In many bird patterns. Birds of predators were first heard to warn, so the flocks spread out. There is a theory that the birds who screamed saved their companions by attracting attention to themselves, that is, to The self-sacrifice of the birds. The one that most directly undermines these conclusions is:. ["When many flocks of birds inhabit, some birds take turns to act as a vigilant, and scream when they are in danger, in order to increase the group's chance of survival.", 'The shouting bird wants to find a safer place, but dare not search to break the original formation, otherwise the predator will find a single bird out of the formation.', 'When danger comes, the shouting bird may be in a safer position than its companion, it shouts to remind its partner.', 'There is a kinship between the flocks of birds, and there is the same tomb cause among the siblings. Although the shouting bird may sacrifice itself, it can teach more siblings and consequently inherit its genes.']