London: Animals are known to sound alarm calls when predators are around, particularly when their kin are present, reveals a study.

But when chimps spot a snake, they are likely to warn groups unaware of the danger, suggesting that they recognize knowledge and ignorance in others, say researchers from the Planck Institute for Evolutionary Anthropology, Germany, and University of St. Andrews, UK.

'Chimpanzees really seem to take another's knowledge state into account and voluntarily produce a warning call to inform the others of a danger that they (others) do not know about', said researcher Roman Wittig from Max Planck. Conversely, 'chimpanzees are less likely to inform audience members who already know about the danger'.

This study thus suggests that this stage was already present when our common ancestor split off from chimps six million years ago. The ability to recognize another individuals' knowledge and beliefs may be unique to humankind, a university statement said.

'The advantage of addressing these questions in wild chimpanzees is that they are simply doing what they always do in an ecologically relevant setting,' said Catherine Crockford, researcher at the University of St. Andrews.

Crockford and Wittig along with colleagues set up a study with wild chimps in Budongo Forest, Uganda. They presented them with models of dangerous venomous snakes, two gaboon vipers and one rhinoceros viper.

'As these highly camouflaged snakes sit in one place for weeks, it pays for the chimp who discovers it to inform other community members about the danger,' said Crockford.

The researchers monitored the behaviour of a group of different chimps, who saw one of three snake models and found that alarm calls were produced more when the caller was with group members who had either not seen the snake or had not been present when alarm calls were emitted.