These Shark Bay dolphins are also viciously violent. When breeding season comes around, there is fierce competition for access to females, as happens in many sexual species. In most cases in nature, that competition is between individual males. The bottlenose dolphins have a different tactic: They form gangs.
Alliances are an essential part of the mating strategies of the males. First-order partnerships will single out a female, rush at her, and then herd her away to have sex, which is coercive (this is a general assumption, because it is rarely seen). During this aggressive corralling, the female repeatedly tries to escape, and does so in about one of every four attempts. The males restrict her attempts at freedom by charging in, and bashing her with their tails, head-butting, biting, and body-slamming her into submission.
Read: If you insulted a dolphin 20 years ago, he’s probably still bitter about it
Second-order alliances do the same, but the team-up makes a ratio of five or six males to one female. The males are often closely related in these alliances, so as a means of transferring their genes into the future, this fits perfectly well within evolutionary theory. On occasion, they form looser “super-alliances,” where multiple second-order gangs will join forces—up to 14 individual males—to corral a single female. These gangs don’t tend to be closely related.
It should be noted that forced copulation has not been directly witnessed, as far as I am aware. The evidence comes from observations of the precopulatory behavior, and physical evidence of violence on the females. Many people say semi-jokingly that in contrast to their cute and smart image, dolphins rape. There is no doubt that sexual coercion is part of their reproductive strategy, as it is in many organisms, and that the behavior is violent. But we must be careful not to anthropomorphize their behavior, whether it be cute, smart, or horrid.
Infanticide is another unpleasant behavior seen in dolphins. It often gets translated into murder in the popular press, but it should be noted that in plenty of other organisms, both males and females kill the young of others within their own species as a reproductive strategy.
A female lion lactates for more than a year when she is nursing cubs, and during this time won’t breed. Males acting alone or sometimes in packs will kill her young in order to bring her back to being fertile so they can then sire a pride. Mother-and-daughter teams of chimps in Tanzania have been seen killing and eating the babies of other parents for reasons that are not clear. Alpha-female meerkats will kill the litters of subordinate females so that they will be free to help nurture the alpha’s litter. Female cheetahs get around all these issues by copulating with multiple males. Their sperm mixes internally in the female, and she will give birth to offspring of several paternities in a single litter.