W. H. THORPE 8l 



incapable of auditory learning under the conditions oi the experiment, and 

 this striking failure in a species whose wild ancestors arc closely related to 

 the wood duck is supposed to be a consequence of domestication. Klopfer 

 (1959) then studied the following-responses of European shelduck 

 [Tadorua tadoriia). Young oi^ the species hatched and reared in sound- 

 proof rooms showed no tendency to approach repetitive sound signals 

 when tested at 18-26 hours of age. In this they were similar to wood ciucks 

 and domestic muscovies, and unlike any species of surface-nesting water- 

 fowl. However, with the shelduck, exposure to repetitive sound signals in 

 early life produced no change in the response pattern, whereas in the wood 

 duck it did so. Nevertheless, associating the sound signals with an object or 

 person which the ducklings were allowed to follow for short periods 

 enabled a highly specific preference for sound to be developed, and in this 

 shelducks resembled several species of surface-nesting waterfowl, particu- 

 larly of the genus Auas. Of course this work does not prove that there are 

 no sounds to which these birds would respond in the absence of visual and 

 motor experience, but it does appear that a preference can be established 

 for sounds which are linked to a visual model. As in the surface-nesters, 

 one can suppose that the following-response serves as a necessary rein- 

 forcement in the learning of particular sound signals. Thus the behaviour 

 of the young shelduck does not show the pattern which would seem to be 

 most appropriate for hole-nesting species, for whom auditory stimuli 

 should be of much greater importance than visual ones. Moreover, hole- 

 nesting species should either be endowed with response tendencies to 

 specific auditory stimuli at the time of hatching, or else highly susceptible 

 to auditory imprinting. That, for instance, seems to be true of the wood 

 duck. It would thus seem likely that newly hatched shelducks emerge 

 from their burrows in response to visual or perhaps tactile stimuli, with 

 auditory cues assuming a secondary importance. The fact that shelduck 

 will nest in thickets above ground when burrows arc not readily available 

 also suggests a possible explanation tor this difference in behaviour. Here 

 is an interesting opportunity for a held investigation which will be 

 essential before the whole matter can be completely understood. 



In nidicolous birds this particular type of following-response cannot, of 

 course, operate. Nevertheless there is in certain song birds good evidence 

 for something very suggestive of imprinting in the process of learning 

 characteristic song, and indeed the vocalizations of birds can be regarded 

 as offering particularly crucial problems concerning the acquisition of 

 complex behaviour patterns as a result of individual learning. 



The normal song of the chaffinch is an elaborate integration of inborn 



