NORMS and DOHL: BEHAVIOR OF THE HAWAIIAN SPINNER DOLPHIN 



the entire range of school sizes observed. For 

 example, at various times number 24 was found in 

 schools varying from 7-10 to 120 animals, and 

 number 30 covered about the same school size 

 range, from 6 to 150 animals. Observations from 

 the MOC showed that on one occasion the same 

 subgroup, with the same general internal ar- 

 rangement of animals, persisted for at least 3 

 days. Many times, during three consecutive ob- 

 servation days (25-27 March 1970) the same sub- 

 group of five animals came to the bow of the 

 MOC. This sort of asssociation is well known in 

 captive schools and persists for long periods of 

 time (McBride and Hebb 1948; Tavolga and Es- 

 sapian 1957; and Bateson^). Such groups in cap- 

 tivity may be constructed of related or nonrelated 

 animals or even of animals of different species 

 (Bateson see footnote 5). Thus, while our observa- 

 tions of wild schools do not provide proof, we ex- 

 pect that some subgroup structure may persist 

 over long periods and that familial lineages may 

 be important, as has been observed in captivity 

 (Tavolga and Essapian 1957). 



The role of subgroups in larger dolphin schools 

 is apparently not simple. Such schools are not 

 simply composed of groups and subgroups that 

 themselves have cohesion. Instead, there are also 

 some assemblages that seem typical only of large 

 schools. For example, in large schools, groups are 

 often segregated. Groups of juvenile animals or of 

 mother-young pairs may be seen. Large schools 

 differ from one another by the presence or absence 

 of such groups. Some schools were composed only 

 of adults, while others had a high proportion of 

 young animals. Subgroups may move between 

 schools. Some social ordering, largely related to 

 growth and reproduction, may take place in 

 schools regardless of the origins of their con- 

 stituent parts. A major force in such ordering 

 within large schools may be the aggression of cer- 

 tain large adults, that may be either male or 

 female, who herd vulnerable gi'oups to central lo- 

 cations within the school (McBride and Hebb 

 1948). Such patterns have been proposed for S. 

 coeruleoalba by Kasuya ( 1972) and for S. attenuata 

 by Kasuya et al. (1974). 



AERIAL BEHAVIOR PATTERNS 



An experienced observer of spinner dolphins can 



^Bateson. G. 1965. The cetacean community in Whaler's 

 Ojve-Sea Life Park. 



quickly judge the activity state of a school by 

 watching its aerial patterns. It is possible to judge 

 the alertness of school members by checking the 

 kind and frequency of aerial patterns. In fact, such 

 analysis soon makes it obvious that the entire 

 sequence of changing behavior patterns through 

 any 24-h cycle is related to the level of activity, or 

 "emotional state," as indicated by aerial patterns. 

 Spinner dolphins not only "spin" but perform 

 several other clearly recognizable aerial patterns. 

 These include leaps, tail-over-head leaps, 

 backslaps, headslaps, noseouts, and tailslaps, or a 

 combination of these patterns — each performed 

 with variable vigor and frequency at various times 

 of day. 



The spin. The spinner dolphin rushes to the 

 surface as if about to make an arcing leap, and at 

 the last instant, when most of its body is out of 

 water, tips its flukes slightly and flexes its tail 

 stock, causing the airborn animal to spin about its 

 longitudinal axis. As many as four revolutions 

 may be made in the course of such a leap! Hester et 

 al. 1963). The dolphin may literally appear to 

 flicker as flippers, flukes, and the dorsal fin flash 

 by. The animal falls back into the water, usually 

 partly on its side, and its rapidly rotating body 

 scoops out a hollow of water around the sinking 

 animal. The hollow then collapses producing a 

 welter of spray (Figure 5) and a discernible clap of 

 sound. The spin is enhanced in air by postural 

 movements, in addition to the momentum ini- 

 tially imparted when leaving the water. Just as a 

 gymnast flexes his or her body or as a skater moves 

 elbows in a spin, the spinning dolphin flexes its 

 head and tail and moves its flippers toward or 

 away from its body (Figure 6). 



Spins are usually performed in a series of de- 

 scending intensity (as are other aerial patterns). A 

 given animal may spin as many as a dozen times in 

 succession, each successive spin generally being of 

 somewhat reduced intensity compared with the 

 last. The first leap may reach an apex perhaps 3 m 

 above the surface, while in the last of a series the 

 animal may not clear the water at all. Most spin 

 series are short, being composed of three or four 

 spins. 



All age-classes spin. It is not uncommon to see 

 small calves spinning repeatedly in moving 

 schools. In one case a young animal leaped into a 

 spin while in a feeding school, landing a dozen 

 meters off our bow. Each successive spin brought 

 the animal closer to us, as it was seemingly oblivi- 



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