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Page last updated at 11:49 GMT, Tuesday, 1 December 2009
Clever ravens cooperatively hunt
By Matt Walker
Editor, Earth News

Brown-necked raven (Corvus rufficollis)
Planning the next attack?

Brown-necked ravens team up to hunt lizards, revealing an unexpected level of intelligence, say scientists.

Ornithologists observed a number of birds acting together to trap and kill their prey in Israel's Arava Valley.

Two of the ravens would fly to the ground to block the lizard's escape route, while the others attacked it.

The behaviour suggests the birds must know what each other and the lizard are thinking, known as a 'theory of mind', say the scientists.

Details of the behaviour are published in the Journal of Ethology.

This is a live hunting expedition with the roles spelt out in advance. It is almost like an infantry assault
Professor Reuven Yosef
International Birding and Research Centre, Eilat, Israel

Professor Reuven Yosef of the International Birding and Research Centre in Eilat, Israel and his daughter Ms Nufar Yosef, a doctoral student at Tel Aviv University in Ramit Aviv, observed brown-necked ravens (Corvus rufficollis) hunting a large species of lizard called an Egyptian Mastigure (Uromastyx aegyptius).

During more than 60 hours observing the birds, they watched nine separate hunts take place at two locations.

In each hunt, a number of individual ravens, or pairs of birds, could be seen. But the birds did not flock together.

However, when they sighted a lizard, the teamwork began.

The birds would wait until the lizard had moved away from its burrow entrance.

Then two birds circling overhead would fly in at high speed, landing at the burrow entrance.

This effectively cut off the lizard's escape.

The remaining ravens then targeted the lizard, pecking at it until they had killed their prey, before tearing off pieces to eat.

Only when the lizard was evidently dead did the two ravens guarding the burrow entrance leave their post, and join in to feed.

Egyptian Mastigure (Uromastyx aegyptius)
Egyptian Mastigures make a formidable foe

"This is a live hunting expedition with the roles spelt out in advance. It is almost like an infantry assault," says Prof Yosef.

The ravens succeeded in killing their prey on seven out of the nine hunts.

Outwitting prey

He and his daughter, a psychologist, believe that the cooperative hunt suggests that brown-necked ravens posses what scientists call a 'theory of mind'.

Initially, each raven must recognise that the lizard, which averages 75cm long and can weigh up to 1kg, is too big to take on alone. The reptile also possesses a heavy spiked tail that can easily injure a bird.

Then for each bird to take part in the hunt, and fulfil a particular role, they must have some understanding of what each other is thinking, and be able to realise that by cooperating, they will share in the reward.

To outwit the lizard, they must also have an understanding of how it will likely react.

Other birds, including falcons, shrikes and Harris hawks, are known to hunt in pairs, with one bird flushing out prey into the path of another.

Such hunts are usually performed by breeding pairs or related birds.

But the ravens do not appear to be related, and seem more tactically astute.

Extraordinary feats

Corvids, the group of birds to which brown-necked ravens belong, have astonished scientists with extraordinary feats of memory, an ability to employ complex social reasoning and, perhaps most strikingly, a remarkable aptitude for crafting and using tools.

Last year, a German team of scientists revealed that magpies could pass the Gallup mark test, an indication of whether they are aware of themselves.

Can a magpie pass the mirror test? (footage: Plos Biology)

During the test, magpies marked with a coloured sticker under their beaks tried to remove it when presented with a mirror.

So far, only some species of primates have consistently passed this self-recognition test, although more recent studies suggest elephants and dolphins may also respond.

Corvids' tool-use may also rival, and even surpass, that of primates, such as chimpanzees.

Wild New Caledonian crows craft tools to help them secure hard-to-reach food, for example.

Western scrub jays intentionally deceive each other about the location of food stashes, while last year researchers discovered that rooks will team up to solve problems set for them in experiments.

Earlier this year, scientists even showed that rooks will repeat one of Aesop's fables, by using stones in an experiment to raise the water level in a pitcher so it can reach the liquid to quench its thirst.

Brown-necked ravens are a little studied species which breeds across north and central Africa to southwest and central Asia.

It has been able to expand its range in part due to its ability to exploit human settlements built in desert regions.

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