 American crows are very social birds forming small family groups which occupy their own territories. They stay in these groups during the day, especially while foraging. But after the breeding season, some leave each evening to form large communal roosts. Crows will leave their territories in mid-afternoon and arrive at roosts an hour before sunset. Flying in by the hundreds, these roosts often swell with tens of thousands of birds present. So keep an eye to the sky on your evening commute and see if you can spot a murder of crows heading to their roost.