Animals That Eavesdrop: How They Use Listening to Survive

While humans may have perfected the art of eavesdropping—even at great distances—humans aren’t the only animals capable of eavesdropping on conversations around them.

Robert Magrath, an ornithologist and behavioral ecologist at the Australian National University, has co-authored several studies on interspecies communication in birds. Much of his research has involved bird sirens: the sounds birds make outward when they spot a predator. Birds often eavesdrop on the sirens of other birds to avoid danger, even though they don’t fully understand these “foreign languages” and don’t see their predators.

“Every native bird species we studied responds to the sirens of other species, and we suspect that this behavior is universal across the globe,” Magrath said. “Perhaps this is not surprising, since nearly all species are Predators are a threat, so any clues that can spot predators around you should be used whenever possible.

In a 2019 study, scientists studied eastern gray squirrels found in parks and residential areas in Ohio. They monitored the squirrels’ responses to a perceived threat—the call of a red-tailed hawk—and then to natural responses. Response to birdsong or ambient noise. After monitoring the behavior of each squirrel for 3 minutes, the researchers found that if they heard the soothing sounds of the songbirds, they spent much less time than usual staring up, looking up or running away.

In addition to being used to ensure safety and guard against danger, listening can sometimes prevent animals from starving. In the rainforests of Panama, more than a dozen species rely on almond trees as their main food source. Animals on the forest floor, however, cannot eat the fruit until it falls, or is thrown under a tree by monkeys. Biologists from the Danish Museum of Natural History spent nine months in the rainforest of an island in the Panama Canal, observing raccoons (raccoon-like mammals), agouti (huge but cute rodents) and other scavengers feeding patterns – they usually only take a few bites before throwing the food away. The researchers fitted dozens of animals with GPS collars to track them; they also placed speakers in trees to play monkey sounds, and cameras in trees to record any raccoons and agouti that passed by.

Their findings, published in the journal Biotropics in 2021, show that these ground animals listen to capuchins and spider monkeys to figure out when and where they are feeding. However, as monkeys increasingly leave their local environments (often due to hunting and deforestation), the entire ecosystem’s food chain may soon be at risk. Rasmus Haffmuller, a postdoctoral researcher at the Natural History Museum of Denmark and a co-author of the study, said in a press release that the findings demonstrate how closely connected the animal kingdom is: “The eavesdropping between species makes us more Understand that the loss of one species can have a big impact on the entire ecosystem.”