Killer Dolphins
killing these porpoises,' " Dr. Wilson told the Times. Other evidence quickly fell into place. Of the 105 porpoise post-mortems the team had done on animals found around the bay from 1991 to 1993, 42 showed clear evidence of dolphin attacks. The case was much strengthened after the team began finding people who had witnessed dolphin attacks. Observers twice saw the porpoises escape. Two apparent killings by a group of dolphins were captured on videotape. In 1996, the team published its findings in Proceedings of the Royal Society, a British journal. But still they did not know why the dolphins killed. Perhaps porpoises and dolphins competed for food, the scientists reasoned, or perhaps the porpoises were seen as a threat to young or ill dolphins. The killings of dolphin calves only deepened the riddle. The victims were roughly four feet in length - about the same size as the dead porpoises. In all, the team found five dead dolphin calves with fractured ribs, ruptured lungs and spinal dislocations. Again, witnesses and videotape aided the hunt for evidence. In one case, Dr. Wilson himself watched in amazement for 53 minutes as a calf was hit, seized and butted into the air by an adult bottlenose dolphin.
In all cases, the aggressor's sex was unknown. But the scientists speculated that the killers might be male dolphins trying to destroy rival offspring and free up females for mating. Females, the researchers say, become attractive to males within a few days of losing a calf and apparently, when tending youngsters, stay sexually inactive for years.
Infanticide is common in nature. Females kill their young when food is scarce and male lions and bears, for example, sometimes kill the young of a female taken as a new mate, giving them a reproductive and evolutionary edge. The Scottish scientists claimed this was "the first evidence of infanticide in cetaceans," the scientific grouping for whales, dolphins and porpoises. They speculated that the assaults on porpoises might develop "skills used in infanticidal attacks," or alternatively might stem from simple aggression or sexual frustration. Meanwhile, an American group was independently making similar discoveries as dead porpoises and baby dolphins were washing up along the Virginia coast, many with the telltale internal wounds. Suspicions were first aroused in 1997 when a baby dolphin was discovered with bruises, broken ribs and a lacerated lung. A check of specimens in 1996 and 1997 revealed eight
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