Studies on Maternal Retrieving in Rats: II. Effects of Practice and Previous Parturitions

Abstract

The maternal behavior of 19 multiparous and 18 primiparous rats was compared. Females that had previously born and reared litters did not differ significantly from primiparous animals in prepartum nest-building or cleaning of the young at the time of parturition. Some multiparous individuals had been given special retrieving tests during their first lactation period. Following a second pregnancy the retrieving behavior of these individuals differed in no appreciable way from that of other females which had just delivered their first litter. When multiparous and primiparous females were observed in a series of daily retrieving tests their behavior improved, and the course of improvement was the same for both groups. Various controls indicated that this improvement was not due to changing qualities of the growing young. Increased efficiency of retrieving could be traced to two kinds of change. The first consisted of a rather sudden decrease in the delay preceding the initiation of retrieving once a test had begun. This period of delay was marked in the first test but was greatly reduced on the second day and on all days thereafter. A second change involved a reduction in the amount of locomotor activity associated with retrieving. On successive tests the females tended to proceed more and more directly to the scattered pups and to retrieve them with a minimum of interpolated exploration of the cage.