Adult American crows are completely black birds weighing on average 450 g. The feathers have a glossy and slightly iridescent look. Crows have strong legs and toes. The bill is also black with a slight hook on the end. Stiff bristles cover their nostrils. About 20% of male birds are slightly larger than the females.
Young crows are about the same size as adults, but have blue eyes and pink inside the mouth. Both the eyes and mouth darken as the bird becomes an adult. In young birds, the ends of tail feathers are symmetrical and are more pointed than the wide, flat-ended feathers of adults. The wing and tail feathers of the young can become quite brown and ragged through the first winter and spring and only become darker and more glossy like adult feathers after the first molt.
American crows are often confused with common ravens. American crows can be distinguished from common ravens (Corvus corax) most easily by size (ravens are much larger), by voice (ravens are hoarser), by the bill (ravens have heavier, "roman-nosed" bills), and by the shape of the wings and tails, which come to a point in ravens but not crows.
American crows are native to the Nearctic region all over North America. They can be found in the lower part of Canada and through the continental United States.
American crows prefer open areas with nearby trees. Agricultural and grassland areas are ideal habitat for crows to forage for their food. American crows will also use nearby woodlots and forest edges for breeding and roosting. American crows thrive in suburban neighborhoods and urban parks, as well as in coastal habitats.
The oldest recorded age of a wild American crow is 14 years and 7 months.
American crows have an unusual social system - they are cooperative breeders. This means that they may stay close to the place where they were born to help raise young and defend the area against predators. It is not well understood why these offspring do not obtain mates and raise their own families, but pairs with such helpers do not appear to be more successful at fledging offspring than those without helpers. Family members often preen each other (allopreening).
Most American crows defend large all-purpose territories. All members of the family assist in chasing predators away from the territory. Some individuals may remain on their territories during the winter, even if they participate in winter roosts or large flocks searching for food. Winter roosting behavior begins in autumn and peaks in mid-winter. Large numbers of crows, from tens to hundreds of thousands, will assemble in the late afternoon hours in an area with large trees. Often the flock will move from this area to a final roosting area at nightfall.
Some American crows migrate. Researchers have found marked crows from southeastern Michigan as far south as Tennessee, but more often migrants go shorter distances.
In addition to family groups and winter roosts, crows may join a third kind of social group called a floater flock. During the breeding season, floater flocks of up to 50 birds have been observed. Flock participants probably lack mates; at least some of these individuals also spend time on their natal territories as helpers. American crow floater flocks have not been well studied but in other species they allow individuals to roam an area finding mates or vacant territories while staying safely in a group.
American crows engage in a fascinating behavior called anting. A crow will position itself over an anthill and allow ants to scramble among its feathers, or it may pick up an ant and smear its feathers with it.
American crows are considered among the most intelligent birds, though there is little scientific evidence to prove this. American crows are resourceful in their food habits and are extremely difficult for researchers to capture in traps.
American Crows are highly vocal birds. Unlike most other songbirds, males and females have the same songs. They have a complex system of loud, harsh caws that are often uttered in repetitive rhythmic series. Shorter and sharper caws called "kos" are probably alarm or alert calls. Slightly longer caws are probably used in territorial defense, and patterns of repetition may be matched in what may be considered "countersinging," or exchanges between territorial neighbors. "Double caws," short caws repeated in stereotyped doublets, may serve as a call-to-arms vocalization, alerting family members to territorial intruders. Sometimes pairs or family members coordinate their cawing in a duet or chorus. Harsher cawing is used while mobbing potential predators.
People are less familiar with the large variety of softer calls crows can make. Melodic, highly variable coos accompanied by bowing postures are used among family members, possibly as greetings or other bonding signals. Coos of cage-mates become similar over time; this vocalization may therefore be the basis of the mimicry ability shown by pet crows. Crows also give several kinds of rattles.
Young crows make gargling sounds that eventually turn into adult vocalizations. Yearling crows also "ramble" or run through long sequences of different patterns and rhythms of cawing.
American crows are omnivores and will eat almost anything. During the breeding season, American crows consume insects and their larvae, worms, fruits, grains, and nuts. They actively hunt and prey on small animals such as frogs, mice, and young rabbits, though they more likely to scavenge carrion such as roadkill. They also are significant nest predators, preying on the eggs and nestlings of smaller songbirds. In the fall and winter they eat more nuts, such as walnuts and acorns. On rare occasions, American crows will eat from bird feeders put out by humans. Crows often take advantage of human garbage.
American crows store food items such as meat and nuts in short-term caches. Caches are hiding places that are scattered around, rather than in one place. They may be in tree crevices or on the ground, where they are often covered with leaves or other material.
Crows forage primarily by walking on the ground and picking up the item, or by walking along tree branches. Foraging is usually done by a few individuals in a small area, but can also occur in groups over a larger area.
Crows will hold a nut under one foot and strike it with the bill to open it. To open a particularly heavy-shelled food item such as a walnut or clam, a crow will fly high with it and drop it on a hard surface.
Crows will group together to vocally harass and chase predators. This behavior is called mobbing.
American crows do not have significant, unique roles in particular ecosystems. They probably serve as seed dispersers as they eat fruit and cache nuts. They scavenge on carcasses which speeds their decomposition.
Large foraging flocks of American crows may impact agriculture, particularly orchards and cornfields. In the United States there once was a bounty on them. People often consider large roosts to be nuisances when they occur in areas with high human activity; there is concern about noise, mess, and disease from feces. American crows can scatter garbage. As nest predators they may negatively impact population of game birds such as ducks.
Although American crows can be harmful to crops, their impact is shown to be less than what it was previously thought to be. Damage to crops is offset by the amount of damage prevented because the crows eat insect pests. Though it is illegal under the Migratory Bird Act, many people have kept young crows as pets and they are known to mimic human speech. American crows are also considered small game, and hunting seasons exist in many states. Typically they are hunted for sport at times when more valuable game birds cannot be hunted.
American crows are thriving, particularly in association with suburban areas. Their numbers may be increasing.
Cynthia Sims Parr (author), Animal Diversity Web.