MARSH WARBLER
to subordinate questions of æsthetic value to an inquiry as to the degree of specialisation attained by any particular song. In fact we must do so. For if we take our own conception of what is beautiful as the criterion of development, and say that the vocal powers of a certain species have reached a higher level of perfection just because the sounds produced appear to us the more pleasing, we manifestly postulate a direct relation between beauty and development, and assume that the bird forms an æsthetic standard analogous to that found in man. Such a method of approaching the subject might quite rightly be called in question. Must we then give up all attempts to interpret the vocal powers of birds in terms of development? Not necessarily. For if we try to conceive of a song apart from æsthetic emotion and the effect in us of association, all that remains upon which we can base our opinion as to its objective nature is the range of notes, the modulation, and the power of imitation displayed. But the imitative faculty is possessed by different species in different degrees; one bird, capable of but small power of song, introduces numerous notes of other species; another, having command of numerous strains covering a wide range, shows little imitation, whilst a third adds to numerous strains of its own an equal number of those of other species. No one would care to affirm that the Parrot or the Starling is a beautiful songster, yet each is capable of reproducing sounds of varying descriptions, and the former bird in confinement is said to imitate correctly songs having a proper musical notation. No one, on the other hand, would care to deny that the Nightingale is a beautiful songster, yet it indulges in but little imitation. So that the question is clearly beset with difficulties when we look at it from the evolutionary standpoint, and no useful purpose can be served by attempting to assign a definite position in a scale of development to this species or to that. We must take a broad view of the vocal powers as a whole, and perhaps we shall not be far wrong in provisionally accepting as the
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