In the Rooky Wood

Great Horned Owl vs. Crow, photo by Jerry DeBoer

It seems like everyone hate crows. Throughout much of the world, crows--ravens, carrion crows, jackdaws, rooks, choughs--fill the same niche as vultures. Garbage collectors are indispensable of course, but not celebrated. Associated with death and bad fortune in European folklore, crows have been an object of persecution. 
Then there's that voice. I once worked with a nun who had some very uncharitable things to say about crows. She complained that they perched at the top of the chapel's cross and screamed! And they did. 
After Macbeth murdered his king, he plans more killings with these lines (3.2.50-53):

Light thickens, and the crow

Makes wing to the rooky wood:

Good things of day begin to droop and drowse;

While night's black agents to their preys do rouse.

(Of course, crows and rooks are not nocturnal, but this is Shakespeare, not ornithology.)
Kevin McGowan has been studying crows for 20+ years, and his research shows that those groups we see as feathered juvenile delinquents are actually families. Just as we wouldn't tolerate a dangerous snake or spider in our home, crows vigorously defend their nesting area against predators. In winter, when crows gather at night in roosts, sometimes in the hundreds or thousands, what could be more terrifying than an owl swooping through the dark to take a one as prey? No wonder crows take every opportunity to drive owls away. Studies show that American Crows are at or near the top of the intelligence quotient of all birds, and those calls, which seem so offensive, have variety and meaning.

Birders know that a flock of screaming crows often means that an owl is nearby. Sometimes the owl will flee its tormentors, sometimes--as in the amazing photo above, by Jerry DeBoer--they stay put, stoic and grumpy.  Why doesn't the owl attack? Great Horned Owls are the top bird predator in our region, with a wing span up to 5 feet. For a bird, it's quite heavy: around 3 pounds--triple the weight of an American Crow. Beyond the fact that owls are most adept at maneuvering in the dark and crows have some advantage in daylight, the answer to that question remains a mystery.