THE LEARNING OF SONG PATTERNS BY BIRDS, WITH ESPECIAL REFERENCE TO THE SONG OF THE CHAFFINCH FRINGILLA COELEBS

SUMMARY 1. The songs and other vocalisations of birds are of theoretical interest to zoologists and psychologists (1) as social communication systems and as a “language”; (2) as specific and inter-specific recognition marks; (3) as a problem in the inheritance and genetical control of elaborate behaviour patterns; and (4) as a problem in the acquistion of complex behaviour patterns by individual learning. The last two constitute the main objects of this work. 2. The Chaffinch Fringilla coelebs was chosen as the main subject of investigation because its song displays both inherited and individually learned components, the relation between which is of particular interest. It is considered that neither a chain reflex type of theory nor one of reflex conditioning in the ordinary sense will provide satisfactory explanation of song production. 3. The characteristics and normal limits of variation of song of wild F. c. coelebs and F. c. gengleri are described and illustrated. There is no certain means of distinguishing the songs of these two subspecies but fairly consistent local differences occur. A wild male Chaffinch usually has more than one song type and may have as many as six. Full song is practically unknown in the female. 4. The song of insular species and sub-species and of artificially isolated populations tend to be simpler and less variable than examples from the Continent, possibly because, in a less dense population in an ecologically simpler environment, an individually distinctive territorial proclamation will not be so important for breeding success. 5. Experiments with F. c. gengleri were carried out in aviaries, bird rooms and cages. None of these techniques had any seriously adverse effect on the drive to sing. The onset of song could be controlled experimentally by crowding, by artificial control of daily illumination in a light-proof room and by injection of testosterone propionate. 6. Birds caught as juveniles in their first autumn and isolated until the summer following produced nearly normal songs that are almost as elaborate as are those of wild Chaffinches. If such birds, instead of being individually isolated, are kept together in groups in such a manner that they can hear only the songs of the members of their own group, these birds (as a result of counter-singing) copy one another and so come to produce a fairly uniform community pattern. Close matching of the final phrase of the song is particularly evident. 7. Birds which have been hand-reared in auditory isolation from the fifth day of life produce extremely simple songs which represent the inborn component of the specific song. If such Kaspar Hauser birds are themselves grouped together in isolated communities from the third to the thirteenth month of life, each group will-during the period February to May—build up, by mutual stimulation and imitation, complex but highly abnormal songs quite dissimilar from those of normal wild Chaffinches. From this it is clear that in the wild young Chaffinches learn some features of the song from their male parents or from other adults during the first few weeks of life. But most of the finer detail of the song is learnt by the young bird when, in its first breeding season, it first comes to sing in competition with neighbouring territory holders. There is little doubt that this is the way in which local song-dialects are built up and perpetuated. Full Chaffinch song is thus an integration of inborn and learned song patterns, the former constituting the basis for the latter. 8. The subsong of the Chaffinch is of low intensity, entirely different in structure from the full song, and contains a much bigger range of frequencies. It seems to have no communicatory function. It is characteristic of the early spring of first-year birds, and also of low but increasing production of sex hormones in birds of all ages. It provides in some degree the raw material out of which, by practice and by the elimination of unwanted extremes of frequency, the full song is crystallised. 9. The use of call notes, which are innate, as components of subsong and full song is described. Call notes are more evident in the songs of Kaspar Hauser birds than they are in the songs of normal birds. This is presumably an expression of the reduced auditory experience of the hand-reared isolated birds. 10. Chaffinches are not “imitative” birds in that they do not normally copy anything but sounds of Chaffinch origin. Once a Chaffinch has heard Chaffinch song as a young bird in the wild, it appears to have learnt enough about it to refuse to copy any sound pattern which departs far from the normal, i.e. it will learn only the fine individual variations of the songs of other Chaffinches. So, in the wild, Chaffinches practically never, in their full songs, imitate anything but other Chaffinches. Kaspar Hauser birds will learn songs of far greater abnormality provided the tonal quality is not too different from that of Chaffinch song. Voices as “abnormal” as that of a Canary may be learned by hand-reared birds and very occasionally by wild birds but when this happens the alien notes are kept as components of the non-communicative subsong only; the full song is not contaminated with them. If the tonal quality is sufficiently close to that of the Chaffinch, as with the song of the Tree Pipit and as with artificial songs constructed from genuine Chaffinch notes and played to the hand-reared birds by means of the “Song Tutor”, they will be learned at least to some extent and the learned pattern will become part of the bird's full song. 11. 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 outburst consists of a sequence of one song type followed by a sequence of another. This can be largely understood on the basis of the inter-action of the self-stimulating and self-inhibitory effects which are a concomitant of each song type. When songs are played back to a Chaffinch we find that those songs which it uses most frequently itself are the most effective in evoking song. 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. 12. It is suggested that with the more “imitative” finches such as Bullfinch, Hawfinch and to some extent Greenfinch, 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 resembles the subsong rather than the full song of the Chaffinch and similarly contamination with alien notes can be tolerated to an extent which might be highly disadvantageous in a highly territorial song. A preliminary study of a number of species of “Buntings” shows that many of the species, e.g. Reed and Corn Buntings (Emberiza schoeniclus and E. calandra) have songs which are highly stereotyped and completely innate. The song of the Yellow Bunting E. citrinella appears to consist of an integration of innate and learned components much as in the Chaffinch. The Buntings as a whole have highly territorial songs. 13. Apart from a very few and partial exceptions, Chaffinches can only learn song patterns during the first 13 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. This restriction of learning ability to a particular type of object and to a sharply defined sensitive period recalls the phenomenon of imprinting. 14. The inborn recognition and performance of the specific song pattern by the Chaffinch involves (a) duration of approximately 2 1/2 secs., (b) interval between songs of approximately 10–20 secs., (c) tonal quality (though this last may have been learned by the bird's experience of the qualities of its own voice). The readiness with which the bird learns to divide its song into three sections and learns to attach a simple flourish to the end as an appropriate termination suggests that there may be a very imperfectly inherited tendency to respond to and perform these features of the normal song which is revealed as soon as the singer is stimulated by hearing another bird.