NO. 3597 RODENT ETHOLOGY — EISENBERG 19 



as defined in the previously quoted monograph. It is the central 

 thesis of this section that a given species has a typical social organiza- 

 tion that falls into one of the three major categories. 



In order to describe quantitative differences among species, three 

 techniques have been employed: (1) the simultaneous or territorial 

 encounter; (2) the maintenance of pairs through parturition; and (3) the 

 study of groups derived from internal recruitment by births (see p. 26). 

 The species-specific social organization is a result of species difTerences 

 in the ability to tolerate contact ^^ith conspecifics. Thus, each species 

 has a social tolerance that, when exceeded, will residt in pathologies 

 such as failure of the female estrus cycle, abandoning or destroying 

 the litter by the mother, delayed maturation of the young, fighting 

 to the point of wounding or death, and failure of the male gonadal 

 development. The encounter allo^^'s one to make comparisons of the 

 ft>rm and frequency of different postures from species to species. It 

 also permits an assessment of the relative amount of agonistic behavior 

 displayed by a given species. The pairing tests allow one to assess 

 the effect of the male on the female throughout pregnancy and parturi- 

 tion. Again one can measure the relative social tolerance. Studies 

 of groups allow one to observe the social tolerance throughout subse- 

 quent generations. 



As discussed under Methods, most of the beha\aoral units described 

 in this section involve an interchange of tactile or visual stimuU. 

 Thus, in this investigation, consideration of presumptive auditory and 

 chemical communication patterns has been minimized. It is under- 

 stood that marking, naso-anal contact, naso-nasal contact, and, to 

 an extent, grooming involve some chemical communication. Although 

 auditory communication was investigated whenever the sounds were 

 l)el()W 15 kc, ultrasonic sounds definitely were excluded in this study. 

 Because of the incomplete nature of tlie sound recordings, a considera- 

 tion of auditory communication will be deferred in this study. 



Aspects of visual communication are difficult to evaluate among 

 nocturnal rodents; however, the striking convergence in color patterns 

 (especially of the tail) between the dipodid genera and the heteromjdd 

 genus Dipodomys deserves special comment. The kangaroo rats and 

 jerboas have relatively large eyes, and in both groups ritualized up- 

 right postures are employed in fighting and durmg initial contact 

 and courtship (see p. 23 and Eisenberg, 1963b). The white tip on 

 the otherwise black terminal tuft of the tail appears to serve as an 

 orientation point for a male when driving a female or when chasing 

 another male. The white ventrum, displayed during a series of up- 

 right postures, produces a sharply contrasting reflecthig surface that 

 surely aids in orientation during sequences of mutual uprights and 

 sparring. This latter characteristic is, however, common to all of 



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