If one chicken in the flock gets a sore the other chickens will peck at the sore until the chicken with the sore dies.
I’ve seen crows exhibit similar behavior - not necessarily in response to sores, per se; but they will go against another crow who has apparently done something socially ‘incorrect’, or exhibited weakness; or is a foreigner who has wandered into their territory without ‘fitting in’.
The cries of the accused one being assaulted in this way are pitiful.
I have always loved birds; but they can be very ‘vicious’ by civilized human lights.