Chickadee Revisited

From Birds of Village and Field: A Bird Book for Beginners by Florence Merriam Bailey:

"But though the birds are glad of the dainties we may offer them, they are quite capable of finding food for themselves, even in the bleakest winter weather, for they live on grubs, and on the eggs of moths hidden under the bark of trees. They are particularly fond of the eggs of the canker worm moth. Mr. Forbush of the Massachusetts State Board of Agriculture calculated that one Chickadee in one day would destroy 5,550 eggs, and in the twenty-five days in which the cankerworm moths run or crawl up the trees, 138,750 eggs. He was so impressed with the value of the birds' services that he attracted them to an infested orchard by feeding them there during the winter; and the following summer "it was noticed that while trees in neighboring orchards were seriously infested with cankerworms and to a less degree with tent-caterpillars, those in the orchard which had been frequented by the Chickadees during the winter and spring were not seriously infested, and that comparatively few of the worms and caterpillars were to be found there." Mr. Forbush concludes that birds that eat insect eggs are most valuable to the farmer, as they feed almost entirely on injurious insects and their eggs, and are present all winter when other birds are absent."