Vol. XXXVII 



1919 



Allen, Evolution of Bird-song. 535 



between the ordinary and the mating songs, the absence of con- 

 necting links. The Baltimore Oriole's ordinary song is not merely 

 a slight advance over the single song-notes; it is a much more 

 elaborate performance. If the former originated in the latter, 

 there must have been intermediate stages. What has become 

 of these? Why have they been lost in the process of song-evolution 

 while the single song-notes persist? Perhaps because they would 

 represent simply an inferior form of song and would have no place 

 in the Oriole's life, while the separate notes can be uttered easily 

 while the bird is feeding and can be used in a sort of conversational 

 way when he is not moved to utter a set song. There may be 

 similar reasons for the persistence in other cases of songs which 

 retain a place in a bird's repertoire, while other, more advanced 

 songs have given place to still others, still more advanced. 



There is another consideration. Some of the special "mating- 

 songs" are not merely more elaborate performances than the 

 "ordinary songs" and thus clearly an advance upon them; they 

 are ecstatic and confused, less orderly than the every-day songs, 

 and are interspersed with call-notes and chattering. This is the 

 case, sometimes at least, with the Baltimore Oriole. Such a song 

 in its present condition could hardly be expected ever to become 

 the regular song of the species. It would need to be modified and 

 regulated — standardized, so to speak. I see no reason why this 

 should not happen, but neither have I any proof that it does 

 happen. This whole question of the relation of these two types 

 of song to each other is a complicated one, and while I do not 

 believe that Mr. Saunders has settled it, neither do I claim to have 

 settled it myself. It may, indeed, prove that in this, as in some 

 other matters, no one formula will apply universally, but that the 

 nature and origins of the mating-songs are radically different in 

 some species from what they are in others. 



I have quoted Mr. Saunders as saying that " the ordinary song 

 [of birds possessing also a special mating-song] is evidently not 

 sung from sexual impulses, but is simply an outburst of vocal sounds 

 expressing great vigor and joy of living." It would be more exact 

 to say that the ordinary song is not sung from conscious sexual 

 impulses — using the word " conscious " in no strict sense, of course. 

 Those who believe with Mr. Saunders that " sexual selection is the 



