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Deciphering the message in Fido’s bark

By Carolyn Y. Johnson
Globe Staff / August 8, 2009

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To dog owners, their pet’s “arf, arf, arf’’ means “let’s play!’’ To neighbors, it can be annoying noise. But to scientists, barks are an evolutionary puzzle.

Why, they wonder, do dogs bark, and bark, and bark, sometimes seemingly for no reason?

Researchers at the University of Massachusetts at Amherst and Hampshire College have offered a new explanation for the bark: The rigors of modern canine life trigger a primordial behavior that once helped dogs’ ancestors fend off predators.

Animals - including dogs, deer, monkeys, and birds - bark when they feel a conflict, the researchers believe. For example, should an animal run away or defend her young? In the wild, that bark draws the attention - and the barks - of other members of the group, which could scare away the predator. But in domesticated dogs - confined to crates, yards, and houses and beset by passing cars, unfamiliar dogs, and mailmen - such internal conflicts go into overdrive, and so does the barking.

The research, published in the journal Behavioural Processes last month, is the latest volley in an ongoing scientific investigation of barking.

One question researchers are trying to answer is whether dogs are actually saying something, and, if so, what. The reasons for barking might seem like a frivolous research topic. But to scientists, barking should not be overlooked, considering that it is one of the most conspicuous behaviors displayed by an animal that lives in 40 percent of US households and is often treated like a member of the family.

“They are occupying such an important role in our lives,’’ said Clive Wynne, who studies dogs at the University of Florida and edits the journal that published the article. “If you’re trying to stop a dog barking, it makes a difference if you think it’s barking because it wants to talk to you or because it’s frightened and wants to call your assistance.’’

The scientific debate over dog barking was sparked in part by Hampshire College researchers’ contention in the 1990s that barking served no real function. Domestication, the researchers suggested, made dogs act like adolescents, which could explain their barking because wolves and coyotes bark when they are pups, but rarely as adults.

In last month’s story, researchers reevaluated the work.

It is believed that dogs’ long history with humans began about 10,000 years ago, when they started frequenting human garbage dumps. The ones that were most successful at scavenging food were those that did not run far away when disturbed by an intruder, but stood their ground, putting themselves in bark-inducing situations more often. The dogs that hung around and chowed down at the dump comfortably were probably the ancestors of today’s domesticated dogs, which could have inherited their tendency to not fear contact with intruders.

Their descendants, which live a life with little chance of escape and frequent new stimuli, are bound to bark. Dogs ride in the backs of cars, walk on leashes, and romp around confined yards. Unlike wolves, which keep a distance from novel stimuli, dogs are often subject to intruders, whether a car on the street or the mailman at the door.

“I can’t sniff them. I can’t run away. I’m conflicted!’’ said Kathryn Lord, a doctoral candidate in organismic and evolutionary biology at UMass-Amherst who led the work as part of her dissertation and described the dilemmas dogs might face. “It isn’t that [barking] doesn’t have any function; it actually has an ancestral function.’’

To support the evolutionary argument, researchers also scanned the literature on barking in other animals and found that deer, birds, and monkeys made noises that were similar to barks.

Lord points out that dogs have different kinds of barks and that dogs learn to bark at certain times, finding, for example, that barking gets them food or attention. But she asserts that the widespread belief that dog barks say something specific, like “the house is on fire,’’ is a misconception. Dog barks vary in harshness and pitch automatically, depending on the dog’s internal state, but not to tell humans something in particular.

European researchers have found, however, that people can understand barks. A team based in Hungary played recordings of barks from 19 mudis, a breed of Hungarian herding dog, in different situations. The barks were triggered by such situations as being left alone, playing, and being approached by a stranger. Researchers found that people were able to guess which emotion and situation prompted the bark more often than random chance would suggest.

Lord believes that is not because dogs are intentionally communicating a message, but because all animals vary their calls based on a general set of rules that humans can decode, the way we automatically coo in a high pitch to babies or talk gruffly to a menacing stranger.

Cat lovers should not feel left out of the debate. A study last month in the journal Current Biology examined how purring varied in pitch, depending on whether cats were seeking food.

Scientists found that when cats wanted their owners to feed them, they used a purr that people found more urgent and less pleasant than other purring.

Carolyn Y. Johnson can be reached at cjohnson@globe.com.