The Regulative Action of Birds upon Insect Oscillatvmn. 19 



per cent. Notwithstanding the number of Anoniala eaten in the 

 orchard, the ratios of the Scarabanda* are substantially the same, 

 as the ordinary food of the robin in May consists largely of June 

 beetles. The surplus of Lepidoptera seems to be balanced by a 

 deficiency in all the other orders, no one of which rises to the 

 average of its ordinary food in May. The loss is greatest, how- 

 ever, in the Diptera, which drop from eleven per cent, to nothing. 



Comparing the record of the fourteen catbirds shot in the 

 orchard with that of twenty-two obtained in miscellaneous situa- 

 tions, we note, first, that the caterpillars on the first table are 

 more than twice those of the second, — twenty-six in the one, and 

 twelve in tlie other; and that this difference is evidently due to 

 the fifteen per cent, of canker-worms taken by the birds of the 

 first group. This shows that the catbird, like the robin, had 

 simply added tiie canker-worms eaten to its usual ratio of cater- 

 pillars. A more striking difference is shown in the totals of 

 Coleoptera, wliich stand at fifty-six per cent, in the orchard birds, 

 and twenty-three in the others. This, again, is evidently due to 

 the abundance of A/iumala hinotata; for when the ratio of this 

 insect is subtracted from the total of Coleoptera, the remainder is 

 twenty per cent, as against twenty-three of the ordinary food. 

 These excessive ratios of Lepidoptera and Coleoptera are com- 

 pensated by deficiencies in the Diptera, Arachnida, Myriapoda 

 and Ortlioptera, especially in the three first named groups. The 

 decided preference of this bird for ants is shown by the fact that 

 the usual ratio of these insects is scarcely diminished, fourteen 

 per cent, having been taken in the orchard and eighteen else- 

 where. 



Fourteen of the black-throated bunting {^Spiza americana)^ 

 killed in the orchard, are to be contrasted with twelve shot in 

 May from various situations. A striking difference is seen at 

 once in the insect ratios, which amount respectively to eighty- 

 eight and forty-seven per cent. This surplus of insects eaten by 

 the orchard birds is readily traced to the orders Lepidoptera and 

 Coleoptera. Of the former these birds had eaten more than three 

 times their ordinary average, and of the latter nearly four times 

 the usual amount. The excess of Lepidoptera is clearly due, as 

 usual, to the presence of the canker-worms, since the balance left 

 3 



