I have been scaring dog lovers for nearly a decade, and Tamas Farago—lead researcher behind a new study on dog growls and cross-species communication—is mostly to blame.

I met Farago in 2010 when visiting his research group—the Family Dog Project at Eotvos Lorand University—to conduct my Masters research. By then, Farago was already immersed in the study of dog vocalizations—particularly their barks and growls—so when my study concluded and it was time to leave Budapest, I departed with not only a deep appreciation for paprika and palinka, but also a few audio clips of dogs growling, courtesy of Farago.

Since then, whenever I give a talk about canine science, audience members are sure to chuckle, their faces brightening, as recordings of a dog’s breathy, garbled, fast-paced, play growls take over the room. But when I play the low, elongated aggressive growls corresponding to a dog being approached by a threatening stranger or a dog guarding food, even my hair will often stand up. These growls mean business.  

If a dog happens to be attending the talk—not that I hold lectures for dogs, but if a human brought their dog—I take note before playing the growls. This is because a 2010 study by Farago and colleagues found that dogs not only listen to growls, but extract meaningful information from them. Here’s how they figured this out:

In the study, dogs entered a room where they came across a bone. Fine. Normal so far. Just a bone sitting all alone. But unbeknownst to the dogs, a speaker was concealed in a covered crate sitting just behind the bone, and as the dogs approached, one of three growls was played from the speaker (food guarding, threatening stranger, or play). Excellent work sneaky researchers! The question: how would dogs respond when the different growls were played? Would all growls prompt retreat or a startle response? Or maybe only the two aggressive (agonistic) growls would scare off the approaching dog. Or maybe, just maybe, the food-guarding growl would be most effective in deterring the dog from taking the bone.

I’m not here to pull a 180 on you, so yes, the food-guarding growl reigned supreme. “Play and threatening stranger growls remained ineffective as deterrents, because the subjects probably did not process them as contextually appropriate,” the researchers write. But when dogs heard the “my food” growl, entirely different story; dogs were less likely to take the bone. See for yourself: 

Acoustically, playful growls are in a class of their own: higher-pitched, at least half as short, and faster-pulsing compared to the two agonistic growls, which are longer and lower-pitched. But here’s the kicker: although acoustic analysis found only subtle or no differences between the two aggressive growls, the dogs were able to tell them apart. How on earth? The researchers highlight a subtle difference between the two aggressive growls: “…the dogs always growled at the threatening human with a closed mouth, while during defence of their food they often showed their teeth and pulled back their lips.” Mouth carriage can affect the vocal tract, which in turn could affect sound production.

In their latest publication available open access in Royal Society Open Science, Farago and colleagues found that people, like those I have been mildly scaring in my presentations, can identify growl context better than chance, but not exactly in the same detail as dogs. Listeners correctly classified 81% of play growls, but the food-guarding and threatening-stranger growls “were more difficult to recognize correctly,” explain the researchers. Listeners weren’t totally off the mark on the aggressive growls. People correctly tended to place the aggressive growls within the aggressive or “repellent” category and typically did not mistake them as playful. And listeners did hear differences between the two aggressive growls, rating food-guarding growls as more aggressive while the threatening-stranger growl was rated as more fearful.

Which is good news. If we listen and look, we can hear—and heed—what's in a dog's growl.

References

Faragó, T., Pongrácz, P., Range, F., Virányi, Zs., Miklósi, Á. 2010. ‘The bone is mine’: affective and referential aspects of dog growls. Animal Behaviour, 79: 917-925. (Available here)

Faragó, T., Takács, N., Miklósi, Á., Pongrácz, P. 2017. Dog growls express various contextual and affective content for human listeners. Royal Society Open Science, 170134. http://dx.doi.org/10.1098/rsos.170134

Final paragraph updated 5.25.17 to reflect the differences listeners hear between the aggressive growls.