450 McAtee, Contents of Bird Stomachs. [q^ 



be examined. Later he states that conclusions must not be drawn 

 from a small number of records, we must take a fair average. These 

 things are exactly what every economic investigation, worthy of 

 the name, strives to do, and what has been done with great success 

 in the case of numerous species of birds in the United States. The 

 final percentages of food obtained for some species are not changed 

 by 1 per cent, by the addition of 100 stomachs taken in a restricted 

 area in a single season. 



The numerical system (which Mason prefers) of denoting the 

 contents of bird stomachs in contrast to the percentage-by-volume 

 system, has assumed a number of different forms. The modifica- 

 tions we are acquainted with are as follows : 



1. Gives total numbers of various groups of insects, seeds, etc., 

 taken by the whole collection of birds examined. 



2. States the total number of birds, taking certain items of 

 food, or in other words, the number of times a certain food is taken. 



3. States the number of birds eating certain articles of food and 

 the number of specimens taken. 



4. The proportion of the number of times a certain food is 

 taken to the total number of times all foods are taken, is considered 

 the percentage of that food in the diet. 



5. Estimates the proportions of food items according to their 

 numerical representation among the total of all specimens eaten. 



No. 1 is used by Mason (1. c), No. 2 by Fisher.^ No. 3 by King ^ 

 and Newstead,^ No. 4 by Gilmour,^ and No. 5, for the estimation 

 of animal food only, by Wilcox.^ The last named estimates the 

 percentages of vegetable food by bulk. 



Thus 6 investigators who have tried to present the results of 

 stomach examinations by a numerical system, have adopted at 

 least 5 very distinct methods. This indicates that no very satis- 

 factory numerical system has thus far been proposed, a fact which 

 has not however prevented 3 of these men, viz : Mason, King, and 

 Wilcox, from severely criticising the percentage-by-volume method. 



1 [Fisher, A. K.] Bui. 1, Biol. Survey, 1889, pp. 133-143, and Bui. 3, Biol. Survey, 

 1893. 



2 King, F. H. Trans. Wis. State Agr. Soc, Vol. XXIV. 1S86. 



» Newstead, R. Suppl. Joiirn. Bd. Agr. [London], XV, No. 9, Dec., 1908. 

 < Gilmour, John. Trans. Highland and Agr. Soc. Scotland, 1896, pp. 1-93. 

 » Wilcox, E. V. Bui. 43, Ohio Agr. Exp. Sta., Sept., 1892, pp. 115-131. 



