BIRDS 127 



lows, swifts, warblers, vireos, flycatchers, tanagers, and the 

 shore birds, woodpeckers, chicadees, and nighthawks are 

 almost entirely insectivorous, and highly beneficial to the 

 farmer, the fruit grower, and the truck gardener. They also 

 protect our flower gardens, our lawns, and our shade trees. 



Even seed-eaters, hke the blackbirds, bobolinks, jays, 

 finches, and sparrows are largely insectivorous; as are also 

 wading birds, grouse, hawks, and owls. The food of nest- 

 hngs, even of seed eaters, is at first composed wholly of soft 

 insects, such as caterpillars, cut-worms, grubs, larvae of ants, 

 etc., flies, plant lice, etc. Gradually harder shelled insects, 

 Hke beetles, bugs, and locusts are added, then berries and 

 fruit, and then hard seeds. Thus even seed-eating sparrows, 

 etc., are valuable as insect exterminators during the breeding 

 season. 



Birds feed especially upon any insects that become un- 

 usually numerous. Thus in plagues of cankerworms, army- 

 worms, or locusts, the birds find this class of food especially 

 abundant, and therefore subsist on it more than ordinarily. 

 In locust years these insects are eaten a great deal even by 

 birds not particularly insectivorous, such as owls, hawks, 

 sparrows, and grouse. Thus, when a plague of insects occurs, 

 the birds' activity in destroying them correspondingly in- 

 creases, and acts as a very great check on their multipli- 

 cation. 



Mr. Forbes made an investigation during a cankerworm 

 plague that was ruining the shade trees, to see how well the 

 birds were doing their work in destroying this pest. He ex- 

 amined the stomachs of 149 birds of 36 different species, 

 and found that 85 birds representing 26 species had eaten 

 the worms. That is, 72 per cent, of the species, and 60 per 



