her testimony, causing MBS to decline.