Duchscherer has been limited during spring training because of stiffness in his surgically repaired left hip.
Jake Fox will be the backup catcher. Fox led the majors with 10 home runs this spring and Tatum batted only .216 in 13 games.
"Craig did some good things for us last year and will get an opportunity again if he takes care of his end of the bargain," manager Buck Showalter said. "He also has more important things going on in his life."
Tatum planned to leave the team to be with his wife, who is scheduled to give birth late this week.
Baltimore will carry both Brad Bergesen and Chris Tillman, who were supposedly locked in a duel for the third spot in the rotation. Either Bergesen or Tillman will start Sunday in Tampa Bay, and the other is expected to pitch on April 10, when the Orioles need a fifth starter.
Britton went 3-0 with a 1.35 ERA this spring, but if he stays in the minors for at least 20 days it will make him eligible for free agency in 2017 instead of 2016.
"I think he [was thankful] for the chance to come in, pitch, and the opportunity we gave him to take the ball," Showalter said. "He was impressive."
Information from The Associated Press was used in this report.