[Illustration: The English Pheasant] Although the pigeon is the only free-flying form which has been won to intimate relations with man, there are numerous other species of these volant creatures which have been reduced to partial domestication, though they cannot be trusted to abide with us without being more or less completely caged. Experience has shown that by far the greater part of the arboreal birds may be kept and will breed in captivity. From the host of these feathered creatures men have from time to time selected species which grace their habitations by their beauty, their song, or by the sympathetic relations which they form with their captors. Our successes in these efforts toward domestication of these birds have been most eminent with those varieties which in their wilderness state have a well-developed social life, which abide in families or flocks, and have the pairing habit well affirmed. The reason for this has been already indicated. It is due to the sympathetic motive which is developed in such communal life, and is manifested in the friendly relations with each other which the creatures maintain. A good instance of this is to be found in the crows and their kindred, a group of extremely sociable creatures, which are endlessly engaged in chattering communications with each other. All these forms are highly domesticable, and if for any reason they had proved permanently attractive to men they would doubtless have been brought into the state of willing captives. Although some of the free-flying or tree birds have been kept for their beauty alone, the greater part of them have commended themselves to man because of their voices. It is hardly necessary to tell the reader that the birds, of all animals, are most provided with means of expression through the voice. There is hardly a species which has not a greater range of notes or calls than the most vocal of our wild mammals, and many varieties are impelled to tuneful expression in a measure which no other creature, not even man, exhibits. In most cases these utterances are pleasing to the human ear, for they have the quality which we term musical. Therefore it is not surprising that the most of our captive birds have been chosen for their song.