The Social Lives of Crows
by Brian Kraskiewicz, Natural Resources
Mobbing, holding a grudge, funerals, murders. They may sound like popular themes for a crime story, but they’re also a few of the behaviors of the American crow.
American crows are common sights in DuPage forest preserves and backyards. Most people know these large black birds for their diverse diet (nuts, fruits, seeds, insects, bird eggs, small mammals, garbage, carrion) and their distinctive “caw, caw” vocalizations, but many may not know that researchers study crows for their complex social behaviors and intelligence.
Crows are social animals that often live in extended family groups. Young will stay with their parents for up to two years as “helpers” to aid in building nests and rearing and protecting new chicks. As older birds, crows gather in large groups, hanging out at night in roosts containing one or two dozen to thousands of individuals and dispersing during the day to forage for food.
This communal social system is especially seen in crows’ mobbing behavior, a defensive strategy the birds use when a predator is nearby. If a crow discovers a hawk, owl, or other danger in its territory, it will start to harshly caw. This alarm attracts other crows, who join in the calling. (If you ever hear a group of crows cawing like this, be on the lookout for a bird of prey!) Some may even dive bomb the intruder. This effective behavior usually causes the predator to move on.
Crows are also known to carry — and pass on — grudges. In one study, researchers from the University of Washington wore caveman masks and then captured, marked, and released several crows. They then took turns wearing the mask around campus, noting the birds’ responses. Crows that were captured cawed at the person wearing the mask but ignored other people and even other masks. But the crows that were never captured seemed to quickly learn that the caveman mask represented danger as they, too, began to scold and target the person wearing it. The researchers concluded that the captured crows not only held grudges against the person in the caveman mask but also taught other crows that the mask was a danger to avoid.
One of the more interesting behaviors of crows, which is not common in the animal world, is a funeral or wake for a deceased member of the group. Researchers, again from the University of Washington, placed a taxidermied crow outdoors. When a crow discovered the deceased, it would call out, alerting others. As other crows gathered, the group continued to make noise. The researchers theorized that the crows were sending a call out to look for nearby predators or other threats that may have caused the death. The study also revealed that if a predator or human was in the area when the crows gathered, they would scold that individual — even weeks later.