FOREWORD 
This study describes the way of life of the Norway 
rat observed over a 27 month period in a quarter- 
acre enclosure in which environmental conditions 
simulated those characterizing this species in its 
native haunts. Typically, this species lives in 
close relationship with man (4, 5, 25, 26, 28, 29, 
31, 67, 88). The present report comprises a small 
segment of a broader program of investigation 
into the biology of this species and its relationship 
to man contributed to by a number of workers 
at the Johns Hopkins University (e.g., 3, 4, 5, 6, 
8, 9, 22, 23, 25, 26, 28, 34, 35, 66, 68, 84, 88). Among 
these investigators, I am particularly indebted to 
Drs. Curt P. Richter, John T. Emlen, Jr., David 
E. Davis, and Allen W. Stokes. Had it not been 
for the insights and techniques developed by 
them, the formulation and conduct of the present 
study would have been much less effective. 
Their studies were conducted in various habitats, 
such as on farms, or surrounding human habi- 
tations where Norway rats normally occur. Under 
these circumstances rats may be trapped, marked, 
and recaptured, but normally great difficulty is 
experienced in following the history of any par- 
ticular individual throughout its life. It is even 
more difficult to observe the behavioral relation- 
ships among known individuals in most situations 
where rats maintain a commensal relationship 
to man. In order to circumvent this difficulty I 
established a few rats in a quarter- acre enclosure. 
From a single successfully reproducing female there 
developed a total population of over 200 individuals 
spanning four generations during the 27 months of 
study. 
Every rat was trapped and handled on many 
occasions. In addition every individual was 
marked by removing small spots of fur with a 
depilatory. This marking enabled observation of 
the behavior of the rats from a tower constructed 
outside the enclosure. Such observation permitted 
the accumulation of a large body of information 
regarding relationships among the members of 
the enclosed population. At the termination of 
this study I decided that its value lay in a detailed 
examination of all these relationships. This 
proved a more difficult and time consuming task 
than anticipated. During the next few years, 
following the termination of the study by June 
1949, my superiors at three institutions provided 
me with the opportunity and facilities for making 
the necessary detailed analyses reported here. 
In this connection I am greatly indebted to the 
following persons and institutions: 
1. Dr. J. P. Scott and the Roscoe B. Jackson 
Memorial Laboratory, Bar Harbor, Maine. 
2. Dr. David McK. Rioch and the Walter Reed 
Army Institute of Research, Washington, D.C. 
3. Dr. David Shakow and the National Institute 
of Mental Health, Bethesda, Md. 
My objective in this report has simply been to 
describe the results derived from the 27 months’ 
observation of this enclosed population. Al- 
though I have found it useful to coordinate certain 
data reported in the literature with my observa- 
tions, no attempt has been made to evaluate all 
literature relevant . to the ecology and sociology 
of the Norway rat. I have viewed this study as 
an opportunity to seek useful concepts, whose 
validation certainly requires further investigation. 
To this end I have frequently searched for impli- 
cations beyond those definitely substantiated by 
the recorded observations. During the years since 
completion of this study I followed up some 
of the leads suggested by it (16, 91, 100, 101, 102). 
John B. Calhoun, 
Laboratory of Psychology, 
National Institute of Mental Health, 
Bethesda, Md. 20014 
December 6, 1962. 
