Bottle-nosed dolphins have long had the image of being intelligent guardians of the sea who speak their own language, enjoy the company of humans, and have even saved shipwrecked sailors from certain doom by leading them to land. Although these frolicking mammals may look friendly with their toothy smiles and playful gestures, marine biologists in mid-1999 were learning that dolphins also have a dark side that may include the capacity to kill.
In Shark Bay, on the coast of Western Australia, researchers from the University of Massachusetts in Dartmouth have observed gangs of male dolphins harassing and intimidating sexually receptive mature female dolphins. The researchers, led by biologist Richard Connor, documented several cases in which male dolphins, working in groups of twos and threes, “kidnapped” females from other dolphin groups. The females were then held captive for as long as one month.
However, Connor said that his research found no evidence that male dolphins ever forced female dolphins to mate. In fact, some females did not seem to be bothered by being herded around by their male cohorts. But by outnumbering the females, Connor said, the male gangs do bully, and may injure, females with powerful blows from their beaks or sharp teeth. Such aggression is not uncommon in mammals. But what amazed Connor and his colleagues was how organized the dolphins' aggressive behavior was. Connor said the herding of females by male gangs may be, in part, a reaction to female promiscuity. Biologists know that female dolphins are very sexually active and may want to mate with as many males as they can. Some researchers thus speculated that herding by male gangs is a strategy to prevent females from reproducing with rival dolphins.
