2. Total length (tip of nose to tip of tail), and 
tail length in mm. 
3. Sexual condition: 
a. For males: Whether or not the testes were 
descended into the scrotum. 
b. For females: 
Whether or not the vagina was per- 
forated; 
Whether or not embryos could be pal- 
pated; 
The condition of the nipples. 
4. The size and number of wounds. 
5. The character of the pelage. 
6. Date and location of capture. 
Observations from the tower were kept chrono- 
logically. The contained data were transferred 
at a later date to cards (fig. 12) so that every ob- 
servation pertaining to each individual rat was 
filed chronologically under its eartag number. 
The front of each card contained a list of some of 
the possible topics which might designate the be- 
haviors described on the reverse side of the card. 
By placing checks in the appropriate places, later 
sorting of the data was facilitated. 
At fairly regular intervals detailed surveys of the 
pen were made on enlarged field maps to show the 
locations of all changes in the environment made 
by the rats. In addition, the surfaces of the burrows 
were mapped in even greater detail. Particularly 
detailed maps were always prepared of trails fol- 
lowing snowfalls, since these presented good records 
of orientation responses. A photographic record 
was made of all pertinent alterations to the en- 
vironment produced by the rats. 
6 . Acknowledgments 
This study was made possible by a grant from 
the International Health Division of the Rocke- 
feller Foundation to the School of Hygiene and 
Public Health of the Johns Hopkins University 
for the founding of the Rodent Ecology Project. 
This project was placed in the general supervision 
of the Department of Parasitology, which was 
headed by Dr. W. W. Cort. 
I am in great debt to the extensive knowledge of 
the biology of the wild Norway rat and the tech- 
niques of study established by Dr. Curt P. Richter, 
Dr. John T. Emlen, Jr., Mr. Allen W. Stokes, and 
Dr. David E. Davis before my arrival at Johns 
Hopkins. W ithout that as a basis it would have 
been impossible to conceive of the present problem 
and to proceed with its analysis. Once the prob- 
Ear Tag 
Date (Handled) 
Age in days 
Weight in grams 
Body in mm. 
Tail in mm. 
Wounds 
Body/Tail 
Weight/Body 
Growth Index 
Card number 
Sex 
Date born 
Litter Number 
Mother 
Birthplace 
Place today 
Sexual condition 
Pelage condition 
Behavior Notes Recorded On Reverse Side 
: Competitive 
: Play fighting 
: Psychol, drubbing 
: Nose touching 
: Sparring-tumbling 
: Chase 
: Territorial 
: Vocalization 
: Manual abiliity 
: Orientation 
: Nest building 
: Burrow building 
: Aggregations 
Food storage 
Food acquisition 
Water 
Elimination 
Sexual behavior 
Rolling 
Following 
Copulation 
Homosexual 
Mother-young 
Among young 
Adults-young 
Inter-adult 
Figure 12. — Sample of 5- by 8-inch card onto which all 
data was either recorded or later transferred. Details of 
the observation were recorded on the back of the card. 
lem was decided upon, its prosecution was greatly 
enhanced by the freedom permitted me by Dr. 
David E. Davis, who was directing the general 
program of the Rodent Ecology Project during 
these years. 
Once the problem of investigating a free-ranging 
population of rats under semicontrolled conditions 
was conceived, it then became necessary to secure 
a suitable location for the establishment of the 
colony. During my association with the Johns 
Hopkins University I lived at the edge of a small 
suburban community north of Towson, the county 
seat of Baltimore County, Md. Surrounding this 
community there were several hundred acres of 
semiforest and forested land. That portion im- 
mediately adjoining my residence was owned by 
the late Mr. John O’Donovan of Dulaney Valley 
Road. He granted permission for the establish- 
ment of the experimental setup in a partial clearing 
13 
