Avoidance of a return to the first component of a chain from the terminal component.

Three pigeons were trained on a chained fixed interval-fixed ratio schedule. Avoidance behavior which postponed a return to the first chain component from the second component was maintained on a second response key concurrently with the second component. When the fixed interval length was increased, avoidance rates first increased and then decreased as a function of fixed interval length. As the fixed ratio requirement was increased for one subject, avoidance rates first declined and then increased at larger fixed ratio values. Avoidance behavior maintained by postponing the first chain component was similar to avoidance behavior maintained by postponing a time out period.