ESTIMATING THE STOMACH CONTENTS OF WILD BIRDS 105 



results may be interesting and may have a certain general 

 value, can never afford a basis for anything better than 

 indefinite opinion. It can never settle the case for or against 

 the birds." 



If we state that a certain species of bird has eaten fifty 

 injurious insects and twenty-five beneficial ones, even if 

 the names of the species of insects are mentioned, we learn 

 nothing as to whether the account balances; and if the 

 names of the insects are not mentioned, we are left to guess 

 whether the injurious ones were aphids or cockchafers, and 

 whether the beneficial ones were ichneumon flies or bees. 



Again, if we say that a stomach contained sixty aphids 

 and six bees the idea furnished is a ratio of 60 to 6, but if 

 computed by the percentage of bulk the ratio would be 

 more correctly stated by the figures 3 to 28 of the total food 

 content of the stomach. 



Each bird requires a certain bulk of food per day, not 

 a certain number of different kinds of insects, seeds, etc., 

 and rightly to estimate the importance of any element in its 

 diet we must first know what proportion the insects, seeds, 

 etc., constitute to the standard requirement, and to do so 

 we must express ourselves by some method of measurement. 



If I state in detail, as I have elsewhere, 1 that so many 

 pheasants consume in a year a given number of injurious 

 insects, slugs, earthworms, etc., and so many weed seeds, 

 grains of corn, etc., we may draw the conclusion that their diet 

 is beneficial rather than injurious to the agriculturist ; but we 

 have no exact idea of the degree to which it is beneficial. If, 

 however, I state that 41-7 per cent, of their food consists 

 of leaves, fruits, and seeds of weeds, 2-4 per cent, of grain, 

 and the same percentage of roots and stems, 23-4 of injurious 

 insects, i-o of beneficial insects, 1-5 of neutral insects, 8-7 of 

 earthworms, 2-8 of slugs, and 16-1 of miscellaneous matter, 

 it is possible to interpret these figures. Thus we see that 

 the total animal food consumed is 37-2 and the total vegetable 

 food 62-8. The leaves, seeds, and fruits of weeds, the roots 

 and stems, neutral insects, earthworms, and miscellaneous 

 matter we may regard as neutral, and they constitute 70-4 

 1 Journ. Land Agents' Sec. t 191 3, vol. xii., pp. 583-586. 



77 o 



