Dogs can know what other canines mean when they growl- right from a rumble that says "back off" to playful snarls made in a tug-of-war game.

In 2008, Peter Pongracz, a behavioural biologist at Eotvos Lorand University in Budapest, Hungary, monitored dogs' heart rates to show that they seem to notice differences between barks aimed at strangers and those directed at nothing in particular.

And in the new study, he has gone a step further and shown that dogs respond differently to different vocalisations.

The researchers recorded growls from 20 pet dogs in three different situations: a tug-of-war game with their owner, competing with another dog for a bone and growling at an approaching stranger.

Pongracz said that growls may convey more meaning than barks- wolves rarely bark, and he says dogs may have learned to bark to get human attention.

The team played the recordings to 36 other dogs that had each been left to gnaw on a bone. Only those that heard the food-guarding growls tended to back off from the bone and stay away.

"It seems dogs can understand something about the context," New Scientist quoted Pongracz as saying.

Just two of the 12 dogs that heard the stranger growl and four of the 12 that heard the tug-of-war growl withdrew.

All dogs but one in each of these groups eventually returned to their bone.

"Dogs' growls seem to have distinct meanings. I think it is fair to say that they are used intentionally," said Alexandra Horowitz at Barnard College in New York.

Growls also offer a good indicator of size.

The study has been published in the journal Animal Behaviour. (ANI)