20 



INTRODUCTION 



to this definite end that the work here undertaken has been ad- 

 dressed. 



It was some twenty-five years ago that the writer made the first 

 examinations of the stomach contents of raptorial birds upon which 

 this work is based. The appearance in 1903 of Dr. A. K. Fisher's 

 Hawks and Owls of the United States, to which continual reference 

 is herein made, was a very definite stimulus in the keeping of field 

 records, and in the less agreeable though more informing task of 

 examining the stomachs. During succeeding years, as opportunity 

 offered, both dissections and field observations have been made. 

 Birds of prey as a rule are not easily studied in the field, because of 



Fig. 2. The level Kansan drift plain of northeastern O'Brien county (Loos). 



their naturally shy or distrustful dispositions. Of the individuals 

 killed relatively few reached the hands of an ornithologist. In con- 

 sequence the data obtained during a single season or within a year 

 are insufficient as a basis for generalizations concerning a species, 

 a series of years being required for the collection of adequate data. 

 Furthermore, the existing collections of skins of the raptorial birds 

 to be found in even the leading American museums are sadly de- 

 ficient in data relative to the stomach contents of the birds at the 

 time of preparation, only an occasional bit of information being 

 available from these sources. 



