At the root of this phenomenon is the well-known individual 

 variability of the voice, which is particularly well defined in birds. 

 A highly developed faculty for sound analysis and excellent coordina- 

 tion of the complex vocal musculature combined with the perfect 

 functioning of higher nervous activity are the most important 

 acquisitions of this group. The physiological mechanism of the highly 

 individual voice variability in birds also enables them to learn at an 

 early age and to imitate the sound elements of their environment. 

 Thus, the individual variability of the voice of a chaffinch indicates, 

 on one hand, the delimitation of its territory, and, on the other, 

 facilitates recognition between mates (Marler, 1956; Thorpe, 1961). 

 In this case the information communicated is primarily intended for 

 one's "own" mate and only to a lesser extent for another's. The 

 individual variability of the voices of penguins and other bird 

 species serve a similar purpose (Borror, 1959; Benson, 1948; Thieckle, 

 1961; Tembrock, 1959; and others). 



Experiments in raising birds under conditions of sound isolation 

 (Kaspar-Hauser isolation chamber), have shown that it is not so much 

 the song that is inherited as a certain rhythm, or way of rendition. 

 In ontogenesis the young bird creates its song with relation to the 

 sound background of its environment, which differs with each individual 

 and group of individual populating different territories. This mecha- 

 nism of song formation permits the delimitation of a territory, and 

 subsequently facilitates the recognition of a mate (Marler, 1956; 

 Thorpe, 1961). The acquired components influence the calls to a lesser 

 degree, but even they are influenced by differences in geography. 

 This somewhat simplified description becomes far more complicated when 

 one turns to experimental conditions that are as similar as possible 

 to natural conditions. This is demonstrated by the ecological in- 

 vestigations of A. N. Promptov and E. V. Lukina (1945). The majority 

 of species apparently inherit the basic ability to render a song, 

 including the general specific character, the tempo, and sometimes 

 even the pitch. All the other attributes and qualities are acquired 

 (Promptov, 1944). 



The establishment of a particular melody in a certain territory 

 is abetted by the fact that the development of the young male's song 

 is completed in the first spring of his life - that is, after his 

 arrival in the district, to which he will return all the following 

 years of his life by force of nesting conservatism. It has been 

 observed that the song of the chaffinch acquires its specific traits 

 as early as autumn; but it becomes more refined and finally stable in 

 the first breeding season (Thorpe, 1961; Marler, 1956). This develop- 

 ment of the song in spring lasts several weeks and undergoes no 

 subsequent essential change. Due to this prolonged development of the 

 of the song, the voice of every individual acquires the characteristics 

 of the group in whose territory the young bird has established resi- 

 dence. Its voice becomes more "comprehensible" to surrounding pairs, 

 even if the bird arrived as a "stranger," genetically unrelated to the 

 group living in the territory. 



