Extra-Hormonal Factors in Maternal Behavior

In rats and mice the main manifestations of maternal behavior are retrieving, licking, and cuddling of the young. Along with these activities, but often independent of them, may occur nest-building, defense reactions, and prolonged station on the nest. Nest-building, especially, is largely determined by body temperature 1 and other physiological factors 2 which do not seem to affect the principal forms of maternal behavior. The retrieving of young is the type of maternal behavior which lends itself most readily to objective measurement. It is different from mere retrieving of material to the nest since the latter is not accompanied by licking and cuddling. It is elicited in a mouse not only by its own young, but apparently to the same degree by any young of the species which are of the same age. The maternal behavior of the mouse was examined in 5-minute test periods with newborn young by a method previously described. 3 Only animals that had retrieved newborn in 2 test periods are reported as being maternal. Both normal and experimental animals were tested, the normals comprising virgin females, females during and after lactation, and males under 120 days of age; the experimental animals consisted of males castrated either at birth by Pfeiffer's method 4 or after puberty, males grafted with ovaries, and males injected with oestrin from birth on. The latter animals are comparable to hypophysectomized animals, at least as far as the gonads are concerned.