NO. 3597 RODENT ETHOLOGY — EISENBERG 25 



At the time of ejaculation, the genus Perognathus exhibits a 

 singular pattern. The male P. calijornicus rolls to one side while, in 

 the case of P. inornatus and P. parvus, the female generally twists over 

 on her side, frequently throwing the male over also. 



This brief review should indicate that considerable uniformity in 

 sexual behavior exists when species of the same genus are compared 

 (e.g., Perognathus and Dipodom.ys). Table 18 summarizes the unique 

 featm^es of several rodent copulation patterns. Reference to this 

 table further indicates that considerable variability can exist among 

 the genera of a single family. At this time the adaptive significance of 

 such differences is not apparent although one can surmise that Di- 

 poflomys, which exhibits such a sustained mount, sm'ely must copulate 

 underground in burrows. 



Pair tolerance.- — The data for this section were obtained by 

 allowing a male to remain with a female throughout the parturition 

 and rearing of the litter. Mere tolerance without fighting by a pan- 

 in the absence of reproduction was not accepted as evidence for social 

 tolerance (see p. 3). Since the tolerance is in part a function of 

 space, the dimensions of the cage are listed for all experiments. 

 Further, the species ranged in size from 12 grams to 150 grams adult 

 weight. To correct for this size bias, I have listed for each cage size 

 two correction factors that express the area in terms of square inches 

 per gram of animal and square inches per animal. 



In general, even females of the most tolerant species will withdi'aw 

 and nest separately at the time of partiu"ition ; however, tolerant 

 species show a compatibility that permits sustained contact without 

 extreme aggression throughout the fii'st few hours after parturition 

 and on through the rearing phase. Table 19 summarizes the pairing 

 tendencies for several species prior to and through the female's 

 estrous period. Those that exhibited solitary nesting tendencies 

 were not paired beyond the mating; the more tolerant species were left 

 together through parturition. This second class of data is summarized 

 in table 20. Table 21 summarizes the data for those species that did 

 not breed for various known and unknown reasons. The conclusions 

 are as follows : 



Regardless of the animal's size, given at least 70 to 90 square 

 inches per animal, the normally tolerant species will conceive and 

 remain compatible throughout partm'ition. The more intolerant 

 species require greater space in order to avoid contact. One can 

 breed the less tolerant species either by providing them with a larger 

 space or by utiUzing a series of staged encounters through a female's 

 estrous period followed by total separation through the parturition 

 and rearing phases (Eisenberg and Isaac, 1963). 



