What’s in a Howl?

The howl of a wolf sparked dread in medieval Europeans and American settlers, and it still inspires fear in ranchers worried about their livestock. For biologists, the sound signals a major conservation victory — the return of a North American apex predator and its restorative impact on the food chain and landscape. But what about the intended recipients of the howl? What information do wolves receive through those long-range vocalizations? In short, what’s the meaning of a howl?

Despite our centuries-old fascination, we have few answers. Observing wolves in natural settings is extremely difficult, and experiments on captive wolves have only limited value because those animals don’t display the same social behaviors as their wild brethren. But scientists think they might be on their way to a breakthrough. After analyzing thousands of recordings of wolves, coyotes and other canids, they’ve identified distinct types of howls and created howl profiles for each species and subspecies. Now they are recording and observing the wolves of Yellowstone National Park and hope to match the different howl types with the activities of the animals to figure out what they are saying.

“You don’t want to overstate your claim,” said Sara Waller, a Montana State University philosophy professor coordinating the Yellowstone study, “but it would be very exciting if one day we could all take Wolf 101 and talk to the animals like Dr. Dolittle.”

Wolves make other sounds — they bark, growl and yip — but howls are the only ones that travel long distances. They are meant to be heard up to 6 miles away in forested land so they have to convey information without relying on body language. The two primary functions of howls are to indicate the boundaries of the wolves’ territory to rivals and to keep track of family members, said Doug Smith, leader of the Wolf Restoration Project in Yellowstone. “So one howl is ‘stay out,’ and the other howl is ‘where are you?’” he said.

Anecdotal evidence also suggests wolves use howls to convey emotions. The late wolf biologist Gordon Haber observed wolves howling in “obvious pain and distress” when they were caught in a trap or a snare. Smith said that he’s also seen wolves that have lost a mate howl “for a lack of a better way to put it, mournfully.”

Smith also said howling varies according to seasons. Its frequency goes down in the spring and early summer because wolves don’t want other packs to identify the location of their den and potentially kill their pups, he said. And it gradually increases again toward late summer as pups grow less vulnerable.

Fred Harrington, a wolf howl expert at Mount Saint Vincent University in Canada, said howls can be aggressive or lonesome and can also vary depending on which other pack members are around. Harrington said that pups howl differently depending on whether they are with adults or by themselves, for instance. What’s more, the same howl can be interpreted differently. During his research in northern Minnesota, Harrington howled at wolves to trigger responses, which is a standard practice in wolf research (he said a fellow researcher who lacked confidence in his howling ability used a siren with similar results). Although wolves usually retreated, some would instead move closer, apparently intrigued.

But before you can interpret howls, you have to figure out the different kinds that exist. Arik Kershenbaum, a biologist with the University of Cambridge, and six others — including Sara Waller — used a computer algorithm to identify 21 different howl types based on their frequency modulation. They then looked at how often the animals used each howl type — red wolves and coyotes, for instance, produce all 21 howls, but arctic wolves use only nine — and compiled that information to establish howl profiles for 13 different canine species, including gray wolves like those in Yellowstone and domestic dogs.

This work, which was recently published in the journal Behavioural Processes, could yield important conservation benefits. Red wolves are listed as an endangered species in the United States even as scientists debate their taxonomic status. Some consider them hybrids between gray wolves and coyotes, while others view them as a separate species at risk of disappearing through interbreeding with coyotes. Kershenbaum said understanding the vocal differences between red wolves and coyotes could help conservationists monitor and manage the two populations.

Distinguishing howl types could also help mitigate conflicts between wolves and farmers. Ranchers sometimes use devices playing wolf howls to keep wolves away, but it’s possible that those recordings have been largely unsuccessful because they have been playing the wrong howl.

“A howl that says ‘everyone, come over here! It’s time to go hunting and catch some food’ is not the kind of thing that you want to be broadcasting around your sheep,” Kershenbaum said.

One of the main challenges in studying wolf howls is that it’s really difficult to identify which animal is howling, because wolves are often obscured by forest cover. This is where the scientists’ current work in Yellowstone could help. Not only do Yellowstone’s clearings offer a direct line of sight to the wolves, but many of the park’s wolves wear radio collars so their location can be tracked. Researchers have set up five recording devices that they move as the packs roam through the park. They plan to use the recordings and park biologists’ detailed observations of what wolves are doing — reuniting after a hunt or rousing from sleep, for example — to move closer to deciphering the howls.

Waller is interested in more than the research’s potential conservation applications. Having studied the philosophy of language, she found that none of the theories seeking to explain how words got their meaning was satisfying. She hopes that the wolves — social animals that rely on cooperation and have strong family bonds — can teach us about the origins of our own language. Waller said using the word “language” to describe wolf communication remains controversial but that the similarities with our own communication patterns are striking.

“My money is on that it’s going to be much closer to human language than we expected,” she said, “but it’s still a bet on my part.”