An agricultural baler includes a bale chamber for the compression of crop material into bales. The bale chamber has a floor that comprises an inlet opening. The baler also has a plunger for forcing the crop material from an inlet end of the bale chamber towards an outlet end, and a feeder duct communicating with the bale chamber through the inlet opening. The feeder duct has an upper end facing generally upwardly and communicating with the inlet opening in the bale chamber and a lower end facing generally in a forward direction. The feeder duct also has a top wall and a bottom wall extending between the lower end and the upper end of the feeder duct. The baler also has one or more actuators that are configured to move the top wall and/or the bottom wall； and a controller configured to activate the one or more actuators during a baling operation in order to adjust the volume of the feeder duct.
