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A technique for the quantification of nest building in the rabbit is described. The doe is given access to a rack containing 48 small cans each of which contains a “wad” of excelsior. The rabbit will pull these wads out of the cans and will shred a number of them in constructing her nest. Analyses of the behaviour of 16 strain ACEP and 16 strain III rabbits found that the number of wads pulled and shredded reached a peak on the day that the pregnant females built their maternal nests. Seven control females failed to show any systematic trend in their shredding behaviour. The shredding score was also found to be independent of strain differences, amount of time spent in the maternity cage prior to parturition, and whether the mother was primiparous or multiparous.

Prior research has found that mice reared and nursed by a lactating rat mother or reared in the presence of a non-lactating adult rat (an ‘aunt’) gave a significantly smaller adrenocortical response to a novel stimulus than did control mice. Although the aunt studies eliminated the rat mother's milk as the critical variable, the experimental effect was not as profound as that originally observed using rat mothers. This may be because the rat aunt did not interact with the mice as much as the rat mother. In the first experiment we maximized the extent of the ratmouse behavioural interaction by using as an aunt a rat who had just given birth but was unable to nurse because her nipples had been previously removed (thelectomy). As hypothessized, the experimental effect was greater than previously obtained using other aunt preparations and approximated the effect obtained using rat mothers. There was no difference in body weight, but mice reared with aunts had a higher mortality rate between birth and weaning as compared to controls. In the second study experimental mice were reared by their natural mothers in the presence of a thelectomized rat (control aunt) or a thelectomized rat which had had immediate parturitional experience (post partum aunt), while control mice were reared by their natural mothers. Ratings of the maternal behaviour of rat aunts confirmed the a priori assumption that post partum aunts would be more maternal toward the mouse young than would control aunts. Mice reared with post partum aunts were found to be less active in the open field and gave a lesser adrenal corticosterone response to a novel stimulus as compared to mice reared with control aunts or control mice. In addition, within the post partum aunt group a significant correlation of −0·61 was obtained between maternal ratings and the adrenal corticosterone response of the mice. Further, the corticosterone response was positively correlated with openfield activity. The relevance of this latter finding to the interpretation of mouse open-field activity is discussed.