Sylvester, who turns 26 on Friday, was a fifth-round pick of the Pittsburgh Steelers in 2010. He played in 50 games in four seasons with the Steelers, making two starts. He should compete with Ty Powell and rookie Randell Johnson for a role on special teams.
To make room for Sylvester on the 90-man roster, the Bills waived tight end Mike Caussin, who missed each of the past two seasons with injuries. Caussin had been with the Bills since 2010.
In a procedural move, the Bills placed Alonso on the active/non-football injury list. Alonso remains on the 90-man roster and can be taken off the list at any time. The Bills may later choose to place Alonso on the reserve/non-football injury list, which would keep him out of at least the first six weeks of the regular season. He isn't expected to play this season.
The Bills also placed Johnson and cornerback Leodis McKelvin on the active/physically unable to perform list. Johnson participated fully in spring practices while McKelvin was recovering from hip surgery. Either player can come off the list at any time.