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Males form alliances to consort with females, so female attractiveness can be measured by how many propositions she receives from males (Connor et al. 1996). Female bottlenose dolphins begin their menstrual cycle at 5-7 years of age and begin mating at 10-12 years of age (Schroeder 1990). Females may have 2-7 cycles per year, ovulate spontaneously, and are seasonally polyestrous. The varying cycle of the female may be responsible for the seasonal nature of consortships. Before ovulation, females have a period of 5-7 days of rising estrogen levels. Males have been seen to inspect the genitals of females by placing the snout within a few centimeters of the female’s genital area and making echolocation noises (Connor et al. 1996). With allied males, often one male approaches the female’s genital area from each side. This behavior is suspected to have the purpose of assessing the female’s state of fertility, whether in estrus, ovulating, or pregnant. Often, ovulating females are swollen in the genital region and male dolphins may use echolocation to detect this swelling. Another hypothesis is that males may taste the urine of the female to detect certain chemicals that indicate fertility (Connor et al. 1996).
Bottlenose dolphins exhibit preferential same-sex petting and rubbing. In a study by Mann and Smuts observing the development of bottlenose dolphins from newborn to juvenile, it was observed that 2-week-old male and female infants engaged in sociosexual rubbing (involving the genitals). Infant females were observed to engage in a keel-rub, a kind of rub common between male and female adults where the female swims belly-up under the male while rapidly flapping her tail, with older non-maternal females. Infant males did not keel-rub, but preferred rubbing of the erect penis, mounting, and even intromission with the mother. There was little contact between adult males and infants. As male dolphins grew older, they became more sexually active, mounting males and females of their own age as well as adults. Juveniles began to form same-sex alliances of peers and spend less time with their mothers, while females remained close to the mother-group (Mann and Smuts 1999).
Affiliative interactions increase bonding among members of a group. Male bottlenose dolphins in first and second order alliances engage in petting, where they rub each other with their pectoral fins (Connor 2007). One male may move his fin against the other or may provide a stiff fin on which the other dolphin may move. Petting is thought to reduce tension, caused by competition, among males (Connor et al. 2006).
Members of alliances often are synchronized in their breathing, coming up for air within 80-120 milliseconds of each other (Connor 2007). Within secondary alliances, synchrony is more common between primary pairs or trios. Connor et al. hypothesized that synchrony is a measure of alliance unity, meaning that more united alliances surface synchronously (2006). Synchrony is also a form of bonding and stress reduction visible in a decreased heart rate during contact (Connor et al. 2006).
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