226 ENTOMOLOGY 



To quote Forbes: "Three facts stand out very clearly as results of 

 these investigations: i. Birds of the most varied character and habits, 

 migrant and resident, of all sizes, from the tiny wren to the blue-jay, birds 

 of the forest, garden and meadow, those of arboreal and those of terres- 

 trial habits, were certainly either attracted or detained here by the 

 bountiful supply of insect food, and were feeding freely upon the species 

 most abundant. That thirty-five per cent, of the food of all the birds 

 congregated in this orchard should have consisted of a single species of 

 insect, is a fact so extraordinary that its meaning can not be mistaken. 

 Whatever power the birds of this vicinity possessed as checks upon 

 destructive irruptions of insect life was being largely exerted here to 

 restore the broken balance of organic nature. And while looking for 

 their influence over one insect outbreak we stumbled upon at least two 

 others, less marked, perhaps incipient, but evident enough to express 

 themselves clearly in the changed food ratios of the birds. 



"2. The comparisons made show plainly that the reflex effect of this 

 concentration on two or three unusually numerous insects was so widely 

 distributed over -the ordinary elements of their food that no especial 

 chance was given for the rise of new fluctuations among the species com- 

 monly eaten. That is to say, the abnormal pressure put upon the canker- 

 worm and vine-chafer was compensated by a general diminution of the 

 ratios of all the other elements, and not by a neglect of one or two alone. 

 If the latter had been the case, the criticism might easily have been made 

 that the birds, in helping to reduce one oscillation, were setting others on 

 foot. 



"3. The fact that, with the exception of the indigo bird, the species 

 whose records in the orchard were compared with those made -else where 

 had eaten in the former situation as many caterpillars other than canker- 

 worms as usual, simply adding their canker-worm ratios to those of other 

 caterpillars, goes to show that these insects are favorites with a majority 

 of birds." 



The Relations of Birds to Predaceous and Parasitic Insects. 

 The false assumption is often made that a bird is necessarily inimical to 

 man's interest whenever it destroys a parasitic or a predaceous insect. 

 Weed and Dearborn attack this assumption as follows: 



"Suppose an ichneumon parasite is found in the stomach of a robin 

 or other bird: it may belong to any one of the following categories: 



4 1. The primary parasite of an injurious insect. 



"2. The secondary parasite of an injurious insect. 



"3. The primary parasite of an insect feeding on a noxious plant. 



