02 December 2009
Pack hunting ravens
According to the BBC ornithologists in Israel have observed a birds working together to trap and kill their prey.
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).
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. "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.
Professor Yosef and his daughter 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.
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. The ravens on the other hand do not appear to be related, and seem more tactically astute.
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.
Again this is another of those "wow" moments, or at least it is for me