It's an eerie sight – every winter, around dusk each night, a flock of between 20,000 and 30,000 crows gathers in the trees around the Black River in Watertown. They can be a neat sight against the white winter landscape, but the city wants them gone. That's because they squawk and poop and generally annoy a lot of city residents. The city has hired a wildlife management company to disperse the birds.