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 (Ationiala hinotata) and a small borer (^Psenocerus 

 supernotatus). The purple cut-worm {Neplielodes 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 

 Psenocertis Hupernotatus., a small long-horned beetle found upon 

 the trees, is shown by the fact that of the twenty-five small arboreal 

 birds (Paridfe, Troglodytidaj, and Mniotiltid;\^), 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 {Spizci americana), and the indigo bird {Passerhia 

 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 Neplielodes violans not appear- 

 ing on the former table; these together amounting to thirty-five 



