454 McAtee, Contents of Bird Stomachs. [q^^ 



greatly or only moderately beneficial or injurious? do the figures 

 give us any idea as to whether this account about balances? or 

 whether one side greatly overbalances the other? 



On the contrary it is evident that they stand just as much in 

 need of interpretation, as do percentages. Hence the question 

 between the two systems is not purely one of expression of economic 

 values, as some supporters of the numerical system would have 

 us believe, but one of the means best adapted to expressing the rela- 

 tions between the various food elements. To the writer's mind 

 the percentage-by-bulk system has all the better of the argument, 

 but let us not so decide without giving the various numerical 

 systems a hearing. 



Mason says, "What we want to know is the exact number of 

 grains of corn, the number of insects, etc." To illustrate we may 

 cite one of Mason's summaries: "Of 142 insects taken by 12 birds, 

 7 are beneficial, 50 injurious and 85 neutral." (p. 118.) Are we 

 to understand that this bird does good and harm in the proportions 

 of 50 to 7? Not unless the insects mentioned are of equal size or 

 at least of equal capacity for good or harm.^ Suppose the useful 

 species are large forms which do a great deal of good, and the 

 injurious ones small ones of no consequence. Or if you please, 

 make just the reverse supposition. In neither case do the figures 

 above supply the information necessary to reach a final conclusion. 

 The objection that these authors make to our percentages, apply 

 equally well to their figures — they do not give any idea as to the 

 true economic ratios. Like the percentages they must be inter- 

 preted. 



The principal variation of the numerical system aside from that 

 of Wilcox, which has previously been discussed, is that used by 

 John Gilmour in his paper ^ on the Wood Pigeon, Rook and Starling. 

 In a review of this paper Professor Beal states:^ "Mr. Gilmour 

 reckons his percentages from the number of times that the bird 

 has taken the food, and from this concludes that grain and husks 

 constitute 58 per cent of the Rook's food. Insects and grubs 



' Insects whose economic status depends upon their food habits, and this in- 

 cludes the majority, are very properly reckoned by bulk, for as a rule the larger 

 will do more harm or good than the smaller ones. 



2 Trans. Highland and Agr. Soc. Scotland, 1896, 1-9.3. 



5 Auk XrV. No. 1, Jan., 1897, p. 10. 



