Washington, July 16 - 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.