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.
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.
These initial studies show that growls and barks do carry meaning that other dogs and, in some cases, people can recognize. This complexity comes as a surprise. Of course, our dogs have known all along—just ask Chocolate and Cina. Still, we know very little about the vocal behavior of dogs.
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.
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.