The parturient rat manifests a strong nest building tendency which is closely associated with the birth and care of her young. This wave of activity is stronger than similar nesting responses evokable by thermal deficiency in all rats beyond the age of infancy. It appears to be activated primarily by factors arising within the parturient female rather than from stimuli of the external environment. . . .

Primiparous females displayed nesting activities and responses directed toward the delivery, cleansing, suckling, and general care of their young that differed in no observed manner from those of multiparous animals. Likewise healthy blind and anosmic animals were not distinguishable from normal animals in these respects. . . .

Another phenomenon strikingly absurd from the layman’s point of view appears occasionally among parturient females whose nesting materials are adequate, but strictly limited in amount. During the evenings, especially, the female leaves the nest and busies herself in its repair or enlargement. From time to time she sallies forth to other parts of the cage in search of bits of shavings, paper, etc. Eventually there is nothing more to be had; nevertheless, the search continues. Then the female may go to the farther corner of the cage, turn partially around, notice her tail, pick it up in her mouth, carry it back to the nest, and deposit it on the nest materials. Sometimes it is pushed into place with her forepaws after it is dropped. Again she goes out on another search which ends as before in her "waltzing" back, tail in mouth. Such stereotyped responses may go on for a half hour or more in a single evening. In one pregnant female housed on a floor of hardware cloth and with no nesting materials, this act was repeated over and over again during the 12-hour period prior to parturition. Actions of this type strongly suggest to the writers the presence of a strong inner driving factor back of nesting responses which finds expression even though the normal provocative objects are absent and only poor "equivalents" are found. Fundamentally, the act is a perversion, if we use this term in its literal sense.1

1Sturman-Hulbe, M.n/an/an/an/an/a, and C.P.Stonen/an/an/an/a, "Maternal Behavior in the Albino Rat," , 9: 234, 235, 208–209.