NORRIS and DOHL: BEHAVIOR OF THE HAWAUAN SPINNER DOLPHIN 



probe the genital area of another einimal, and the 

 upper animal sometimes rode along with the dor- 

 sal fin of the lower animal pressed into its genital 

 area. Mating postures were commonly seen, most 

 often in alert schools early in the morning or near 

 dusk. On one occasion (in captivity) we were able 

 to determine that both partners in such a pair 

 were males, even though females were present in 

 the tank. We were able to confirm heterosexual 

 contact in some pairs in nature. Tj^pically, one 

 animal swam in the normal upright orientation 

 while another swam upside down, with the genital 

 areas of the two pressed together. Either sex could 

 be above or below. Intromission was usually 

 difficult to see, but was noted on occasion. Contact 

 was sometimes maintained for several seconds. In 

 some observations the upper partner was rela- 

 tively quiescent and propelled itself with fluke 

 strokes of much reduced amplitude compared 

 with those of normal swimming. One mating 

 chase was noted as a school moved onto the feed- 

 ing grounds off Keauhou, the pair raced by the 

 bow of our vessel as we travelled at an estimated 

 4 kn. They dove and spiralled swiftly together. 

 The coupling and synchrony of movement of the 

 pair was so perfect that the two animals were not 

 evident until the pair turned on its side. Together 

 they veered away from the bow, diving about 20 

 m down and remaining in the coupled position for 

 several seconds. We heard whistling with the un- 

 aided ear when such coupled animals were near 

 the ship. 



A particularly complete observation of mating 

 was made from the MOC on 26 July 1970, at 

 Kealakekua Bay. A male-female pair swam di- 

 rectly in front of the viewing capsule, and the 

 female swung under the male until their ventral 

 surfaces were in contact. The penis of the male was 

 seen to enter the female, though no thrusts were 

 noted as the position was held for 3-5 s, while the 

 smimals glided without fluke strokes, and then the 

 animals parted. Shortly, the female again moved 

 under the male, but no further intromission ap- 

 peared to take place. Instead, the male accelerated 

 with a few fluke strokes, and the pair cruised off, 

 side by side. 



Competition for partners was occasionally ob- 

 served. On 29 March 1970 at Kealakekua Bay, the 

 MOC entered a school of 12-13 animals, and 2 were 

 noted swimming upside down. Both pursued and 

 came up under a single adult above them. Later, 

 three inverted animals pursued two in the normal 

 swimming posture. At that moment another large 



adult swam rapidly to the moving group and force- 

 fully inserted itself between one inverted animal 

 and the one above it. The upper animal then dove 

 away from the group, with the intruder following. 

 The two inverted animals moved quietly, main- 

 taining their upside-down orientation, toward 

 another nearby animal swimming in normal 

 orientation. 



Observations of captive spinner dolphins show 

 that much social interaction is sexually related 

 and that it may occur between animals of all age 

 classes and combinations of both sexes. As has 

 been found in the Atlantic bottlenose dolphin, 

 Tursiops truncatus, sexual behavior and social 

 communication are interwoven to such an extent 

 that it is often impossible to separate true court- 

 ship and mating behavior from communicative 

 behavior of other sorts. For example, Caldwell and 

 Caldwell ( 1967) reported a 2-day-old male Atlan- 

 tic bottlenose dolphin having an erection when 

 brushed by its mother. Sexual maturity is not 

 reached in the spinner dolphin until a minimum of 

 3.7 yr iPerrin et al.*) and even later in the 

 bottlenose dolphin, and thus one must view this 

 precocious use of sexual patterns as part of the 

 development of communication concerning rela- 

 tionship. Such communicative use of sexual pat- 

 terns has been reported for mixed schools of cap- 

 tive spinner and spotted dolphins (Bateson see 

 footnote 5). 



Other Social Patterns 



Contact, not necessarily sexual in context, is 

 common between members of dolphin schools. 

 When groups of animals swam near the viewing 

 capsule, one could often see animals touching one 

 another writh the tips of pectoral fins, the dorsal 

 fins, or fluke tips. Jostling or pushing of animals 

 near the capsule often occurred and was accom- 

 panied by sound emissions. Such jostling can be 

 seen commonly in other bowriding groups. Be- 

 cause a few animals from a given school seem to do 

 most of the riding and some seem to occupy specific 

 places at the bow, one gains the impression that 

 hierarchical relations in the school are involved. 



The release of air may correlate with social sig- 

 nals in spinner schools. Commonly, long streams 



'Perrin.W. F.,D. B. Holts, and R.B.Miller 1976. Growth 

 and reproduction of the eastern spinner dolphin. A geographical 

 form ol Stenella longirostns in the eastern tropical Pacific. U.S. 

 Dep. Commer. NO.AA. Natl. Mar. Fish. Serv., Admin. Rep. LJ- 

 76-13, 84 p. 



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