From whistles to warbles and howls to growls, sound is important for many animals’ survival. Animals call to one another to recognize and locate family members, to find mates, and to warn each other of danger. They might cry out to ward off predators or intruders entering their territory. “Fish, frogs, birds, reptiles, mammals, and even some insects all use sound to communicate,” says Rice. “It’s almost a universal component of life.”

Some animals rely on sound to locate prey and explore the world around them. Bats, dolphins, and whales do this using echolocation. They emit sounds that reflect off objects and back to the animals. This helps them detect an object’s shape, size, and location.  

To catalogue the huge variety of animal sounds, scientists have developed portable devices that record on land and in the sea. Rice, for example, uses hydrophones—underwater microphones—to listen for whale calls and study the animals’ movements. A computer program can quickly scan the audio recording, zero in on specific sounds, and turn them into a visual representation, called a spectrogram, that scientists can analyze (see Seeing Sound). “It’s like reading a score for a musical composition versus listening to the entire piece of music,” says Rice.

Studying the sounds of nature is not limited to just listening in on wildlife. Kurt Fristrup is a senior scientist at the National Park Service’s Natural Sounds Program in Colorado. He and his colleagues monitor acoustic environments—all of a given area’s sounds, both natural and unnatural—at locations across the U.S.’s national park system.

At each site, the scientists set up sound-monitoring equipment, as well as mini weather stations. Factors like humidity, wind speed, and air temperature can affect how sound waves propagate, or move through the air (see How Sound Waves Work). They also take into account each place’s geography and ground cover, since different terrain reflects or absorbs sound differently. 

The data helps Fristrup’s group understand the sounds that make up a particular environment. They can also identify undesirable sounds, like those from planes and cars, as well as other types of human-made noise pollution. “Per person, there’s more transportation noise than in the past, and a lot more noise from personal devices, yard equipment, and recreational vehicles,” says Fristrup.

All that noise can affect animals’ behavior. For example, researchers from Boise State University in Idaho found that road noise has a negative impact on birds. The scientists set up speakers that played sounds of rushing traffic in a remote forest. Fewer birds visited the area around the “phantom road” compared with a nearby site. The ones that did visit foraged less. The scientists think that the noise made it hard for the animals to listen for danger, forcing them to spend more time keeping a lookout and less time eating. 

Understanding how noise drowns out nature is just one way scientists are helping wildlife. Studying sound in the wild can also help scientists monitor threatened animal populations.

Rice is using the audio data he collects to protect the world’s 500 remaining North Atlantic right whales, which live off the east coast of the U.S. His group has installed a series of high-tech buoys in the waters near Boston, Massachusetts. The devices constantly listen for whale calls and alert scientists when a whale is in the area. This information is made available to ship captains so they can take precautions to avoid a collision with the large marine animals.

A similar approach is being used to help forest elephants, which experience some of the highest rates of poaching in the world. People illegally hunt the animals for their ivory tusks. Using sound recordings, scientists are tracking where elephants gather as places to target anti-poaching efforts. “A lot of the work we do takes on a very urgent context when it comes to conservation,” says Rice.