A fairly common sight is bands of American crows chasing and generally harassing owls during the day. That is because great horned owls go into crow roosts at night to take crows for food. The voices of the crows carry the hysterical fear of their night over into the day. Owls, however, will go to the crow roost again and repeat the ritual.

Mobbing is the customary response of birds to certain predators that pose a threat, whether that predator is a cat, fox or large snake. The behavior is a survival strategy, the crows 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. I have seen chickadees and other small birds engaged in this activity against small owl species. Crows must spend a good part of their day finding and eating food, and they eventually lose interest in the owl. Then the mobbing response subsides.

In the southern half of Minnesota, American crows are seen regularly in winter. Crows are stocky black birds that weigh about a pound and have a wingspread of about 3 feet. They gather in communal roosts of hundreds or even thousands in fall and winter. They disperse every morning in small groups to feed and then return.

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.