In many bird samples, it is first discovered that the predator's bird makes a warning call
When many bird flocks roost, some birds will take turns to act as a guard, and make calls when they are in danger, thereby increasing the flock's chances of survival
the flock of birds disperses. There is a theory that the calling bird saves its companion by attracting attention to itself, that is, to Self-sacrifice for the benefit of the flock.