The dolphins that swapped babies

As researchers eavesdropped on two new dolphin mothers, they were surprised to find that one took the other's calf

Recognising a mother's call is one of the earliest and most important life lessons for a dolphin calf.

They can easily be separated from their mothers in the vast open ocean, so listening out for her call means they could quickly reunite.

But just how early a calf learns its mother's call was not fully understood. In a new study of bottlenose dolphins, researchers listened in on two captive dolphin mothers to understand how mother-calf recognition develops.

They discovered that the mothers rapidly increase their unique "signature whistles" as soon as the calf is born.

They whistle up to five times more than usual. But they also saw the mothers do something completely unexpected.

"We were surprised at how strong the results were," says Stephanie King of the University of Western Australia, who led the research at the Dolphin Research Center, a sea pen facility in Florida, US.

"We call this 'vocal imprinting', where the calf imprints on its mother's signature whistle," says King.

"It's an important learning phase where the calf learns to recognise its mother, and it's important this happens quickly before mother-calf separations occur."

It was already known that it takes a calf several months to develop its own unique call. "They are not born with a signature whistle, they learn it," says King.

Until they do so, they have to listen closely to find their mothers. This work, published in the journal Marine Mammal Science, reveals once again how vital sound is to a dolphin's world.

Two weeks after the calves were born a surprising turn of events took place.

The two mothers, who are also sisters, swapped babies. Or rather, the older sister, Pandora, forced the switch.

Read the full article here