2() The Regulative Action of Birds upon Insect Oscillations. 



after subtracting tlie canker-worm ratio from the average of that 

 order taken by the first group, differs by only three per cent, from 

 the average taken by the second group. The discrepancy in the 

 ratios of Coleoptera is not so easily explained, but is distributed 

 among several genera of Scaraba?idje and the small scavenger 

 beetles. The excess of these two orders is compensated princi- 

 pally by diminished ratios of vegetation, which amount to only 

 six per cent, in the birds shot in the orchard, and fifty-two per 

 cent, among those taken through the country at large. Diptera and 

 all the lower orders of insects as well as Arachnida and Myriapoda, 

 are also omitted from the food of the orchard birds. 



Insects composed ninety-seven per cent, of the food of eighteen 

 indigo birds {Passerina cyanea) shot in the orchard, and but fifty- 

 seven per cent, of the food of fifteen individuals taken elsewhere, 

 the balance in both cases being seeds, chiefly Setaria, Polygonum 

 and wheat. The excess of insects in the orchard specimens 

 appears under Lepidoptera and Coleoptera, the former sixty-seven 

 per cent., the latter twenty-nine, as compared with twenty-eight 

 and nineteen per cent, respectively, in the other group. The 

 Lepidoptera of the orchard birds are nearly all canker-worms, as 

 are likewise ten per cent, of those taken by the specimens from 

 various situations. The difference in the ratio of Coleoptera 

 taken by the two groups was exactly compensated by the ten per 

 cent, of Anomala hinotata eaten in the orchard. The excess of 

 caterpillars and beetles taken by the former group, is partly com- 

 pensated also by the almost total disappearance of all other 

 insects from the food. 



What, now, may we conclude, from the above data, respecting 

 the influence of birds upon such entomological insurrections as 

 are illustrated by the uprising of the canker-worms in Mr. Rob- 

 ison's orchard? 



Three facts stand out very clearly as results of these investiga- 

 tions: 1. 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 terrestrial habit, 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 



