A group of Ravens can have three different names depending on the activity of the group; a constable, an unkindness, or a conspiracy.

A constable of ravens refers historically to the group of ravens that congregated around the Tower of London; they were thought to be 'keeping watch' over the monarchy. Therefore, any time a grouping of these birds seems to be watching or guarding something, the group can be referred as a 'constable.'

They can also be called an unkindness or a conspiracy - likely for similar reasons. If a flock is driving off other predatory or carrion birds, or 'picking on' another species either because it is competition or prey (although they feed largely on already dead animals, they are known to work together to hunt if need be since they are extremely adaptive birds), then these are apt terms.