Just as a pregnant woman may coo lovingly to her own belly, dolphin moms-to-be may talk to their calves before the little ones are even born. Speaking at the annual convention of the American Psychological Association in Denver, researchers from the University of Southern Mississippi said dolphins may start teaching their young to recognize their voices as early as two weeks before birth.

Dolphins and humans have a lot in common. Like us, they’re smart, social animals that rely heavily on sound to communicate. Each dolphin has what’s called a signature whistle: a unique noise that acts kind of like its name or call sign. Dolphin calves generally don’t come up with their own signature whistle until they’re about two months old. This may be so they can be sure they don’t choose a whistle that sounds too much like anyone else’s.

Previous studies had shown that, shortly before giving birth, pregnant dolphins start repeating their own signature whistles over and over. Some researchers theorized that the moms-to-be were trying to inspire their babies-to-be to develop their own whistles, but nobody was really sure. And while scientists had monitored moms before birth, nobody had yet continued the study after the calf was born. 

So doctoral student Audra Ames and her colleagues headed out to the dolphin enclosure at Six Flags Discovery Kingdom in Vallejo, California. A female dolphin named Bella was well into her pregnancy, and so they set up recording equipment to monitor the noises that she and others made. They captured 80 hours of sound in the four months surrounding the calf’s birth: two months before, and two months after [PDF].

Two weeks before the calf—Mirabella, or Mira—was born, Bella ramped up the amount of time she spent repeating her own signature sound, and she kept it up until Mira was two weeks old. Interestingly, at the same time, other dolphins in the enclosure quieted down, minimizing the sounds of their own names. As soon as Bella eased up on her signature sound, they went back to whistling their sounds as usual. 

Ames believes Bella was teaching Mira to recognize her mother’s voice—a form of bonding and imprinting. "We actually do see that human babies develop a preference for their mother's voice in the last trimester," she told Live Science. "We don't know if that's something that's going on here, but it could be something similar." 

That would explain the non-mom dolphins’ decision to keep it down. "What the other dolphins might be doing here is remaining quiet so the calf does not imprint on the wrong signature whistle," Ames said. 

Ames and her colleagues are currently studying other sounds made by mother-calf pairs.

[h/t Live Science]

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