The Regulative Action of Birds upon Insect Oscillations. 21 
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 evi- 
dent 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 commonly eaten. That is to say, the abnormal 
pressure put upon the canker-worm and vine chafer was compen- 
sated by a general diminution of the ratios of all the other ele- 
ments, 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 elsewhere, had eaten in the former situation as many cater- 
pillars 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. 
