It’s easy to think that dolphins aren’t dangerous. They have such a nice smile. They perform on command. And people can even pay a bunch of money to swim with them.
But in the wild, dolphin life is full of violence. And that violence can start just after birth, a new study shows. Scientists witnessed a wild bottlenose dolphin birth — a first, at least, to be recorded in a scientific journal — only to watch as two males tried to kill the calf. They report the event July 14 in Marine Mammal Science.
On August 23, 2013, three boatloads of scientists were searching for bottlenose dolphins near Tybee Island, Georgia. Shortly after 10 in the morning, some of the researchers spotted a female flanked by two males. An hour and a half later, the female was in a group of five dolphins, including the two males. There was some thrashing, and the scientists spotted a baby dolphin and some red fluid — blood from the placenta — coloring the water. The calf had just been born.
In the next minutes, the two male dolphins approached the mother and baby. They pushed the calf underwater. They leapt out of the water, landing on the baby. “The surface behavior was chaotic with considerable thrashing and white water,” Robin Perrtree of Savannah State University in Georgia and colleagues write. (A short video is available online.) Over a 23-minute period, they saw four attempts to submerge the calf, who was luckily rescued by mom again and again.
The researchers backed off to give the new mom some space. That meant that they didn’t have a good view of what went on in the hours afterward. But they made acoustic recordings of the dolphins. They could hear low-frequency sounds that they think were the aggressive noises of the attacking males. They could also hear a high-pitched whistle, probably from mom. The attack had continued, even though none of the researchers could see it from the surface.
The pair of males may have been tracking the mother before she gave birth, waiting for the calf to emerge. And although the researchers can’t say for certain what the males’ intent was, the older dolphins were certainly a danger to the newborn calf. One reason, the scientists speculate, is that the males wanted to kill the calf to make the female available for mating.
Scientists have spotted instances of dolphin infanticide in the wild before, but in those events, the calf was always tossed into the air. In one case where the calf didn’t die, it was later found to have acute scoliosis, possibly due to injuries received in the attack. If such attacks are often conducted underwater, as happened in August 2013, infanticidal behavior may be more common than previously believed, the researchers say.