The ability of pigeons to maintain a constant operant response rate, despite changes in the force required to operate the key‐mechanism, is discussed from a servoanalytic standpoint. It is shown that a first‐order linear feedback control system can account for the behaviour observed when a critical force requirement is not exceeded. Beyond the critical value the pigeons do not maintain the constant rate; and thus the control system is no longer linear. The existence of a limit to the applied force can account for this behaviour in this latter condit