PERCENTAGES OF ANIMAL AND VEGETABLE FOOD. 



29 



or other animals has been recorded also, but these numbers have not 

 been considered in determining percentages. 



RELATIVE PERCENTAGES OF ANIMAL AND VEGETABLE FOOD. 



The average quantities of animal, vegetable, and mineral matter 

 contained in the entire number of stomachs could be easily computed; 

 but such averages would be of little value in view of the wide differ- 

 ences in the numbers of stomachs examined in different months. Evi- 

 dently the averages for the year must be obtained on a different basis, 

 allowance being made for the discrepancies in the number of stomachs 

 examined. The nearest approach to such a basis is found in the 

 monthly averages given in the following table : 



Table showing average percentages of the animal, vegetable, and mineral contents of 909 

 Crow stomachs, arranged by months. 



Month. 



January . . 

 February . 

 March 



April 



May 



June 



July 



August — 

 September. 

 October. . . 

 Sovember 

 December. 



Number 

 examined. 



Animal. 



Vegetable. 



53 



21.5 



60.9 



23 



10 



71 



26 



19.2 



67 



42 



62.1 



31. 2 ! 



364 



66.6 



29.5 



165 



49.5 



46.3 



45 



37.3 



55. 6 



24 



37 



56.9 I 



44 



27.1 



66 



46 



18.8 



67.4 



18 



33.2 



55.5 ! 



59 



12.1 



74.3 { 



17.6 

 19 



13.8 

 6.7 

 3.9 

 4.2 

 7.1 

 6.1 

 6.9 

 13.8 

 11.3 

 13.6 



By averaging these results it is possible to reach a conclusion which 

 is correct so far as the monthly averages themselves are trustworthy. 

 In cases where 40 or more stomachs have been averaged for any one 

 month the result may be taken as approximately correct, and when, as 

 in May and June, the number exceeds 100, it is probable that the 

 examination of twice as many would not alter the averages materially, 

 ^November is the month about which most doubt exists, although the 

 numbers for February and March are also too small. The results in 

 the case of the last-mentioned months, however, are strengthened by 

 the examination of material from the crow roosts, while the results 

 for August are partially confirmed by the fact that they are, as theo- 

 retically they should be, intermediate between those of July and 

 September. 



On this basis the annual averages of stomach contents are as follows : 

 Animal matter, 32.9 percent; vegetable matter, 56.8 percent, and 

 mineral matter, 10.3 percent. Eoughly speaking, it may be said that 

 one-third of the food annually consumed by Grows consists of animal 

 matter, about three-fifths of vegetable matter, and about one-tenth of 

 mineral matter. Of course the latter component is not food, strictly 

 speaking, and its elimination would change the proportions of food 

 proper to: Animal food, 36.6 percent; vegetable food, 63.4 percent 



