biologists have suggested, only two or three males monopolize all copulations). Males that do not form same-sex pairs may have a more exclusively heterosexual orientation. Female Bottlenose Dolphins probably have a similar pattern of bisexual interactions overlaid on a largely female-centered social framework. Spinner Dolphins seem to be more uniformly bisexual without extensive periods of exclusive homosexuality, often alternating between same- sex and opposite-sex interactions in quick succession (this sort of concurrent bisexuality has also been observed in Bottlenose and Atlantic Spotted Dolphins). In captivity, though, Spinners exhibit a continuum, with homosexual activity making up only 10 percent of some individuals’ behavior, half to two-thirds for other animals, while some Dolphins interact almost exclusively with animals of the same sex.
Nonreproductive and Alternative Heterosexualities
Nonprocreative activities are a hallmark of Dolphin heterosexual interactions. Virtually all of the nonreproductive behaviors described above for same-sex interactions also occur between males and females, including beak-genital propulsion and stimulation of the genitals with the flippers, flukes, and snout. Group sexual activity—much of it heterosexual but nonreproductive—occurs in Spinner wuzzles, and courtship and sexual activity in Bottlenose Dolphins sometimes involves up to ten animals at a time. Female sexuality in Dolphins is often pleasure-oriented, focusing on stimulation of the clitoris as much if not more so than vaginal penetration and insemination. Bottlenose Dolphins mate and interact sexually at all times of the year, not just during the mating season; in Spinner Dolphins (and other species as well), males have a yearly sexual cycle, with significant periods when they are probably unable to fertilize females. In addition, masturbation is a prominent feature of Bottlenose sexual life: both males and females rub their genitals against inanimate objects or other animals, sometimes even developing the activity into a playful “game.” Females have even been observed using the muscles of their vaginal region to carry small rubber balls, which they then rub their genitals against. Young Dolphins are sexually precocious, and incestuous copulations have been observed between males a few months old and their mothers. Both male and female Bottlenose Dolphins also interact heterosexually with Atlantic Spotted Dolphins, often using the same sideways mounting position and aggressive behaviors described above for interspecies homosexual encounters. Adults often direct sexual behaviors toward juveniles during these interactions, and female Bottlenose Dolphins have even been seen sideways mounting younger male Spotteds (REVERSE mounting). Many heterosexual interactions in captivity also take place between Dolphins of different species.
Interestingly, this broad variety of heterosexual expression takes place in a larger social framework of primarily separate spheres of activity for males and females, at least in Bottlenose Dolphins. As described above, the two sexes are largely segregated for most of their lives, often socializing in same-sex groups. Furthermore, many animals spend a large portion of their lives uninvolved in breeding: most males do not begin mating until they are at least 20 years old (well beyond the time they become sexually mature), and many Dolphins of that age still do not participate in heterosexual mating. Females breed only once every three to six years, and nearly a quarter of the adult female population may not be involved in reproductive activities at any time. When females do bear calves, they are often assisted by another adult—usually a female—who acts as a “baby-sitter,” taking care of the calf while she feeds. Males do not generally parent, and indeed, most Bottlenose calves are sired by males from outside the community. In Spinner Dolphins, “helpers” may be of both sexes, and parental helping behavior has also been observed between Dolphins of different species, for example, by adult Common, Spotted, and Spinner Dolphins toward Bottlenose calves. At times, however, this behavior (within the same species) may be less than “helpful,” especially when it involves males. In captivity, “baby-sitting” males have been observed harassing mothers, trying to “kidnap” their calves, and even behaving sexually toward the infants (including trying to mate with them). Pairs and trios of males in some Bottlenose populations also occasionally harass adult females, chasing, herding, and even “kidnapping” and attacking them (e.g., with charges, bites, tail slaps, and body slams) in an attempt to mate with them. Recently, infanticide has also been discovered in some wild Bottlenose communities.
Other Species
Homosexual activity has also been reported in (captive) male Harbor Porpoises (
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