Oley, N. N., Slotnick, B. M. 1970. Nesting material as a reinforcer for operant behavior in the rat. Psychonomic Science 21, 41-43.

Rats will readily work for the acquisition of nesting material. Paper strips serves as an adequate reinforcer. .. Prior to parturiation, only a small daily nest was built and barpressing occurred only in the dark part of the lighting cycle. Following parturition, barpressing for nesting material greatly increased.