Ari S. Friedlaender/NMFS Permit

This is the sound a dolphin might hear if it’s about to become dinner

Not getting eaten is at the top of the to-do list for most members of the animal kingdom. Now, a new study suggests several species of dolphins can tell when they’re in danger of becoming a killer whale’s dinner—simply by eavesdropping on their calls.

Risso’s dolphins and short-finned pilot whales are frequently devoured when they live alongside mammal-eating orcas. To find out whether the dolphins can work out when they are in danger, researchers played recordings of killer whale calls underwater to 10 pilot whales off the coast of North Carolina and four Risso’s dolphins swimming near Southern California.

The animals didn’t respond to many of the killer whale sounds, but a subset of the calls provoked a strong reaction in both species: Risso’s dolphins rapidly fled, ending up more than 10 kilometers away from where the sounds were played. Pilot whales, on the other hand, called to each other and formed a tight group before diving directly toward the sound, the researchers report today in the Journal of Experimental Biology.

The calls that provoked the responses all contained multiple irregular features, such as harsh and noisy sounds or two distinct frequencies at once. The researchers hypothesize that these kinds of calls could be used by groups of killer whales to communicate during hunting—a clear sign for any potential prey in the area to take action.

“Normal” killer whale calls
Flight-provoking killer whale calls

The different responses of the two species probably reflect their social structures, the authors say. Pilot whales live in strong social groups that cooperate to fend off predators, whereas Risso’s dolphins—which have weaker social bonds—might find swimming away from a threat the better option. Either way, eavesdropping on predators seems to be very important for surviving the seas.