Craig, Exjyrrssioiis of Emotion in Pigeons. 6 1 



toeii-year-old boy. The first change observed is that the sibilant 

 notes of the young have become impure in tone. The impurity in- 

 creases until a decided harshness is produced, due to the admixture 

 of low tones with the high ones, making evident the analogy to the 

 breaking of the voice in a youth. The low tones become more and 

 more prominent and the high ones dwindle until, after many weeks, 

 the high tones have disappeared altogether, leaving the voice with 

 purely the adult sound. 



As to the age at which the change of voice occurs, there is an inti- 

 mation of the change, perhaps, as early as the age of four weeks, 

 for at that time the pure sibilant has changed to a squeaky tone, less 

 pure than the first, and louder. But the earliest distinct break in 

 the voice occurs at about six weeks. The following notation is to 

 represent the combination of high and low sounds which characterizes 

 the voice at this time. 



"" J^^ 'h.t^^ 



ksa ksa ksa ksa ksa 



Kali on alighting on perch. 

 Pitch of the "s" not definitely determined. The "a" is a hard chest-tone, 



impure. 



Each note begins with the sibilant sound but drops suddenly into 

 the lower pitch. As the bird grows older the sibilant is reduced more 

 and more, but many weeks elapse before it has entirely disappeared. 

 I have observed a slight trace of it in the alarm-note, for example, 

 at the age of seventeen weeks. 



The change of voice is due, no doubt, merely to the development 

 of the vocal organs, just as it is in the adolescent man. This puts 

 it on a different plane from the other developmental changes in ex- 

 pression. The inception of the fear reaction, of the alarm-note, of 

 the kah, or of the coo, and the changes in the form of the coo, must 

 be due to the coming into play of fresh tracts and centers in the 

 nervous system. But the deepening of the voice must be due to 



