•j6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



sionally, when both are separated from their foster parents in similar 

 circumstances and with the same degree of abruptness. 



(It is interesting that the vocal patterns uttered by infants who want 

 to attract or join their parents are similar to those of adults who want 

 to attract or copulate with their mates. This might suggest that the 

 sexual tendencies of adults develop from the infantile tendency to keep 

 in contact with parents.) 



The lowest intensity Hoots of infants (uttered toward the end of 

 a period during which Hoots have become progressively less frequent) 



5,000 i 



4.000 



3.000 



2.000 



1.000 





'■ > ' — — ' V » ■■» 



0.2 0.4 0.6 0.8 1.0 



Fig. 21. — A single "Brrrrp" sound, uttered by an immature. 



Based upon a spectrogram by a "Sona-graph." 

 This drawing does not show all the harmonics present. 



are relatively very soft and somewhat reminiscent, to human ears, of 

 the Moans of adults. The two types of patterns may be related 

 ontogenetically. 



The infant whose calls were recorded was heard to utter a few, 

 rather low-pitched, rattling sounds (see figure 21). These sounds 

 were relatively very rare, and were not heard to be uttered by other in- 

 dividuals. It seems probable that they were more or less "abnormal" 

 variants of some more common pattern. They sounded, to me, as if 

 they could be intermediate between High Trills and Gruff Grunts; 

 but spectrograms suggest that they were related to Hoots. They may 



