PARENTAL BEHAVIOR 



1321 



young of the iiiothei-'s own species is readily 

 seen. 



D. NURSING AND SUCKLING BEHAVIOR 



In discussing the l)ehavioral and physio- 

 logic aspects of mother-young relationships 

 centering around feeding, I shall use the 

 terminology suggested by Cowie, FoUey, 

 Cross, Harris, Jacobsohn and Richardson 

 (1951). "Nursing" means behavior on the 

 part of the mother which fosters access to 

 the nipples by the young. "Suckling" is the 

 activity of the young animal sucking the 

 nipple. "Suckling stimulus" is the sum of 

 the stimuli applied by suckling. 



1. Behavior of the Nursing Mother 



The duration of the period of lactation, 

 which starts about the time of parturition, 

 varies considerably in different species. The 

 young of some species of rodents may feed 

 independently of the mother by the time 

 they are 10 to 14 days old. In other species 

 the nursing period is much longer. Herd- 

 living animals usually nurse the young for 

 several months, whereas some aquatic 

 mammals, such as the sea lions, may con- 

 tinue nursing for up to a year. These differ- 

 ences in duration of the nursing period are, 

 in part, correlated with the conditions of 

 the animal's life. The young of mammals 

 which live in burrows are usually able to 

 get food without the help of the mother by 

 the time they are old enough to leave the 

 burrow; grazing herd-living types tend to 

 remain with their mothers in the herd for 

 a much longer time. The differences in kind 

 and duration of the mother-young relations 

 in these two types of mammals are un- 

 doubtedly relevant to the differences in 

 gregariousness which characterize them as 

 adults (Krumbiegel, 1955). This rather 

 general statement is about as far as we can 

 go, because detailed studies of mother- 

 young relationships, suitable for compara- 

 tive analysis, exist for only a few mam- 

 malian species. 



I have already pointed out (see al)0ve, 

 p. 1312) that the establishment of a nursing- 

 suckling relationship between mother and 

 young is a mutual affair, depending on the 

 behavioral characteristics of both partici- 

 pants. Changes in both the mother and 

 young also contribute to the changfintr i-cln- 



tionships during the later stages of lacta- 

 tion. The best and most detailed analysis 

 of such a relationship is to be found in still 

 unpublished studies on the domestic cat 

 carried out by Rosenblatt, Wodinsky, Tur- 

 kewitz and Schneirla, at the American Mu- 

 seum of Natural History, and partially 

 summarized by Schneirla (1956, 1959). 

 These workers found that the kittens begin 

 to discriminate among the mother's nipples 

 very shortly after birth. Significant and 

 persistent preferences of individual kittens 

 for specific nipples can be detected before 

 they are 2 days old (Ewer, 1959). In the 

 early days of the kittens' life, nursing epi- 

 sodes tend to be initiated by the behavior 

 of the mother, whereas later nursing epi- 

 sodes are initiated by approaches of the 

 kittens to the mother. The transition is not 

 entirely gradual, but occurs fairly abruptly 

 between the 18th and 27th days after birth. 



The mother domestic cat, like many other 

 animals, spends most of her time with the 

 young during the first few days after par- 

 turition. Depending on the species, other 

 patterns are also found. The domestic rab- 

 bit and European hare, for example, visit 

 the nest only to nurse the young, leaving it 

 at the end of the nursing episode (Cross and 

 Harris, 1952; Krumbiegel, 1955). Bartholo- 

 mew and Hoel (1953) found that mother 

 Alaska fur seals stay ashore with their 

 young for 1 to 3 days, then leave and stay 

 at sea for 3 to 10 days (Bartholomew, 

 1959). 



Tiie decline of lactation is associated with 

 changes in nursing behavior. The time spent 

 on the nest by domestic mouse mothers de- 

 creases from parturition to about 15 days 

 postpartum, and this decrease is paralleled 

 by a decrease in the average length of the 

 nursing episode (Bateman, 1957). Similar 

 observations have been made on dogs which, 

 as lactation declines, assume the nursing 

 liosture less and less frequently (Martins, 

 1949). Hafez (1959), in a brief report, 

 states that day-to-day variations in nurs- 

 ing intervals in the domestic pig are small 

 compared with the individual differences 

 between animals. 



'£. ^filk Ejection 



The physiology of milk ejection and of 

 lactation are fully discussed in the chapter 



