CONTENTS 
Page 
Foreword iii 
Origin and Aims of the Study 1 
1. General Background 1 
2. The Experimental Pen 5 
3. The Rats Introduced Into the Pen 8 
4. Objectives of the Investigation 8 
5. Experimental Procedure and the Gathering of Data 9 
6. Acknowledgements 13 
Responses to the Physical Environment 15 
1. Burrow Systems and Harborages 15 
A. The Growth of the Burrow System 15 
B. A Stable Nonsenescing Burrow 20 
C. The Initiation and Expansion of Burrows 21 
D. Orientation of Mounds and Tunnels 24 
a. The Thigmotropic Response to Walls and Other Vertical Barriers Which Extend 
Underground 26 
b. The Deflection or Bifurcation Response in Tunnel Construction 26 
c. Directional Orientation Response Toward Prior Goals 26 
E. The History of a Typical Burrow During its First Few Weeks 27 
F. The Weights of Rocks Moved by the Rats 29 
G. Alteration of Burrows 30 
H. Some Quantitative Aspects of Burrow Systems 42 
I. Pattern of Work as Reflected in Burrow Construction 44 
J. The Location of Chambers 46 
K. The Balance Between Types of Tunnel Segments, and Its Relationship to Social 
Organization 46 
L. Harborage Boxes and Nests 51 
2. Trails, Orientation and the Utilization of Space 54 
A. The Growth of Trails in the Experimental Pen 54 
B. The Position of Trails With Reference to Physical Objects 63 
C. The Wall Response 67 
D. The Movement-Through-Space Hypothesis 70 
E. Orientation in Space 71 
a. Orientation Over Snow 71 
b. Orientation Under Snow 74 
c. Summary of Inferences Concerning Orientation During Formation of Subnivian 
Trails 78 
v 
