With their built-in smiles and sociable ways, common bottlenose dolphins (Tursiops truncatus) strike most of us as cheery, good-natured beings. But dolphins, particularly males, have a darker side. They battle each other to capture female dolphins, clobber unwilling female partners, and beat up (and sometimes kill) harbor porpoises. They also practice infanticide, killing newborn calves of females they have not mated with—a reproductive strategy that causes the female to become fertile a few months after losing her calf. Direct observations of these lethal calf attacks are rare. But a scientist witnessed one such incident on a newborn calf and mother, like the pair in the photo, in 2009 in Moray Firth, Scotland, which he reports in full in this month’s issue of Marine Mammal Science. A single male dolphin, known to the scientist’s research team as ID#021, swam rapidly into a group of 42 dolphins of mixed sexes. Among them were several mothers with their young calves. He targeted one mother and emerged from the group clutching her newborn calf in his jaws, writes the study’s author, Kevin Robinson. She and the others chased after him, as he butted, rammed, and pushed the calf deep underwater. The mother managed to retrieve her calf and surfaced with him lying motionless on her back. But the male seized the calf again, striking him with such force that he flew through the air. Other dolphins—males and females—came to the mother’s aid, and she was ultimately able to rescue her calf. But he was severely injured, and stranded himself 8 months later near Aberdeen, where he died. A necropsy revealed that he suffered from acute scoliosis—deformation of the spine—which the scientists believe was a result of the attack. In 2007, the research team reported that a high number of calves in the Moray Firth had these spinal deformities. They now believe they know at least one cause.