Elephant seals will help scientists keep an eye on very secretive marine mammals in the deep ocean.

About a decade ago, a group of biologists stuck recording devices on the backs of several elephant seals off the coast of California. They wanted to know if seals, whose males are easily recognizable by their cartoonish faces with trunk-like noses, make sounds when they swim out to sea in search of food.

The records they brought took the researchers by surprise. There was no evidence that the seals made sounds while feeding, but the devices picked up something else: the eerie clicking calls of the cachalats that sound like someone is walking up a creaky staircase. Some of the sounds seemed to get louder, leading the researchers to believe that the seals were swimming towards the whales and,

The discovery didn’t do much, but it did inspire marine biologists to use seals as a tool to eavesdrop on other marine life. Elephant seals spend about nine months a year at sea and travel to the far reaches of the Pacific Ocean, which are quite difficult for scientists to explore. And like migratory birds, seals return to the same spot year after year, allowing researchers to equip them with recording devices and retrieve them relatively easily.

As early as next week, marine biologists from the University of California at Santa Cruz (UCSC) will test this method. They will attach acoustic monitors to several northern elephant seals before the animals leave for just over two months on their voyage.

If all goes according to plan, for the first time, scientists will use animals—rather than a network of underwater microphones—to monitor marine life in the deep ocean for longer than a few days. What they overhear could help scientists unravel the mysteries of elusive marine mammals – such as beaked whales – and understand how little-studied ecosystems are changing as the planet warms.

Scientists have been using recording devices to monitor marine life for decades. This is a common way to study species such as the rare vaquita porpoise. What is unique about this project, however, is that these devices will not be fixed in place or dangling from the boat – they are attached to animals.