An agricultural baler (1) includes a bale chamber (9) for the compression of crop material into bales. The bale chamber (9) has a floor that comprises an inlet opening (19). The baler (1) also has a plunger (7) for forcing the crop material from an inlet end of the bale chamber (9) towards an outlet end, and a feeder duct (423) communicating with the bale chamber (9) through the inlet opening (19). The feeder duct (23) has an upper end (427) facing generally upwardly and communicating with the inlet opening (19) in the bale chamber (9) and a lower end (429) facing generally in a forward direction. The feeder duct (423) also has a top wall (435) and a bottom wall (437) extending between the lower end and the upper end of the feeder duct. The baler also has one or more actuators (440) that are configured to move the top wall (435) and / or the bottom wall (437)； and a controller (442) configured to activate the one or more actuators (440) during a baling operation in order to adjust the volume of the feeder duct (423).
