ESTIMATING THE STOMACH CONTENTS OF WILD BIRDS 103 



ON THE VALUE OF THE DIFFERENT METHODS 

 OF ESTIMATING THE STOMACH CONTENTS 

 OF WILD BIRDS. 



By Walter E. Collinge, D.Sc, F.L.S., Carnegie Fellow, and 

 Research Fellow of the University of St Andrews. 



As the study of Economic Ornithology becomes more 

 intensive, we are led to examine more critically than hereto- 

 fore the results obtained by different workers, and in doing 

 so we are forced to the conclusion that the methods employed 

 are not always the best, and in consequence much of the 

 value of their work is lost. 



It is obvious that any method that is capable of more 

 than one interpretation is of little value, as compared with 

 one that expresses accurately the ratios each food element 

 bears to the others. Lord Kelvin has said : " When you 

 can measure what you are speaking about, and express 

 it in numbers, you know something about it ; but when 

 you cannot measure it, when you cannot express it in 

 numbers, your knowledge is of a meagre and unsatisfactory 

 kind ; it may be the beginning of knowledge, but you have 

 scarcely in your thoughts advanced to the stage of science." 



This is very largely what has been taking place in this 

 country as regards estimating the food found in the stomach 

 and crop of different wild birds. We have failed to measure 

 the quantities of the different kinds of food, simply expressing 

 the number of weed seeds, injurious insects, grains of wheat, 

 etc. That a better and more scientific method exists, I 

 shall attempt to show in this paper. 



Three methods have been used in estimating the amount 

 of food in a bird's stomach, viz., the different articles may 

 be counted == the numerical method ; they may be weighed 

 = the gravimetric method ; or they may be estimated accord- 

 ing to their volume = the volumetric method. 



This last method is the one adopted since 1895 by the 

 Biological Survey of the U.S. Department of Agriculture, 

 from which department more work has emanated than from 



