Birds 'can behave like soldiers'

[AndrewA]

Like soldiers in combat zones, birds operate a sentry system to ensure their comrades are safe from attack.

By singing a "watchman's song", the pied babbler tells its group mates they are free to forage for food in Africa's Kalahari desert.

This is a rare example of truly altruistic bird behaviour, said Dr Andy Radford, of Bristol University, UK.

"The unselfish behaviour of the sentry is probably rewarded down the line. It's a win-win scenario," he said.

Pied babblers live in groups of around six or seven, one of whom acts as a sentinel, scanning the desert for predators, such as mongoose, eagles, or even cobras.

Just as soldiers on sentry duty in hostile territory keep in regular radio contact with their colleagues, the sentinel sings a distinctive watchman's song to assure them that all is well.

This leaves the rest of the group free to focus on finding food, such as scorpions and small snakes buried beneath the surface of the sand.

Whistle and weigh

Dr Radford's team observed a study population of 12-20 groups living in the Kalahari, southern Africa.

They demonstrated that the watchman's song allowed groups to capture more food.

Dr Radford said: "These exciting results point to a great example of true cooperation.

"The unselfish behaviour of the sentry is probably rewarded down the line by the improved survival of group mates, which leads to a larger group size.

"This increases the sentinel's chances of survival when the group is under attack from predators or having to repel rivals from their territory."

Though they live in the wild, the groups of pied babblers in the study have been trained to fly in to the researchers in response to a whistle and weigh themselves on a small set of scales.

Observers can then walk within a few feet of the birds to observe their behaviour and monitor the prey that they catch.

Their latest research showed that the foragers respond to the watchman's song alone, whether or not they see a sentinel sitting in a tree.

Language use

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In response to playbacks of recordings of the call, the foraging individuals spent less time looking out for predators, looked up less often, spread out more widely, and spent more time out in the open.

This means that they have more time for foraging, are less likely to lose track of prey, have more foraging patches to choose from and are less likely to encounter patches that have already been depleted.

As a consequence of these changes in behaviour, the birds had greater foraging success.

The research, funded by the Biotechnology and Biological Sciences Research Council (BBSRC), is published in Current Biology.

"Decision making in response to vocal cues is an important behaviour in social birds, and by studying it we can discover much about the way that different groups of animals develop language use," said Dr Radford, a BBSRC David Phillips Fellow.

"We are now investigating whether sentinels differ in their reliability and how this might influence the behaviour of their group-mates."