In nature species prey upon each other--the lowest forms of life upon inorganic and decayed matter, the higher forms upon the lower, the larger creatures upon the smaller, the savage upon the defenseless. Fertile lands not only produce luxuriant vegetation but teem with insect life, which, if not kept in check, would soon destroy that vegetation. In tropical and semitropical regions there are mammals, some of them quite large, which feed upon insects. In temperate regions where insects are not to be obtained during the winter, there would be no adequate check upon their increase and the consequent destruction of vegetation if it were not for the vast numbers of insect-eating migratory birds which come to these regions for the summer. Necessary as these birds are to vegetation on uncultivated lands, they are more necessary in cultivated fields, orchards, and gardens where the crops are more attractive to insects than the mixed vegetation on wild lands. As insect destroyers the domestic birds that are kept on cultivated lands only fill the place of the nonmigratory wild birds that have been driven away or exterminated. So it is to the interest of every one to protect insect-eating wild birds, for although these birds may do some damage to crops, their service usually more than pays for it. =Classes of domestic birds.= There are three classes of domestic birds--poultry, pigeons, and cage birds. The poultry class comprises land and water birds and contains nine kinds--fowls, ducks, geese, turkeys, guineas, peafowls, pheasants, swans, and ostriches. The pigeon class has but one kind, the pigeon, which is the only aërial bird domesticated for economic purposes. The cage-bird class has as its most important representative the canary. The other birds of this class have never been popular in America. The question of increasing the number of species of birds in domestication interests many people. There is a general impression among those not familiar with the commercial aspect of aviculture that many more species might be domesticated. While it is true that many birds capable of domestication have not been domesticated, there are few of these that would serve any purpose not better served by some species already domesticated. It will be shown as the different kinds and varieties of domestic birds are discussed that the most useful kinds are always the most popular, and that many others are kept principally as ornaments. The number of ornamental creatures that can be kept in domestication is limited, for as a rule animals, like people, must earn their living. CHAPTER II CHARACTERS AND HABITS OF BIRDS RELATED TO USE