American crows, those stock, black birds with 3-feet wingspans, have a spectacular winter habit: their nightly communal roosts.

The roosts can reach upward of 50 birds — but even as many as thousands of individuals. Watch the direction in which groups of crows are flying in the late afternoon or coming from in early morning — there’s probably a roost in that direction.

One of the most adaptable birds, American crows live over almost the entire United States. Small flocks may travel up to 50 miles each day to eat. The omnivores will go after remaining corn in harvested fields; other grains; weed seeds; wild fruits; many insects; spiders; snakes; animal matter collected near water; roadkill, and our garbage. We could call them nature’s cleaner-uppers.

Since great horned owls go into crow roosts at night to take crows for food, we often see bands of crows chasing and harassing owls during the day. I have observed this many times, and will never forget the voices of the crows carrying the hysterical fear of their nights over into the days.

Mobbing is the customary response of birds to certain predators, such as cats and foxes, that pose a threat. No doubt this behavior has survival value to the mob by drawing attention to the whereabouts of a killer. When owls are discovered, the action that best ensures survival of the local birds seems to be exposing the enemy by mass display or mobbing. Even chickadees and other small birds engage in this activity against small owl species. Because crows must spend a good share of their day finding and eating food, they eventually lose interest in the owl, and the mobbing response ends.

Jim Gilbert’s Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays. His observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.