74 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



by two or (less frequently) three short notes. Another common 

 arrangement is four or five short notes followed immediately by a 

 single long note. Other and more or less intermediate arrangements 

 also occur, but seem to be somewhat less common. 



Infants may "settle" on one particular type of mixed series, and 

 repeat it without variation in form for appreciable periods of time, 

 even when there is reason to believe that the strength of their motiva- 

 tion should be changing slightly. They sometimes seem to become 

 "stuck in the same groove." This would suggest that the utterance of 

 one type of series may facilitate repeat performances of the same 

 series, but does not facilitate, and may even discourage, subsequent 

 performances of different types of mixed series composed of the 

 same notes in different sequence. 



Some of the Screams and intermediates between Screams and 

 Squeaks uttered by infants may contain a hostile component like the 

 Screams of adults. The infant born and hand raised in captivity on 

 Barro Colorado Island uttered many Screams and related intermedi- 

 ate notes during the first few days after being taken from its parents, 

 a period during which it also performed an appreciable number of 

 overtly and unmistakably hostile reactions. Infants also tend to utter 

 Screams when handled somewhat roughly. But other Screams and 

 intermediate notes are almost certainly not hostile. It was very com- 

 mon, for instance, to hear a captive infant which had accepted human 

 beings as foster parents utter many notes of this type in immediate 

 association with both Squeaks and Hoots (see page 75) when left 

 alone. These notes were not accompanied by any trace of overtly 

 hostile movements or Gruff Grunts, and both the Squeaks and the 

 Hoots were certainly provoked by the thwarting of the infant's de- 

 sire to be with its foster parents. It seems likely, therefore, that 

 at least many of the patterns intermediate between Squeaks and 

 Screams are similar to the former in being generalized distress reac- 

 tions. This, and the complete intergradation between the two extreme 

 types of patterns, would suggest that the Screams of infants are little 

 or nothing more than the highest intensity form of their Squeaks. 

 (It would not, in fact, be necessary to give the patterns different 

 names if they were not so distinct, in both form and causation, when 

 uttered by adults). 



The captive infants uttered High Trills when approaching their 

 food dishes and feeding, and also when I lifted them up and brought 

 their faces close to mine. This would suggest that their High Trills 

 were produced by the same motivation as some or all of the Trills of 



