MESA, Ariz. -- The Cubs weren't the first team to move starting pitchers to the bullpen full time, but they definitely had success doing so in 2015 with Travis Wood, Clayton Richard and Trevor Cahill.
Manager Joe Maddon knows a little bit about such conversions. He switched Wade Davis, now the Royals' successful closer, to the 'pen when they were together in Tampa Bay.
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Pitchers and catchers officially report on Friday to the Cubs' camp, with the first workout scheduled for Saturday, but pitching coach Chris Bosio has been busy with bullpen sessions for at least two weeks. The biggest competition the Cubs will have this spring concerns who will be in the bullpen on Opening Day. There are plenty of choices.
Besides Wood, Richard and Cahill, the list of returning relievers includes closer Hector Rondon, Justin Grimm, Neil Ramirez and Pedro Strop.
Among the new guys on the roster are Adam Warren, acquired from the Yankees in the Starlin Castro trade. The 28-year-old righty went 6-6 with a 3.66 ERA in 17 starts, and he posted a 2.29 ERA in 26 relief outings. Warren was one of the early birds in Cubs camp.

The Cubs also added two lefties, Rex Brothers and C.J. Riefenhauser, who was claimed off waivers from Baltimore last week. Brothers, 28, has held lefties to a .224 average in his career. Riefenhauser, 26, has spent parts of the past two seasons in the Majors with the Rays, going 1-0 with a 6.30 ERA in 24 appearances. He recorded a 2.86 ERA in 29 appearances for Triple-A Durham in '15, fanning 34 batters in 34 2/3 innings while walking only seven. Also in the mix is right-hander Spencer Patton, 27, who compiled a 9.00 ERA in 27 relief appearances with the Rangers, and a 1.67 ERA in 26 games at Triple-A Round Rock.

Among the non-roster invitees: Jonathan Pettibone, 25, is coming back from multiple right shoulder surgeries. Lefty Jack Leathersich, 25, posted a 2.31 ERA in 17 relief appearances with the Mets in '15, while Jean Machi, 34, held left-handed batters to a .160 average pitching for the Red Sox. Southpaw Edgar Olmos, who was designated for assignment to make room for Riefenhauser, could be a non-roster invite if he clears waivers.

Maddon feels a team can never have enough quality pitchers in the bullpen.
"My concept is having at least four 'even or ahead guys,' meaning you have a relief pitcher who comes in the game and pitches comfortably when the score is tied or you have the lead," Maddon said. "There are a lot of guys who can pitch really well when you're behind. Those guys are nice to have to suck up some innings when things aren't going that well.
"When things are going well, which you anticipate to happen a lot this year [with the Cubs], you want 'even or ahead guys.' I believe we'll have seven guys in the bullpen who can pitch with the lead -- we're that good, we're that talented."
Cahill turned down a two-year deal with the Pirates and a chance to return to the rotation to stay with the Cubs. He posted a 2.12 ERA in 11 relief appearances last season with Chicago. Wood began '15 in the Cubs rotation (2-2, 5.06 ERA in nine starts), then was moved to the 'pen and compiled a 2.95 ERA in 45 appearances.

"We have guys who have four pitches, some guys five," Bosio said. "Other teams coveted guys we had, but they wanted to come here because they're comfortable with what we're doing."
And they'll get started this week.
Pitchers and catchers report
Friday
Full squad reports
Feb. 23
First Spring Training game
Away vs. Brewers, March 3, 2:05 p.m. CT
Opening Day
Away vs. Angels, April 4, 9:05 p.m. CT