°'l9i9 J Allen, Evolution of Bird-song. boo 



song has been evolved from the ordinary song, from which it has 

 never quite succeeded in freeing itself, than that the warbling song 

 should first have developed the teacher teacher teacher strain, and 

 that then this new and comparatively uninteresting strain should 

 have been selected to be lengthened and strengthened into the 

 ordinary song of the species? 



Another common Warbler, the Black and White (Mniotilta varia), 

 possesses a song which is confined, I think, to the nesting-season, 

 and this is so like the ordinary song of the species that the two 

 must certainly have had a common origin. The song we first hear 

 from newly arrived birds in the spring is a plain wee-see wee-see 

 wee-see wee-see; then later we hear what is obviously the same 

 song elaborated by lengthening the performance and lowering the 

 pitch of two of the dissyllabic notes near the end, thus: wee-see 

 wee-see wee-see wee-see woo-sce woo-see wee-sec wee-see. This lat- 

 ter song is uttered from a perch and is not an ecstatic perform- 

 ance like the Ovenbird's, but it is clearly a mating-song as dis- 

 tinguished from the ordinary song, and it is equally clearly an 

 elaboration of that song. Of course, it may be argued that the 

 more elaborate song is the regular one, and the other, which is 

 heard first, is only a shortened, abortive form of it, used before 

 the song-impulse has gained its full force; as, in the autumn, when 

 the song-impulse is waning, we hear often only the introductory 

 notes of the White-throated Sparrow's song; but is it not probable 

 that in both these cases the shortened form is merely a reversion 

 to an ancestral song, the song as it was before it was evolved into 

 its present complete form? The ordinary course of evolution is, 

 of course, from the simple to the complex rather than from the 

 complex to the simple. 



Again, the long-continued, richly intricate song that we hear 

 from the Rose-breasted Grosbeak (Zamelodia ludoviciana) in the 

 height of courtship excitement is obviously only an elaboration 

 of its ordinary song. 



Is it not reasonable to assume that courtship excitement should 

 lead to a more and more elaborate form of song-expression as the 

 development of the species goes on, and that the song of the more 

 excited moments should always be somewhat in advance of the 

 ordinary song in point of fervor and elaboration? This view of 



