BIRDS AS REGULATORS OF OUTBREAKS. 73 



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. 



u (2) The comparisons made show plainly that the reflex 

 effect of this concentration on two or three unusually nu- 

 merous insects was so Avidely distributed over the ordinary 

 elements of their food that no especial chance was given for 

 the rise of new fluctuations among the species commonly 

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

 canker-worm and the vine-chafer was compensated by a gen- 

 eral 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 w^ere compared with 

 those made elsewhere 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 caterpil- 

 lars, goes to show that these insects are favorites with a 

 majority of birds.' 1 



One of the most notable series of studies of the relation 

 of birds to outbreaks of injurious insects was that carried on 

 for thirteen years by Professor Samuel Aughey, of the Uni- 

 versity of Nebraska, concerning the extent to which birds 

 feed upon the Rocky Mountain locust or grasshopper during 

 the periodic outbreaks of that insect. Fortunately, the results 

 of these studies have been preserved by the United States 

 Entomological Commission. 1 Between 1865 and 1877 Pro- 



1 First Report, Appendix II. 



