At night, crows return to a common roost where thousands of birds gather, sometimes flying as many as 80 miles back home. Crows are most vulnerable at night, gathered in a large group, and an owl can do a lot of damage. If crows happen upon an owl during the day they'll mob it and drive it out of the area. Speaking of humans, they used to take advantage of crows roosting habits by dynamiting them at night. Some states paid bounties for the dead crows.
Crows form strong pair bonds, and both parents help raise their young, called simps.
The young bird will stay with its parents for a couple of years, and help feed the next nest of simps. Ravens tend to be more solitary, but they're usually seen in pairs and they mate for life. They have also been observed playing, by sliding down icy rocks. Their acrobatics in flight seem to be part of courtship rituals, but may be a playful activity for them. A wonderful book about crows and ravens, The American Crow and the Common Raven by Lawrence Kilham.