1320 



HORMONAL REGULATION OF BEHAVIOR 



rats are simultaneously given young mice 

 and rats to retrieve, they show some pref- 

 erence for the rats (Wiesner and Sheard, 

 1933). The common vole retrieves young 

 red-backed voles or field voles offered by 

 the experimenter (Frank, 1952). Cotton rats 

 adopt young laboratory rats (Meyer and 

 Meyer, 1944). Dogs readily adopt puppies 

 of other strains (Menzel and Menzel, 1953) , 

 and a polecat has adopted domestic kittens 

 (Herter and Herter, 1955). Kallmann and 

 von Frisch (1952) and Eibl-Eibesfeldt 

 (1958) have summarized observations from 

 many different sources which indicate that 

 many small mammals may adopt young be- 

 longing to different species, genera, and 

 even families. 



Rats will, however, not retrieve young of 

 all other species. Wiesner and Sheard ( 1933 1 

 offered pairs of 1- to 6-day-old rabbits and 

 rats simultaneously to each of 49 lactating 

 female rats, and found that 28 retrieved 

 both the young rat and the young rabbit 

 whereas in 21 cases only the rat was re- 

 trieved. In no case did the mother rat re- 

 trieve a rabbit while leaving the young rat. 

 Beach and Jaynes (1956b) report that rats 

 will not retrieve young guinea pigs, which, 

 of course, are much larger and more active 

 than 1- to 6-day-old rabbits or rats. 



In spite of the fact that they may re- 

 trieve young of other species, lactating fe- 

 males of at least some species of mammals 

 discriminate between their own young and 

 other young of the same species, and tend to 

 prefer their own young. When Beach and 

 Jaynes (1956c) tested 16 lactating female 

 rats in several situations in which the re- 

 trieving of their own young could be com- 

 pared with retrieving of other young rats 

 the same age as their own, all but one of the 

 mother rats tended to prefer their own 

 young. When "own" and "alien" young were 

 presented separately, there was a tendency 

 for the own young to be retrieved faster; 

 when the own and the alien young were pre- 

 sented to the mother rat together, there was 

 a tendency for the own young to be re- 

 trieved first. Wiesner and Sheard (1933) 

 had found no evidence of preference for re- 

 trieving of their own young, but as Beach 

 and Jaynes i)oint out, the earlier tests were 

 considerably less sensitive than the tests 

 used by them. Domestic mice, although they 



may retrieve alien young of their own spe- 

 cies, will often subsecjuently eat them 

 (Eibl-Eibesfeldt, 1950). When golden ham- 

 sters are offered strange young they often 

 eat them (Lauterbach, cjuoted by Eibl- 

 Eibesfeldt, 1958). Leblond (1937) points 

 out that domestic mice at first accept alien 

 young as readily as they do their own, and 

 that attachment to their own young de- 

 velops later. 



The stimuli on the basis of which mothers 

 recognize their own young may vary among 

 different types of mammals. In the Gala- 

 pagos sea lion, maternal care is restricted 

 to the mother's own young. Eibl-Eibesfeldt 

 ( 1955c) observed that mothers respond only 

 to the calls of their own young, and that 

 they apparently also recognize their young 

 by sniffing at them. In the case of the 

 American elk, on the other hand, Altmann 

 (1952) found that mothers reject strange 

 young on the basis of olfactory and prob- 

 ably also visual cues, whereas the calls of 

 any young are reacted to by many females. 

 Observations by McHugh (1958) indicate 

 that olfactory, visual, and auditory cues are 

 all used by female American bisons in iden- 

 tifying their young. 



Beach (1951) noted that considerable in- 

 dividual variability may be seen in the 

 laboratory rat with respect to recognition 

 of the young. Although some females con- 

 sistently retrieve their own young in pref- 

 erence to others, other individuals seem to 

 make no such distinctions. Similarly, Men- 

 zel and Menzel (1953) find that some fe- 

 male dogs only accept their own young, 

 whereas others will readily accept strange 

 puppies. It is not known whether such in- 

 dividual differences exist among nondomes- 

 ticated species. 



Although it may at first seem somewhat 

 contradictory to state that animals which 

 readily adopt young of other species are 

 capable of discriminating their own young 

 from other young of the same species and 

 age, the contradiction is more apparent than 

 real. Most of the experiments on "adoption" 

 of young of other species have involved the 

 presentation of the strange young under 

 conditions in which there was no possibility 

 of choosing between the alien species and 

 the mother's own species. Where such 

 choices are possible, the tendency to prefer 



