Birds “stand sentry” to help other members of their group forage for food, and sing a special song to give warning of danger, researchers say.

The discovery, by scientists at the University of Bristol, adds to increasing evidence of complex cultural patterns and social co-operation which suggests that the insult “bird brain” is entirely misleading.

The research into pied babblers, a social species from the Kalahari desert of southern Africa that lives in groups of about seven, has revealed a rare example of apparently altruistic behaviour, in which individuals put themselves at a temporary disadvantage for the benefit of others.

While the pied babbler community forages for food, such as small snakes and scorpions dug up from the desert, one of them stands guard in a tree.

This sentinel goes hungry as it watches for predators, allowing its group members to concentrate on feeding. To let other babblers know that it is on guard, the sentry sings a “watchman’s song”, and makes alarm calls if a predator is spotted. Their main predators are gabar goshawks, pale chanting goshawks, sparrow-hawks, slender and yellow mongooses, Cape cobras and puff adders.

While the watchman is singing, foraging individuals spread out and spend more time searching for food than looking out for danger. This allows them a wider range of hunting ground. The effects of listening to the song applied even when a recording was played, according to the study published in the journal Current Biology. The birds did not even look up to ensure that they were being watched.

Andy Radford, who led the £300,000 study funded by the Biotechnology and Biological Sciences Research Council, said the findings showed that birds’ social behaviour could be much more complex than once considered. “These exciting results point to a great example of true cooperation,” he said. “The unselfish behaviour of the sentry is probably rewarded by the improved survival of group mates, which leads to a larger group size.”

A sentry is posted about 30 per cent of the time, and Dr Radford said this could be more likely when the babblers were foraging in areas where they were more likely to encounter predators, or at certain times of day.

All members of the group occasionally perform sentry duty, but there is no obvious rota. There is some evidence that birds stand guard after they eat.

The dominant male is the most likely to become the group’s sentinel, which could mean that the behaviour is partly linked to advertising high status and attracting mates. In many animal species, males use handicaps, such as the peacock’s tail, to show off their superior genetic quality.

“These birds may be saying, ‘Look at me, aren’t I great? I can watch over you all while you feed’,” Dr Radford said.

The sentinel system is not unknown among birds, but the pied babblers are among a very few species that advertise when they are on duty. Florida scrub jays and jungle babblers deploy sentries but make calls only at the start and end of their shifts.

Dr Radford said: “We are now investigating whether sentinels differ in their reliability and how this might influence the behaviour of their group mates.”

Who’s a clever boy, then?

— Crows make tools to fish for grubs. They snap off curved twigs, strip them of leaves and jab them into leaf piles, attracting the attention of their prey. When a grub appears, they impale it

— Ravens, like dolphins and apes, like to play. A pair were filmed in Wales taking turns to slide down a snowy bank. They came back the next day

— Vultures in Rhodesia have been seen sitting by minefields, waiting for gazelles to wander into them. The plan backfired when a vulture landed on a mine

— The great skua, from the Antarctic, has been observed joining in with feeding seal pups to steal a drink of milk from their mother

— Alex, an African grey parrot, knew more than 100 words that he used to describe objects, actions and colours. He could also count to six

— Crows in Japan crack nuts by dropping them into the path of oncoming cars at pedestrian crossings. When the lights turn red, the birds swoop to eat

Source: McGill University, Montreal; American Association for the Advancement of Science; Brandeis University, Massachusetts

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