Video: When dogs talk

Budapest, Hungary

-- According to the results of an animal-behavior study on growls, food guarding is the most clearly understood cue in the canine world.

Published in early 2010 by Tamas Farago, Peter Pongracz, Friederike Range, Zsofia Viranyi and Adam Miklosi, "The bone is mine: Affective and referential aspects of dog growls," investigated canine communication in three situations -- a threatening social conflict, when guarding food and during social play.

To begin, researchers recorded the growls of 20 adult dogs of varying ages, sizes, breeds and sexes. To simulate a threatening situation, a dog’s owner held the leash while a stranger slowly, silently approached and continually stared at the dog. To elicit a playful growl, the dog and its owner played a game of tug-of-war. The final experiment involved food. A dog was given a large, meaty bone. When it started to chew on the bone, another unfamiliar dog was led out and approached the chewing dog.

Each session ended when approximately 10 growls were recorded.

But could a dog understand and then react to another dog’s growl?

Once the growls were processed, 41 dogs -- at least 1 year old and of different breeds, sizes and sexes -- were recruited to listen to the growls. Five of the initial dogs were excluded after showing no interest in a bone.

With a speaker system hidden in a covered dog cage and a fresh, cooked bone on the floor, a dog and its owner entered the test room. The owner, who was not allowed to touch, talk or look at the dog, led the dog around the room, allowing it to sniff at the bone from about eight inches away. The owner then led the dog about 10 feet away and, on a signal from the researchers, released the dog.

When the dog got within two inches of the bone, the experimenter (in a different room) played a growl sequence. If the dog left the bone or if the dog did not approach the bone again within the next 90 seconds, the experiment was over. If the dog approached the bone again, the sequence of growls was played again. If the dog did not leave the bone, the sequence was played a maximum of three times. If the dog was still chewing, the test was stopped.

The researchers watched how frequently the dog made contact with the bone or left it, and the duration -- licking, chewing, and taking the bone away from its original location -- of the encounter.

After hearing the growl for the first time, 11 out of 12 dogs in the food-guarding growl group withdrew from the bone within 15 seconds. Only two of the 12 dogs from the threatening-growl group, and four of the 12 dogs in the play-growl group withdrew in the same time frame.

Seven dogs from the food-guarding growl group did not approach the bone again within the next 90 seconds. However, only one dog in each of the threatening-growl and play-growl groups stayed permanently away from the bone.

The researchers found that the food-guarding growls were a stronger deterrent to the dogs than the threatening-growls. Most of the dogs in the food-guarding growl group left the bone and only one ate it. But in the threatening-growl group, most of the dogs took the bone away or ate it. They also found that more dogs in the play-growl group left the bone than in the threatening-growl group, causing them to conclude that these growls evoked ambivalent responses from the dogs.

However, not knowing exactly what a dog is "feeling" during a specific situation could explain why play growls and threatening growls remained ineffective as deterrents. The test subjects probably did not process them as contextually appropriate, the researchers say.

The dogs in the food-guarding growl group took longer to approach the bone than dogs in the other two groups.And the theory that the bigger the dog, the bigger and scarier its growl was not supported either. The researchers found that a dog’s size, and its accompanying growl, had no major impact on the experiment.

The researchers also studied the acoustic quality of the growls, but admitted the sample was not suitable for a detailed acoustical analysis. In this study, they found no significant acoustic difference between food-guarding growls and threatening growls.

They did, however, find a large difference between play growls and the food-guarding and threatening growls. Play growls were at least half as short, as well as higher pitched than the other two growls. The researchers suggest future studies look at the subtle acoustic differences between similar growls, like the food-guarding and the threatening growls.

For now, it seems, dogs are extremely capable of deciphering another dog’s growl when it comes to a big, juicy bone. Read the full report in the April edition of Animal Behavior.

Replay the three growl types below:

Playful growl

Threatening growl

Food-guarding growl