What are the duties of a district court in connection with a Report and Recommendation of a magistrate judge?

The duties of the district court in connection with a Report and Recommendation of a magistrate judge are set forth in Federal Rule of Civil Procedure 72(b) and 28 U.S.C. 636(b)(1). The district court must "make a de novo determination of those portions of the report . . . to which objection is made[,]" and "may accept, reject, or modify, in whole or in part, the findings or recommendations made by the magistrate judge." 28 U.S.C. 636(b)(1); see also United States v. Remsing, 874 F.2d 614, 617 (9th Cir. 1989). The district court need not review de novo those portions of a Report and Recommendation to which neither party objects. See United States v. Reyna-Tapia, 328 F.3d 1114, 1121 (9th Cir. 2003) (en banc) ("Neither the Constitution nor the [Federal Magistrates Act] requires a district judge to review, de novo, findings and recommendations that the parties themselves accept as correct.").