through the lungs into hollow spaces filled with air, which are found between the organs of the body. The high temperature of the bird is a direct result of this rapid oxidation and also because the feathers and the oily skin form an insulation which does not readily permit of the escape of heat. This fact is of much use to the bird in its flights at great altitudes, where the temperature is often very low. The Nervous System and the Senses. — The central nervous system is well developed. A large forebrain is found, which, according to a series of elaborate experiments with pigeons, is found to have to do with the conscious life of the bird. The cerebellum takes care of the acts which are purely mechanical and are concerned with the living (digestion, absorption, beating of the heart, etc.) of the bird. Sight is probably the best developed of the senses of a bird. The keenness of vision of a hawk is proverbial. It has been noticed that in a bird which hunts its prey at night, the eyes look toward the front of the face. In a bird which is hunted, as in the dove, the eyes are placed at the side of the head. In the case of the woodcock, which feeds at night in the marshes, and which is in constant danger from attack by owls, the eyes have come to lie far back on the top of the head. Hearing is also well developed in most birds; this fact may be demonstrated with any canary. The sense of smell does not appear to be well developed in any bird, and is especially deficient in seed-eating birds. Nesting Habits. Among the most interesting of all instincts shown by birds are the habits of nest building. We have found that some invertebrates, as spiders and ants, protect the eggs when laid. In the vertebrate Hence a nest, in which to rest, is needed. The ostrich is an exception; it makes no nest but the male and the female take turns in sitting on the eggs. Such birds as are immune from the attack of enemies, either because of their isolation, or their protective Nest of the chimney swift. coloration (as the puffins, gulls, and terns), build a rough nest among the rocks or on the beach. The eggs, especially those of the tern, are marked and colored so as to be almost indistinguishable from the rocks or sand on which they rest. Other birds have made the nest a home and a place of refuge as well as a place to hatch the eggs. Such is the nest of the woodpecker in the hollow tree and the hanging nest of the oriole. Some nests which might be easily seen because of their location are often rendered inconspicuous by the builders; for example, the lichen-covered nest of the humming birds. Care of the Young. After the eggs have been hatched the young in most cases are quite dependent upon the parents for food. Most young birds are prodigious eaters; as a result they grow very rapidly. It has been estimated that a young robin eats two or three times its own weight in worms every day. Many other young birds, especially kingbirds, are rapacious insect eaters. In the case of the pigeons and some other birds, food is swallowed by the mother, partially digested in the crop, and then regurgitated into the mouths of the young nestlings. Food of Birds. The food of birds makes them of the greatest economic importance to our country. This is because of the relation of insects to agriculture. A large part of the diet of most of our native birds includes insects harmful to vegetation. Investigations undertaken by the U.S. Department of Agriculture (Division of Biological Survey) show that a surprisingly large number Spiders May Beetles Caterpillars Etc. CUCKOO Ants Cut Worms Stink Bugs Stink Bugs Wevils HOUSE WREN BANK SWALLOW Beetles Spiders Etc. Insects Bugs Etc. of birds once believed to harm crops really perform a service to the farmer by killing injurious insects. Even the much maligned crow lives to a large extent upon insects. During the entire year, the crow eats about 25 per cent insect food and 29 per cent grain. In May, when the grain is sprouting, the crow is a pest, but he makes up for it during the remainder of the summer by eating harmful insects. The robin, whose presence in the cherry tree we resent, during the rest of the summer does untold good by feeding upon noxious insects. Birds, as a rule, feed upon the substances which are most abundant around them at the time. The following quotation from I. P. Trimble, A Treatise on the Insect Enemies of Fruit and Shade Trees, bears out this statement: "On the fifth of May, 1864, . . different birds. .. had been feeding freely upon small beetles. seven There was a great flight of BARN SWALLOW Beetles GRAIN RED WINGED Beetles FRUIT Beetles Crasshoppers Etc. CORN CROW BLACKBIRD GRAIN beetles that day; the atmosphere was teeming with them. A few days after, the air was filled with Ephemera flies and the same species of birds were then feeding upon them." 1 1 During the outbreak of Rocky Mountain locusts in Nebraska in 1874-1877, Professor Samuel Aughey saw a long-billed marsh wren carry thirty locusts to her young in an hour. At this rate, for seven hours a day, a brood would consume 210 locusts per day, and the passerine birds of the eastern half of Nebraska, allowing only twenty broods to the square mile, would destroy daily 162,771,000 of the pests. The average locust weighs about fifteen grains, and is capable each day of consuming its own weight of standing forage crops, which at $10 per ton would be worth $1,743.97. This case may serve as an illustration of the vast good that is done every year by the destruction of insect pests fed to nestling birds. And it should be remembered that the nesting season is also that when the destruction of injurious insects is most needed; that is, at the period of greatest agricultural activity and before the parasitic insects can be depended on to reduce the pests. The encouragement of birds to nest on the farm and the discouragement of nest robbing are therefore more than mere matters of sentiment; they return an actual cash equivalent, and have a definite bearing on the success or failure of the crops. Year Book of the Department of Agriculture. There are exceptions to the above general rule, as is seen by the fact that locust-catching starlings breed in large numbers in localities where locusts have deposited their eggs. At seasons when the number of locusts hatched are few, many starlings die from lack of food. Not only do birds aid man in his battles with destructive insects, but seed-eating birds eat the seeds of weeds. This fact alone is sufficient to make birds of vast economic importance. Not all birds are insect feeders. Some, as the cormorants, ospreys, gulls, and terns, are active fishers. Sea birds also live upon shellfish, and crustaceans (as small crabs, shrimps, etc.); some even eat organisms of a lower grade of life. The kea parrot takes its meal from the muscles forming the backs of living sheep, while other birds of prey eat living mammals, sometimes of considerable size. Extermination of our Native Birds. Within our own times we have witnessed the almost total extermination of some species of our native birds. The American passenger pigeon, once very abundant in the middle west, is now practically extinct. Audubon, the greatest of all American bird lovers, gives a graphic account of the migration of a flock of these birds. So numerous were they that when the flock rose in the air the sun was darkened, and at night the weight of the roosting birds broke down large branches of the trees in which they rested. To-day hardly a single specimen of this pigeon can be found. Wholesale killing for plumage, eggs, and food, and alas, often for mere sport, has caused the decrease of our common song birds to one fourth of their former number within the past fifteen years. Every crusade against indiscriminate killing of our native birds should be welcomed by all thinking Americans. Without the birds the farmer would have a hopeless fight against insect pests. The effect of killing native birds is now well seen in Italy and Japan, where insects are on the increase and do greater damage each year to crops and trees. Of the eight hundred or more species of birds in the United States only two species of hawks, the great horned owl, the cowbird, and the English sparrow may be considered as enemies of man. The English Sparrow. The English sparrow is an example of a bird introduced for the purpose of insect destruction, that has done great harm because of its relation to our native birds. Introduced at Brooklyn in 1850 for the purpose of exterminating the canker worm, it soon abandoned an insect diet and has driven out most of our native insect feeders. Dirty and very prolific, it has worked its way from the East as far as the Pacific coast. this area the bluebird, song sparrow, and yellowbird have all been forced to give way, as well as many larger, birds of great economic value and beauty. The English sparrow should be exterminated. In Geographical Distribution and Migrations. Most of us are aware that some birds remain with us in a given region during the whole year, while other birds appear with the approach of spring, departing southward with the warm weather in the fall of the year. Such birds we call migrants, while those that remain the year round are called residents. In Europe, where the problem of bird migration has been studied carefully, migrations appear to take place along welldefined paths. These paths usually follow the coast very exactly, although in places they may take the line of coast that existed in former geological times. This seems to show that when a path has been established, it is handed down from one generation of birds to the next and so to successive generations. In this country the migration routes are comparatively unknown. It has been found that the Mississippi Valley, a former arm of the sea, forms one line of migration, while the north Atlantic seacoast is another route. There is opportunity for a careful observer to learn much of the spring or fall migrations in the particular part of the country in which he resides. All information thus obtained should be sent to the secretary of the American Ornithologists' Union or to W. W. Cooke of the Biological Survey, who has done much to establish what we already know about bird migration in this country. It has been recently proved by the Department of Agriculture that the southern movement of migratory birds in the fall of the year is not due entirely to the advent of cold weather. It is |