W. H. THORPE 89 



iignihcant effect. The remaining three experiments (tive birds) gave a 

 negative result. 



The counter-singing that occurs between birds in adjacent territories is 

 an important factor in stimulating and restricting the imitative abilities of 

 chaffinches. When a chaffinch has acquired more than one song-type, each 

 song-burst consists of a sequence of one song-type followed by a sequence 

 of another. When songs are played back to a chatiinch, we find that those 

 songs which it uses most frequently itself arc the most effective in evoking 

 song (Hinde, 1958). A chaffinch in the wild will thus tend to reply to a 

 neighbour with that song of its own repertoire which most nearly 

 resembles the song of its rival. 



It is suggested that, with the more 'imitative' finches, such as the bull- 

 finch [Pynhuhi pyrrliiila), hawfinch [Coccothratistcs coccotliriiiistes) and to 

 some extent greenfinch [Cliloris cliloris), the song, while functional in co- 

 ordinating the breeding cycle and behaviour of the mated pair, is of less 

 importance as a territorial proclamation. Thus in some respects it re- 

 sembles the sub-song rather than the full song of the chafimch; similarly, 

 contamination with alien notes can be tolerated to an extent which might 

 be very disadvantageous in a strongly territorial song that must maintain 

 its character as a reliable specific recognition mark. A preliminary study of 

 a number of species of buntings shows that many of the species, for 

 example reed and corn buntings [Embcriza schociiichis and E. calaiidrn), 

 have songs which arc highly stereotyped and completely innate. The song 

 of the yellow bunting (R citriiiclla) appears to consist of an integration of 

 innate and learned components much as in the chaffinch. The buntings as 

 a whole appear to have strongly territorial songs corresponding to that of 

 the chaffinch in function. 



Apart from a very few and partial exceptions, chatiinches can learn song 

 patterns only during the first 1 3 months of life, and towards the end of 

 this time there is a peak period of learning activity of a few weeks during 

 which a young chaffinch may learn, as a result of singing in a territory, the 

 fine details of as many as six different songs. This special period of high 

 learning ability is brought to an abrupt close by internal factors. It matters 

 not whether a chaffinch has learned one or six songs by the time it is 

 13 months old, it can afterwards learn no more, and so remains with its 

 one song or its six for the rest of its life. This restriction of learning ability 

 to a particular type of object and to a sharply defined sensitive period 

 recalls the phenomenon of imprinting. 



The inborn recognition and performance of its specific song by the 

 chaffinch involves (a) duration of approximately 2^ seconds, (h) interval 



