Almost like giggling children, dolphins and whales squeal with delight when they get a fishy treat, a new study finds.
These marine mammals are known to use buzzing sounds to navigate and communicate when hunting for food. But the animals also emit victory squeals in response to a reward, or merely the promise of a reward, researchers say.
Sam Ridgway, president of the National Marine Mammal Foundation in San Diego, has spent most of his life studying beluga whales and bottlenose dolphins. He and his colleagues train the animals to do things by rewarding them with treats. [See video of dolphin squealing with delight]
"We noticed that each time an animal took a fish, it would make this particular pulsed sound," said Ridgway, co-author of the study, published Wednesday in the Journal of Experimental Biology.
The sound typically consists of a rapid series of pulses, usually with an upsweeping tone. Originally, he assumed the sounds were signals to fellow animals that food was nearby. But when his wife suggested the squeals resembled the sounds of joyful children, Ridgway decided to find out if she was right.
Ridgway and his colleagues trained bottlenose dolphins and belugas to perform tasks such as diving, and used a whistle or buzzer to signal that the animal would be rewarded later. The animals consistently made the squealing noises after hearing the signal, even long before the reward came.
To explore the phenomenon further, the researchers turned to brain chemistry. When a mammal gets a reward, it typically triggers a flood of the chemical dopamine to the brain's pleasure center. The researchers found that dolphins made their victory squeals 151 milliseconds after the reward signal, and belugas did so 250 milliseconds afterward. That suggested the animals were squealing in response to a dopamine surge.