18 The Regulative Action of Birds upon Insect Oscillations. 
food, and the eggs to the small species which pry about the trunks 
of trees. The entire period during which the insect is doubtless 
fed upon by birds will usually amount to somewhat more than 
two months. 
Besides the abundance of the canker-worms noted in the food 
of these birds, it is evident that two or three other species of insects 
occurred in this situation in extraordinary numbers, especially the 
vine leaf-chafer ( Anomala binotata) and a small borer ( Psenocerus 
supernotatus). The purple cut-worm ( Nephelodes violans) was 
also somewhat commoner than usual. The Anomala was eaten 
by thirty-nine of the specimens, representing fifteen species, and 
amounted to eleven per cent, of the food of all the birds taken in 
the orchard. Many of these were too small to feed upon so large 
an insect, and a better illustration of the abundance of this 
beetle may be gathered from the food of the thrushes and blue- 
bird. Of thirty-two specimens of these families, nineteen had 
eaten the vine leaf-chafer, which amounted to twenty-seven per 
cent, of the food of all. Only fourteen of the same birds had 
eaten the canker-worm, which amounted to less than twenty per 
cent, of the food. It seems likely, therefore, that some of these 
birds were attracted to the orchard, not by the canker-worms, but 
by the superabundance of Anomala. The unusual frequency of 
Pseyioeerus supernotatus , a small long-horned beetle found upon 
the trees, is shown by the fact that of the twenty-five small arboreal 
birds (Paridae, Troglodytidas, and Mniotiltidae), thirteen had eaten 
this beetle, which composed nearly one-tenth of their food. 
We have next to make the comparison of the food 
taken in the orchard by the species most abundant there, 
with the food of the same species, taken elsewhere under 
ordinary circumstances. For the purpose of this compar- 
ison I have selected the robin, the catbird, the black-throated 
bunting ( Spiza americana) , and the indigo bird ( Passerina 
cyanea'). In the table of the ordinary food of the robin for 
May, published in Bulletin 3 of this series, as represented by 
fourteen specimens, caterpillars amounted to but twenty-three per 
cent., whereas in the orchard they rise to fifty-four per cent. This 
difference between the averages is almost exactly accounted for 
by the ratios of canker-worms and Nephelodes violans not appear- 
ing on the former table; these together amounting to thirty-five 
