American Crows are highly social birds, more often seen in groups than alone. In addition to roosting and foraging in numbers, crows often stay together in year-round family groups that consist of the breeding pair and offspring from the past two years. The whole family cooperates to raise young. Winter roosts of American Crows sometimes number in the hundreds of thousands. Often admired for their intelligence, American Crows can work together, devise solutions to problems, and recognize unusual sources of food. Some people regard this resourcefulness and sociality as an annoyance when it leads to large flocks around dumpsters, landfills, and roosting sites; others are fascinated by it. American Crows work together to harass or drive off predators, a behavior known as mobbing.