isolating mechanisms of individual pairs and their groups. Yet they 

 provide the biogenic sound background of the biotope, landscape, etc., 

 with a highly specific character. It is well known that many wheat- 

 ears incorporate the screams of gerbils, susliks and many other species 

 into their song pattern (Varshavskii, 1959)- Warblers and mockingbirds 

 often imitate the voices of birds of prey. Consequently, the acquired, 

 the "learned" component can be utilized and already is utilized as a 

 finely differentiated zoogeographical criterion. 



In a number of cases the "learned" component in mockingbirds may 

 even be inherited, especially in those cases where too great a propor- 

 tion of foreign sounds in the song begins to interfere with communica- 

 tion. Thus, according to A.B. Kistyakovskii (1958), the crackling 

 musical phrases of the warbler have apparently become inherited by the 

 red-spotted bluethroat, and the whistling of the redshank ( Tringa 

 totanus ) by the skylark. 



Group (population) variability of the voice, manifested in the 

 above-mentioned local dialects, was described as early as the l8th 

 century by Thomas Ward, and was re-discovered by Lucanus in 1907» The 

 smallest groups recognizable by their local dialects sometimes occupy 

 territories of not more than a few hectares, and sometimes even less. 

 Described with the example of several species, especially of the 

 Isabelline Wheatear and of the red-headed bunting (by S.N. Varshavskii, 

 1959) a nd of the thrush (by A.S. Mai' chevskii, 1959); they are apparently 

 groups of closely related families of different taxonomic rank. It is 

 quite possible that some of them cannot be compared in size with the 

 basic population. Others, on the other hand, may correspond to the 

 basic and ecological populations. The local dialects of these small 

 groups are not stable. They have their own dynamics, they disappear 

 and re-appear, change with the territory, etc. In other words, they 

 are not yet fixed genetically, and are phenotypical phenomena. 



More stable are the dialects of large territorial groupings; ac- 

 cording to our own terminology - geographical populations. These 

 "vocal races" have been discovered within the limits of one subspecies, 

 and are not characterized by any systems . An excellent study was made 

 by F. Marler and M. Tamura (1962) on the voices of geographical popula- 

 tions of Zonotrichia leucophris , the white-crowned sparrow. The first 

 investigations of geographical differences of the chaffinch were made 

 by N.I.Dergunov (1925). Subsequently they were considerably enlarged 

 and supplemented by A.N. Promptov (1930), in a book which became a 

 classic, authoritative work. Geographical differences have already 

 been established in the singing of chaffinches in the surroundings of 

 Moscow, in the Southern Urals, in the Alps, the Mediterranean regions 

 and Greece (Promptov, 1930; Marler, 1956; Stresemann, 19^2; Sick, 1939; 

 Steinbacher, 1927). The rain-call of that species is also subject to 

 geographical variability. South German, Alpine and Mediterranean 

 blackcaps do not sing in the same manner (Sauer, 1955; Emeis, 1957 )• 

 Benson (19^8) found geographical variability in the voices of 33 

 species of passerines in Central Africa. Borror (1961) established 



