Gregarious and athletic, Pacific white-sided dolphins (Lagenorhynchus obliquidens) are distinguished by their black backs, gray sides and white bellies. A suspender-like stripe runs down each side. Nicknamed “lags” after their unwieldy scientific name, these speedy swimmers rely on the up-and-down movement of their flukes, or flattened lobes of the tail, to propel them forward. Dolphins will eagerly ride the waves of a ship’s bow, and they have clocked speeds of up to 25 miles per hour.

Like belugas, dolphins use echolocation to navigate and to find food in murky waters. They send out high-frequency clicks that rebound off objects. The dolphin’s forehead and lower jaw pick up the returning sound waves, enabling it to interpret an object’s distance, size and shape.

Dolphins lack vocal cords. Muscles inside the blowhole produce the squeaks, moans, warbles and other sounds that you can hear our dolphins demonstrate. And each dolphin has a distinct whistle to identify itself, much like a name. But this chorus of sounds is not merrymaking. It’s communication. The vocalizations, as well as such behaviors as tail slapping, biting, or rubbing, may be a means of keeping track of one another, courtship, or alerting others to danger. Researchers are trying to translate the gestures. Whether humans ever crack the code, dolphins’ complex language points to their intelligence. The next time you visit Shedd Aquarium, listen for the distinctive sounds each dolphin makes.