1. The Social Use of Space 



87 



sufficient generations to permit the evolution of a new species or genus. 

 Stages intermediate between that of constellations and compact colonies 

 may be recognized by the mean interval between adjoining home range 

 centers decreasing from 2 sigma toward zero sigma. 



A. Compact Colony Formation in the Norway Rat 



Over a 27-month period I observed the development of social organiza- 

 tion in a population of Norway rats confined in a one-ciuarter acre enclosure. 

 Preliminary details have already been presented (Calhoun, 1949, 1952), 



Table X 

 Characteristics of Norway Rat Colonies 



and furthei- details will shortly be published (Calhoun, 1963). By the end 

 of the study the population had increased essentially from a single repro- 

 ducing female to 120 adults. These formed 11 clear-cut local colonies 

 (Table X). Each colony inhabited a single burrow or group of neighboring 

 boxes, placed below the surface, to which the rats had access by a drain 

 tile from the surface. Each such burrow or cluster of inhabited boxes was 

 separated from adjacent ones by an average distance of about 35 feet. 

 These are rank-ordered from a to k in a descending order of social rank. 

 For the present purposes we may equate social rank with sex ratio and 

 reproductive success. High-ranking colonies had few males and many 

 females, most of whom successfully reared litters or were pregnant at the 

 time of terminating the study. As social rank of the colony decreased there 



