A flock of crows is known as a murder - FactzPedia

A flock of crows is known as a murder.

 

Why is a group of crows called a murder?

A flock of crows is known as a murder. If the verdict goes against the defendant, that bird is killed (murdered) by the flock. The basis in fact is probably that occasionally crows will kill a dying crow

who doesn't belong in their territory or much more commonly feed on carcasses of dead crows.

The term "murder" was used to describe a flock of crows as far back as the 15th century, according to the Oxford English Dictionary. (Here’s a spine-chilling version from 1475: "A morther of crowys.") There was a time once in England when it was fashionable to coin words for groups of animals based on their qualities, whether perceived or real. Hence we have a pride of lions, a gaggle of geese, and a murder of crows. 

Lions were thought to be regal beasts, so they got a proud name. Geese were noisy, flocking creatures, so their group name reflects that. Crows were thought to be loud, thieving birds. so their group name reflects those traits.

The OED suggests this is an allusion to “the crow's traditional association with violent death” or “its harsh and raucous cry." If you've ever heard dozens of agitated crows in full cry, it really does sound as if they're yelling bloody murder.

This usage, which apparently died out after the 1400s, was revived in the 20th century. The first modern citation in the OED comes from 1939, but the usage was undoubtedly popularized by its appearance in An Exaltation of Larks (1968), a compendium of "nouns of multitude" by James Lipton.