DESTRUCTION OF INSECTS BY BIRDS.

Forest and Bird, Issue 28, 1 October 1932, Page 11

DESTRUCTION OF INSECTS BY BIRDS.

An examination of numerous bird stomachs has shown that the larger proportion of insects taken is made up of vegetableeaters. This is not surprising when we stop to consider that the vegetable-eaters far outnumber the other forms in nature. Both are destroyed in proportion to their numbers. It so happens that, as in the case of the cabbage-caterpillar, the vegetable-eater is not destroyed by parasites until great damage to crops has been accomplished. The second generation, it is true, is reduced in numbers, but not before the first generation has inflicted serious loss upon the farmer. Birds, therefore, by consuming the caterpillar, though with it a number of parasitical larvae may be destroyed, are saving the farmer from a direct money loss. As a matter of fact the agriculturalist is more indebted to birds for the preservation of his growing crops than to any other living creatures. In the predatory insects he finds true helpmates who destroy much of the smaller fry; but the rapacious caterpillars, cicadas, and grasshoppers are too large for them to attack. Parasites deal with these forms, but their action is slow and affects the immediate crop little. A few years ago the United States Department of Agriculture set aside a tract of land in Maryland with the view of determin-

ing the exact status of birds on a farm. It was necessary, in order to get at their stomach contents, to shoot a great number of individuals. In all, 645 birds were killed during the experiment. The results proved interesting. Virtually all the birds, at one time of year or other, included insects as a part of their menu. Twenty-four species fed on grasshoppers, twenty-one took leafmining beetles, thirty-nine consumed ants, and forty-four had eaten weevils. Most birds took two, three, or all the forms of insects mentioned. About one-third of all the food consumed by the 645 consisted of insects, 27 per cent, of which were harmful to crops and less than 4 per cent, were beneficial. These were the average birds—robins, catbirds, swallows, woodpeckers, kingbirds, crows and the like —that are found on any typical farm of the eastern United States. —'“The Importance of Bird Life.”