FISHERY BULLETIN: VOL. 77, NO. 4 



Figure 9. — A headslap. The spinner 

 dolphin emerges belly down in the di- 

 rection of swimming and flexes its body 

 forward sharply at reentry. 



Noseout. The least active aerial behavior. The 

 spinner dolphin simply arches its back as it swims 

 to the surface, raising its snout into the air. It is 

 sometimes seen briefly when a resting school is 

 disturbed, or in schools where other, more active 

 behavior is occuring. It is often the first aerial 

 behavior seen in an awakening school. 



Tailslap. This pattern may be performed in 

 either the normal or the inverted position. With 

 the dolphin at the surface the tail is arched, bring- 

 ing the flukes above the surface. The flukes are 

 then brought down smartly against the water pro- 

 ducing a clearly audible sound. In the inverted 

 position an animal may sometimes scull along 

 making repeated and rapid tail slaps in a behavior 

 we have called "motorboating," because it not only 

 leaves a continous wake, but makes a "pop pop 

 pop" sound. An animal may slap 10 to 20 or more 

 times in succession in this way (Figure 10). A 

 whaler's term, "lobtailing," describes the same 

 behavior, but seems less descriptive than 

 "tailslap," a term now widely used by porpoise 

 trainers. 



What are the functions of aerial behavior? A key 

 point, we feel, is that each pattern, with the possi- 

 ble exception of the noseout, clearly makes noise 

 and, in fact, seems primarily structured to make 

 noise. For example, in a headslap the last compo- 



FlGURE 10. — An inverted tailslap by a spinner dolphin. 

 Tailslaps also may be made in normal body posture. Often a 

 series of a dozen or more slaps may be made at a single time, 

 which has been termed "motorboating" because of the white 

 wake and the sound produced. 



nent of the pattern is a rapid flexure of the trunk 

 and neck causing the chin and throat to slap 

 against the water. The tail-over-head leap effec- 

 tively slaps the flukes against the water with 

 great force. The spin scoops a cavity from the sea 

 surface whose walls collapse and thus produce a 

 sound we have heard both above and below the 

 water. Other aerial patterns are similarly struc- 

 tured. Such sounds probably radiate in all direc- 

 tions. Dolphin sound generation and beaming ap- 

 paratus, on the other hand, transmits sound in a 

 structured beam, directed forward (Schevill and 

 Watkins 1966; Norris and Evans 1967; Evans 

 1973). This beaming is better knovvTi for clicks 

 than whistles or burst pulse signals, though ap- 

 parently also true of the latter, at least in the 

 killer whale, Orcinus orca (Schevill and Watkins 

 1966). The directionality of clicks has been discus- 

 sed for S. longirostris by Watkins and Schevill 

 (1974). Thus, while vocal signals are directed al- 

 most wholly in certain sectors, the sounds of aerial 

 behavior are likely to approach omnidirectional- 

 ity. Our recordings indicate that none of the sig- 

 nals of aerial behavior propagate long distances. 

 Tail slaps may be the loudest. 



Aerial behavior is most frequent in fully active 

 schools in which the animals are dispersed, some- 

 times rather widely. In tight re.sting schools (see 

 below) sounds of all kinds except for desultory 

 clicking are nearly absent. Conversely, our obser- 

 vations of a captive spinner dolphin school held in 

 a community tank at the Oceanic Institute, Oahu, 

 Hawaii, showed that aerial behavior continued 

 through the night and, in fact, was most frequent 

 in the dark. Thus, high frequencies of aerial be- 

 havior seem correlated with conditions in which 

 many animals in the spread school cannot see each 

 other. 



Finally, these patterns are stereotyped by 

 species, and a trained observer can often visually 

 identify the genera or species of dolphins by their 

 aerial patterns, sometimes from long distances. 



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