Researchers pouring over 52 years of observations have discovered that dolphins and beluga whales actually squeal with delight when they’re rewarded with tasty fish treats. Insert squee!! (rather, eeeeeeee!!) here. The findings were published in the Journal of Experimental Biology this week.

Sam Ridgway of the U.S. Navy’s Marine Mammal Foundation has worked with cetaceans since the 1960s. Whether studying how deep they dive or how depth affects their hearing, he’s always trained the animals with food rewards. They’d squeal a high-pitched “eeeee” each time they received their treat; sometimes they’d emit the sound in sheer anticipation. Ridgway had thought that these were food signals, he tells Inside JEB, that the animals were communicating the presence of food to others in their population nearby. But maybe not... after all, the sound reminded him of a child’s happy squeal.

To see if these were genuine expressions of delight, Ridgway and an all-San Diego team examined decades-worth of recordings from experiments where bottlenose dolphins (Tursiops truncates) and belugas (Delphinapterus leucas) were trained for various projects -- paying particular attention to their “victory squeals.”

Animal trainers often couple rewards with a sound, like a buzz or a whistle. When the task is mastered, the trainer stops giving out food and uses just the sound to let the animals know that they performed successfully and to expect a treat later. Even without a food reward, the cetaceans squealed in response to the sound. “The behavior had transferred over to another stimulus that wasn't food,” Ridgway explains.

Additionally, the researchers also trained two belugas rescued from Canada and four dolphins from the Pacific and the Gulf of Mexico to dive below and turn off an underwater buzzer by pushing a button. They made victory squeals right afterwards.

Ridgway suspects it has something to do with the pleasure chemical dopamine. Back in the 1950s, researchers showed how animals appeared to derive delight from electrical stimulation of the brain region that releases dopamine -- as much so as they did with a food reward. In lab animals, a dopamine release takes 100 to 200 milliseconds. So, the team measured the delay between the trainer’s signal and the observed victory squeals. If the delay between the promise of reward and the squeal was longer than the dopamine release period, that would likely mean that the animal was expressing pleasure.

They found that dolphins take an average of 151 milliseconds of extra time for this release, and the belugas showed a 250 millisecond delay. Though the researchers didn’t directly measure the neurotransmitter in the brain, Science explains, that’s enough time for dopamine to spark the sound.

Looks like victory squeals may have an emotional content after all. You can listen to a dolphin’s victory squeal after it closes in on a fish in this video.

[Via The Company of Biologists]