Deliver of an offspring is just a start toward propagation of a species. Mammals require considerable postnatal care to survive - so they can eventually reproduce themselves.
Maternal responsiveness. Periparturient behaviors can consist of seeking seclusion, nest-building, retrieving and grooming of the young, nursing posture, and protective aggression. Induction of maternal behavior is associated with the time of parturition, but not the actual event, or suckling stimulus that might ensue. Maternal instincts are not negated following delivery by cesarean section or lack of nursing. Pseudopregnant animals sometimes exhibit behaviors typical of late pregnancy.
Hypophysectomy does not prevent maternal behavior - pointing toward a predominant neural component in responsiveness. Lesions placed within the neocortex or hypothalamus eliminate behavioral responses. The role of hormones is to shorten the timing of the onset and to increase the intensity (quality) of maternal behaviors (ie., to set up the neural mechanism). Once maternal behavior is initiated, it can be sustained throughout the postpartum-weaning interval independent of endocrinological influences. Hormonal amplifiers of maternal responsiveness include prolactin, placental lactogen, oxytocin, and estradiol; inhibitory modifiers include progesterone and the endogenous opiates (both of which normally decline postpartum). Postpartum depression and irritability in women have been related to hyperprolactinemia.
A decline in body temperature (a hypothalamic-regulated process) of the dam will elicit maternal responses; this occurs when the mother comes into contact with her (chilled) newborn.
Neonatal bonding/surrogacy. Mutual identification by mother and newborn entails the processing of multisensory information. Auditory signals are used for recognition at a distance. Olfactory and visual cues become important once contact is made. Licking of the newborn by the dam is customary in some species (Figure 5-37).
Foster care for conspecific alien young is sometimes furnished by lactating females (circumstances in which this might occur vary widely between species). Bonding between mother and newborn (related or not) must occur within a critical period of approximately 12 hours postpartum in sheep; thereafter, the ewe will usually reject the lamb. Pigs and primates are relatively tolerant of alien young. Lactating lionesses will allow unrelated cubs of their pride to suckle indiscriminately; soon after birth it often becomes difficult to identify the genetic mother (Figure 5-38). Neonates generally do not show a strong preference from whom they receive nourishment.
Care provided by nonlactating females is also observed in the wild. Female elephants are known to stand guard, as if assuming the role of midwives, as the cow-elephant gives birth and provides immediate attention to her calf. Juvenile females are most likely to help with the daily routine care of the young.
Maternal behaviors can be conditioned in virgin and nulliparous females - this is done by repeatedly subjecting the female to newborn. Lactation can actually be initiated in primates as a result of exposure to young and(or) mammary stimulation. Previous experience (primiparous females) decreases the latency time necessary to become sensitized and accept alien young.
Paternal care. Significant parental care provided by the male is rare among mammals - exceptional cases include gerbils and some species of primates. Male marmoset monkeys assume the major role in infant rearing (outside of periodic nursings provided by mom). Paternal care normally involves foraging or hunting for food and protection. The male gorilla will remain faithfully at the base of a tree his family has taken as residence and fend off predators (he is often too heavy for arboreal life himself).