The swallows and swifts are almost constantly on the wing, dexterously catching any insects that come in their way. They are day birds and at night are replaced by the nighthawks that feed upon the night flying insects. Next are the flycatchers that dart “from ambush at passing prey, and with a suggestive click of the bill, return to their post.” The beautiful little hummingbird, ever active on the wing, quickly sees and picks from leaf or flower insects that would escape the attention of other birds. The woodpeckers and allied birds examine the tree trunks and carefully listen for the insect that may be boring through the wood within. The vireos, like the good housekeeper, examine the “nooks and corners to see that no skulker escapes.” The robin and its sister thrushes and the numerous sparrows attend to the surface of the earth, and aquatic birds extensively destroy those insects whose development takes place either in or on the water. Not the least among the birds that assist man in his warfare upon insect pests are our beautiful and active warblers that frequent the foliage of tree and shrubs patiently gathering their insect food. One of these is the Black-throated Green Warbler of our illustration. If we desire to examine its habits, except during the period of migration, we must visit the forests of cone bearing trees in the northern woods of the eastern United States, in the Allegheny mountains and from these points northward to Hudson Bay. It is almost useless to seek this bird in other places. Here, high up in the cedars, pines and hemlock in cozy retreats far out on the branches it builds its nest. “The foundation of the structure is of fine shreds of bark, fine dry twigs of the hemlock, bits of fine grass, weeds and dried rootlets, intermixed with moss and lined with rootlets, fine grass, some feathers and horse hair.” The nests are usually bulky and loosely constructed. These rollicksome Warblers have a peculiar song which is very characteristic and not easily forgotten. The descriptions of this song are almost as numerous as are the observers. One has given this rendering: “Hear me Saint Ther-e-sa.” Another has very aptly described it as sounding like, “Wee-wee-su-see,” the syllables “uttered slowly and well drawn out; that before the last in a lower tone than the two former, and the last syllable noticeably on the upward slide; the whole being a sort of insect tone, altogether peculiar, and by no means unpleasing.” The song of the Black-throated Green Warbler is so unlike that of the other warblers that it becomes an important characteristic of the species. Mr. Chapman says, “There is a quality about it like the droning of bees; it seems to voice the restfulness of a midsummer day.”