American Crows operate an early-warning system to protect their gatherings while they forage. They post sentinels and revolve these guards to make sure everyone is fed.
The collective noun for a gathering of these birds is a “murder of crows,” a term that has been attributed to the influence of folk tales. In one tale, the reason that crows gather together is to decide whether to put one of their kin to death for violating a crow rule; in many other tales, crows and ravens are omens of an impending death.
(Brooklin, Maine)