Excerpt from The Genius of Dogs: How Dogs Are Smarter Than You Think, by Brian Hare and Vanessa Woods. Published by Dutton, a Member of Penguin Group (USA), Inc. © 2013 Brian Hare and Vanessa Woods. Excerpted with permission from the publisher. All Rights Reserved.
Mystique is a dog who lives at Lola ya Bonobo, [the wildlife sanctuary in the Democratic Republic of the Congo] where Vanessa and I study bonobos. During the day, she is sweet and demure, but at night she becomes a different animal. She guards our house, barking ferociously every time someone comes within earshot. Usually in Congo, a little extra security is appreciated. The only problem is that our house is on the main trail where the night staff walk back and forth after dark. Mystique dutifully barks at all passersby whether she has known them for a day or all her life. Eventually, we just learned to sleep through it. But if there was really a cause for concern, like a strange man with a gun, I wonder if Mystique would bark in a way that would alert me that there was something dangerous and different about the person approaching the house.
Dog vocalizations may not sound very sophisticated. Raymond Coppinger pointed out that most dog vocalizations consist of barking, and that barking seems to occur indiscriminately. Coppinger reported on a dog whose duty was to guard free- ranging livestock. The dog barked continuously for seven hours, even though no other dogs were within miles. If barking is communicative, dogs would not bark when no one could hear them. It seemed to Coppinger that the dog was simply relieving some inner state of arousal. The arousal model is that dogs do not have much control over their barking. They are not taking into account their audience, and their barks carry little information other than the emotional state of the barking dog.
Perhaps barking is another by-product of domestication. Unlike dogs, wolves rarely bark. Barks make up as little as 3 percent of wolf vocalizations. Meanwhile, the experimental foxes in Russia [that have been bred to be docile] bark when they see people, while the control foxes do not. Frequent barking when aroused is probably another consequence of selecting against aggression.
However, more recent research indicates that there might be more to barking than we first thought. Dogs have fairly plastic vocal cords, or a “modifiable vocal tract.” Dogs might be able to subtly alter their voices to produce a wide variety of different sounds that could have different meanings. Dogs might even be altering their voices in ways that are clear to other dogs but not to humans. When scientists have taken spectrograms, or pictures, of dog barks, it turns out that not all barks are the same—even from the same dog. Depending on the context, a dog’s barks can vary in timing, pitch, and amplitude. Perhaps they have different meanings.
I know two Australian dogs, Chocolate and Cina, who love to play fetch on the beach. Each throw sends them plunging through the waves, racing for that magic orb of rubber. When Chocolate retrieves the ball, inevitably Cina wrestles the ball from Chocolate’s mouth, even while Chocolate growls loudly. The girls also eat together, but when Cina tries the same trick with Chocolate’s food, the result is very different. A quiet growl from Chocolate warns Cina away.
It is difficult to see how Cina knows when it is okay to take something from Chocolate’s mouth, since both growls are made when Chocolate is aggravated and unwilling to share. If anything, Chocolate’s growl seems louder and scarier when she is playing than when she is eating.
Experiments have now shown that dogs use different barks and growls to communicate different things. In one experiment, researchers recorded a “food growl” where a dog was growling over food, and a “stranger growl” where a dog was growling at the approach of a stranger. The researchers played these different growls to a dog who was approaching a juicy bone. The dogs were more hesitant to approach if they heard the food growl rather than the stranger growl.