110 The Food of Birds. 



iiiary of the food of the robin as a species in at least the 

 northern half of the state, and under the ordinary condi- 

 tions of the last five or six years. Of course, I had no idea 

 how these averages were coming out until my notes were 

 finished and the ratios were calculated for the whole. 



Economic Relations. 



We come now to the intricate, delicate and difficult 

 question of the economic relations of this species ; — a 

 question rendered less important by the general considera- 

 tions urged elsewhere, but, nevertheless, deserving careful 

 attention. While it is true that every insectivorous bird 

 must be respected, whatever its other habits, at least un- 

 til we clearly understand its function in the general order 

 and are certain that its removal will do no harm which we 

 can not remedy or endure better than we can support its 

 injuries, yet an idea of the relative importance of edible 

 fruits and insects of both the beneficial and injurious classes 

 in the diet of the bird is necessary as a step to this clear 

 and complete understanding of the matter. 



Glancing at the bottom of the table of the food of the 

 species, on page 115, the reader will see three lines of fig- 

 ures running across the page, showing for each month the 

 percentages of beneficial, injurious and neutral species of 

 insects and fruits eaten by these birds. The figures at the 

 right give similar percentages for all the birds for the entire 

 year. Following the upper line, we note the small percent- 

 ages of injury done in the early spring, the marked increase 

 of injury in April, due to the excessive destruction of pre- 

 daceous beetles, and the heavy percentages of the fruiting 

 months. The general average of beneficial elements des- 

 troyed for the year is thirty-six per cent. On the second 

 line we notice an inverse variation. Commencing with a 

 ratio of ninety-four per cent, of injurious elements eaten 

 in February (if we include the larva of Bibio in these), 

 the record runs down to seven per cent, in September, the 

 general average for the year being forty-three per cent. 



This comparison, however, is merely a quantitative one. 

 Injurious or beneficial elements are balanced against each 

 other according to their bulk and not their quality. A 



