PARENTAL BEHAVIOR 



1315 



trieve young. Wiesner and Sheard (1933) 

 found that 19 of 21 primiparous rats tested 

 just after parturition showed the retrieving 

 response to the young, whereas of 21 preg- 

 nant nulliparous rats tested 1 to 7 days be- 

 fore parturition, only 4 retrieved young. In 

 another test, they found that only 6 of 34 

 pregnant nulliparous females tested 1 to 9 

 days before parturition showed any retriev- 

 ing behavior. Rowell ( 1960b) found that 

 ]iregnant and nonpregnant female golden 

 liamsters accepted and retrieved only 3 out 

 of 33 pups, in contrast to postparturitive 

 animals, which usually accepted and re- 

 trieved young pups. In a somewhat similar 

 series of observations Labriola (1953) of- 

 fered young rats to 10 nonpregnant nullipa- 

 rous females and to 10 females which had 

 given birth 24 hours previously. None of the 

 nonpregnant animals retrieved any young; 

 all of the postparturitive animals did. 



Herter and Herter (1955) found that a 

 pscudopregnant polecat retrieved domestic 

 kittens. Retrieving by pseudopregnant ani- 

 mals has also been noted in the domestic 

 rat (Herold, 1954) and in the dog (Lang, 

 1931). 



Retrieving, of course, continues during 

 the lactation period (Wiesner and Sheard, 

 1933). The data presented so far might sug- 

 gest that retrieving behavior is limited to 

 the period at the end of pregnancy and 

 the lactation period following parturition. 

 Unfortunately, the situation is not quite 

 that simple. About 20 per cent of domestic 

 rats retrieve regardless of sex or reproduc- 

 tive condition (Wiesner and Sheard, 1933; 

 Riddle, Hollander, Miller, Lahr, Smith and 

 Marvin, 1942; Riddle, Lahr and Bates, 

 1942). Frank (1952) found that males and 

 nonpregnant females of the common vole 

 often retrieve young, although not as often 

 as postparturitive females. Leblond (1938, 

 1940) presented young rats to 12 female 

 rats that were some 6 to 24 weeks past their 

 last parturition, and in which lactation had 

 ceased. Ten of the 12 animals retrieved, re- 

 trieving occurring in 90 per cent of the tests. 



Rowell (1960b) found that young golden 

 hamsters begin to retrieve younger pups as 

 soon as they are strong enough, and that 

 this retrieving behavior disappears with 

 the onset of aggressive l)ehavior, which ap- 



pears at different ages in animals reared un- 

 der different conditions. 



The incidence of retrieving behavior sug- 

 gests a parallel with that of nest-building 

 behavior. Both types of behavior are ob- 

 served to occur in the mouse starting at 9 

 or 10 days of pregnancy, whereas in the rat 

 the onset is later, closer to the time of par- 

 turition. Both types of behavior are also 

 seen in males and in nonpregnant females, 

 to a lesser degree, and to varying extents by 

 different observers, probably under different 

 conditions. Unfortunately, there does not 

 exist a good study of the correlation be- 

 tween these two types of behavior during 

 a normal reproductive cycle. The best stud- 

 ies of nest-building behavior, such as those 

 of Roller (1952, 1956), were done under 

 conditions in which retrieving was not 

 readily observed, and the best studies of re- 

 trieving, such as those of Wiesner and 

 Sheard (1933) and of Beach and Jaynes 

 ( 1956a, b, c) , w^ere done on animals in which 

 nest-building behavior was not being stud- 

 ied. In a number of other studies, nest- 

 building and retrieving were lumped to- 

 gether in order to construct a "maternal 

 behavior" score, which was then used with- 

 out further differentiation of its components 

 (Leblond, 1940). Closer study of the details 

 of variation between individuals, between 

 species, and during the breeding cycle 

 should be rewarding. 



Hormonal induction of retrieving be- 

 havior, (a) Hypophyseal hormones. Collip, 

 Selye and Thomson (1933) hypophysecto- 

 mized female rats shortly after parturition, 

 or later during lactation. Lactation ceased 

 and the mammary glands regressed, but re- 

 trieving and other aspects of maternal care 

 continued. Other observers have noted that 

 hypophysectomy does not interfere with re- 

 trieving behavior (Leblond and Nelson, 

 1937a; Obias, 1957), even though lactation 

 is suppressed (Leblond, 1940). 



Using a more quantitative approach than 

 the earlier investigators, Riddle, Lahr and 

 Bates (1942) found that hypophysectomy 

 actually increased retrieving behavior. In 

 both male and female rats, hypophysecto- 

 mized animals retrieved on 68 to 75 per cent 

 of the tests, compared with only 21 to 23 

 per cent for intact animals. 



The apparently contradictory results of 



