most economical action .of the sound-receiving apparatus". This places the matter on a purely mechanical and automatic basis, although the results are what we may call aesthetic. The results, I believe, are not unappreciated by the singer, and he re-acts with a more conscious exercise of "artistic taste". I believe, in short, that the actual superior musical quality of the House Wren's song, consciously appreciated by the Brown Towhee, is the final factor in the selection of it instead of the harsh "cracker" of the California Woodpecker, the yelping "klee-yuh" of the Flicker, and other more or less unmusical sounds in the list. But for further discussion of this theory I refer my reader to the final section of this paper. And now let me pass to the next division in order, namely:
3. The fact of elaboration through adding the imitated syllables at the end.—An analysis of the two Brown Towhee songs which are the subject of this paper reveals that they are the stereotyped song of the species plus some acquired syllables. The acquired syllables in each case occur at the end of the stereotyped song. Now, this manner of elaboration is, it seems to me, the easiest and most natural one—the one which a bird taking its first clumsy steps in the direction of song improvement would of necessity employ. Even human beings are inclined to have "single-track" minds that cannot easily accommodate two thought-trains abreast. They wish to do "one thing at a time"; otherwise they are apt to become flustered and end by doing neither of the two things intended. It seems perfectly natural that the Brown Towhee should sing the old familiar song first, and then give his undivided attention to innovating. Reverse this technique and we immediately picture the bird so flustered at his attempt to plunge directly into a radically different type of utterance that he would not be able immediately to pass on to the regular syllables. The accustomed song is the momentum, the encouragement, that carries him into the less familiar performance.
Witchell (p. 192) quotes Bechstein to the effect that the (European) Redstart "can improve its song … by adding to it parts of the songs of birds that are found near it". He vouches for the fact that Bechstein "accurately records that the Redstart adds the notes of other birds, for the imitations of this species are uttered at the end of the ordinary strain, to which they form a kind of sotto voce suffix".
The Redstart, then—even though mimicking a goodly number of other birds (Witchell, p: 218)—nevertheless adds the mimicked notes amateurishly (as I may call it) at the end, even as does the Brown Towhee. Both Redstart and Towhee, it would seem, axe in the practice stage of mimicry, as opposed to the more advanced stage attained by the Mockingbird who interpolates imitated passages at will with all the assurance and independence of a human improviser. In England, it would seem, there are a number of such accomplished and evolved mimics, including the Thrush, the Robin, the Skylark, the Starling, the Sedge-Warbler, and the Nightingale (Witchell, pp. 194-219). In fact, one gathers the impression that mimicry is quite the thing in the best English song-bird circles!
4. The fact of the comparative musical quality of the imitated syllables.—The fact that the imitated portions in both of our two "off" Towhee songs, though borrowed from two different birds, nevertheless both contained a liquid r-sound and a vowel-sound of decidedly lower pitch than the piercing, high-frequency i-sound emanating from the traditional tip! of the species, suggests the idea that, other things being equal, the Brown Towhee is interested in sounds of a more fluent and of a softer nature than those used in his ordinary song.
