WASHINGTON - Birds, deer, monkeys and other wild animals all bark — but why are dogs more vocal than others?

The reason is related to dogs’ 10,000-year history of hanging around human food refuse dumps, says evolutionary biologist Kathryn Lord, University of Massachusetts (U-M).

Lord and co-authors also provide scientific literature with its first consistent, functional and acoustically precise definition of this common animal sound.

We suggest an alternative hypothesis to one that many biologists seem to accept lately, which seeks to explain dog barking in human-centric terms and define it as an internally motivated vocalization strategy,” explains Lord who led the study.

In the researchers’ view, however, barking is not a special form of communication between dogs and humans. What we’re saying is that the domestic dog does not have an intentional message in mind, such as, ‘I want to play’ or ‘the house is on fire,’ said Lord.

Rather, she and colleagues say barking is the auditory signal associated with an evolved behaviour known as mobbing, a cooperative anti-predator response usually initiated by one individual who notices an approaching intruder.

A dog barks because it feels an internal conflict; an urge to run plus a strong urge to stand its ground and defend pups, for example. When the group joins in, the barks intimidate the intruder, who often flees.

We think dogs bark due to this internal conflict and mobbing behaviour, but domestic dogs bark more because they are put, and put themselves into, conflicting situations more often, she says.

The reason traces back to the first dogs that started hanging around human food dumps about 8,000 to 10,000 years ago.

They would have experienced a serious disadvantage if they had run a mile away every time a human or other animal approached.

In evolutionary terms, dogs self-selected the behaviour of sticking around, overcoming their fear and being rewarded by getting to eat that meal before some other dog got it,” Lord said.

“Thus these animals allow people to get unusually close. The scared ones die while those less scared stay, eat, survive and reproduce. So they inherit the tendency.

These findings were published in a special issue of Behavioural Processes.