As recently pointed out, hunting in groups is often no more successful than doing it alone. I can't think of any nonhuman examples, except insofar as animals bully each other into giving up food or not breeding. This is always to the advantage of the bully and the disadvantage of the victim - whether it aids the group is irrelevant. At least you haven't got dinosaurs talking and wearing waistcoats. Flocks of birds don't 'send' out detachments.
Individual birds react to the threat.
Parents can pass information on to their offspring. No other adults need be present.