nSHERY BULLETIN: VOL. 77, NO. 4 



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DESCENT 

 INTO 

 REST 



REST 

 PERIOD 



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AWAKENING 



9:30 10:00 10:30 11:00 



11:30 12:00 

 TIME OF DAY 



12:30 13:00 13:30 14:00 



Figure 14. — Trends in diving and surface times in a 40 animal school of spinner dolphins, Kealakekua Bay, Hawaii, 2 May 1970. 

 Breaks in record represent loss of the school by the ob.server, when a surfacing and descent was apparently missed. 



it moved back and forth across the width of the 

 bay. Its traverses sometimes took it nearly to 

 Kaawaloa on the north and to Keei on the south 

 (Figure 1). The various classes of aerial behavior 

 slowly disappeared in a rough graded series: the 

 most athletic patterns such as spins and tail- 

 over-head leaps first, then head- and backslaps, 

 then tailslaps, and finally all but an occasional 

 noseout was gone. 



School size and shape gradually changed at the 

 same time. The ranked school shifted into a sub- 

 discoidal shape and tightened markedly. For in- 

 stance a school of 30 animals that once formed a 

 spread rank over 75 m of water might become 

 concentrated in a 20 m diameter disc. Movements 

 became leisurely; in fact, the surface excursions 

 of the schools became almost surreptitious as the 



animals rose quietly from the depths, breathed 

 once or twice, and descended again. It became 

 very easy to overlook them, and two or three ob- 

 servers were needed to produce a complete record 

 of their dive sequences. During rest most time 

 was spent underwater (Figure 14). 



Vocalization was at a high level in arriving 

 schools and subsided as the rest period ap- 

 proached. Arriving schools made a variety of 

 noises including click trains, burst pulse signals 

 such as squawks or barks, and pure-tone whistles 

 or squeals. All but clicks ceased during rest. 



Rest 



During rest, quiet spinner dolphin schools 

 moved slowly back and forth, deep in the bay. 



840 



