The book has been written entirely by Gabrielson, but a large part of 

 the endless task of checking records and literature has been assumed by 

 Jewett. For the identifications and for distribution data, the authors are 

 jointly responsible, except that in some of the more difficult groups the 

 specimens have been submitted to others. To these men, especially to Dr. 

 H. C. Oberholser, Dr. Joseph Grinnell, Harry S. Swarth, and George 

 Willett, the authors are particularly grateful for their patience in helping 

 with knotty problems and answering inquiries. 



It would be grossly unfair not to acknowledge the constant encourage- 

 ment that has been received from Dr. A. K. Fisher, Dr. W. B. Bell, and 

 Stanley P. Young, under whose direction the authors have at various 

 times been engaged in rodent and predatory animal control work. Recog- 

 nizing the importance of the research work necessary, Mr. Young not 

 only allowed ample time to work out special problems and to prepare this 

 book, but also furnished clerical help when it could be spared from 

 regular duties. 



To the State College Committee in charge of the publication of the 

 Oregon State Monographs, a research series in which this study has been 

 assigned a place, grateful acknowledgment is extended for their efficient 

 service in arranging for the publication of the book and for valuable 

 editorial assistance. 



The work has thus become a joint enterprise of the Bureau of Biological 

 Survey and the Oregon State College, the College having handled the 

 publication of the report. 



IRA N. GABRIELSON, 



Chief, Bureau of Biological Survey. 



