By Joseph Santoliquito

PHILADELPHIA (CBS) — There’s no mystery here as to why the Eagles fell apart late last season. One of the glaring drawbacks was the secondary. In the crippling 27-24 loss to Washington on December 20, the Eagles gave up 55- and 23-yard passes. Former Eagle DeSean Jackson ravaged the Birds, averaging 31.5 yards a catch.

Philadelphia ranked 31st in the NFL in pass defense in 2014, giving up 4,238 yards passing. The only team worse was Atlanta, which gave up 4,478 passing yards. Compounding that was the fact that the Eagles gave up 72 pass plays that went for 20-plus yards, the most in the NFL (Chicago came a distant second at 65), and 18 plays of 40-plus yards, another NFL high.

So on the second day of training camp, Eagles’ defensive coordinator Billy Davis openly admitted something about last year’s cornerback tandem of Cary Williams and Bradley Fletcher.

“I have this beautiful view of hindsight right now that when you’re in the middle of it, you don’t quite have it, and as it works out and plays out against you, you kind of say to yourself, ‘I kind of made a mistake there.’ At the end of the Giants’ game, ‘Fletch wasn’t on the field, and we still had some issues,” Davis said. “We had to work through it and we made the best decision we could at the time, watching every snap of practice. Maybe we over analyzed it. You have to make those hard decisions and hopefully most of them work out.”

This season, Davis is counting on the influx of rookies JaCorey Shepherd, Eric Rowe and Randall Evans to possibly make an immediate impact, along with free agent Walter Thurmond, maybe teaming with Malcolm Jenkins at safety. Davis says there is depth in the secondary, and Nolan Carroll will also be a key, coming off the best off-season anyone had on the team.

“Nolan has all of the skillsets to start, and he did in Miami,” Davis said. “He had one of the best off-seasons that I’ve been around. We viewed him as a starter last year, and early on, we tried to rotate him in, [but] he had some hamstring issues. I didn’t get him in there and I probably should have. That’s on me. We have all the confidence Nolan can compete for that other starting corner spot [across from free agent signee Byron Maxwell]. We’re excited about Nolan.”

This newfound secondary depth that both Davis and Eagles’ head coach Chip Kelly spoke about is a reason why the Eagles traded proven nickel corner Brandon Boykin to Pittsburgh on Saturday for a conditional fifth-round draft pick in 2016.

“I was a Boykin fan and I always liked Brandon,” Davis said. “He did a good job in nickel for us. I coached the nickels the last few years and I got to know him better than some of the other positions. But the competition and depth, because it’s become closer, when someone comes asking for a trade, it was close in depth where we thought it was good enough for both of us. We didn’t want to lose him. Pittsburgh kept coming and coming.”

Shepherd took the first-team snaps as the nickel, replacing Boykin. Davis said that had more to do with a rotation.

“It’s not the first team, second team, third team, it’s groups that we’re going to practice in, and we’ll mix and match and move everyone around,” Davis said. “We have multiple positions that can move around. We have guys that can play corner, safety and nickel, or corner and nickel, or safety and corner, and we’ll move them around. Everyone is going to get in and we’ll take a look. Maxwell, with Nolan and Rowe will stay outside at the corner spots, with Nolan jumping into some dime.”

Davis said the Eagles always wanted to be a press team last year, and try to reroute the receivers.

“The biggest change that’s happened this off-season is the technique, and the emphasis on Technique, not that we’re saying we’re going to press more, we’re just spending more time on the press technique so we can get better at it than we were a year ago,” Davis said. “That was one of our big flaws was that our press technique wasn’t where it needed to be.”