Hiking yesterday in the hills of Southern California, I saw murders of crows (see below for definition of term) surfing the updrafts and thought about the term “as the crow flies.” Why do we use that term? The crows I saw were circling like hawks. But I remembered seeing crows, hundreds, thousands of them, flying in straight lines over our house, every evening in winter and early spring, always in the same direction, straight as arrows, seemingly from one point to another, as if commuting to work.

American crows commonly sleep overnight in a tree in large dense flocks (they are called murders for some reason) during winter. Sometimes there are thousands of crows packed into just a few trees. This is called communal roosting. Crows fly to the roosts at nightfall. Most large cities have just a few large communal roost sites. Since they have to get to the roost site before dark, crows all across the city all fly in the same direction with their classic steady, purposeful straight-line flight that gave rise to the phrase “as the crow flies.”

There is speculation that hungry crows notice who ate well that day, and the next morning the hungry crows follow the well-fed crows to try to find better feeding sites.