American crows are capable of breeding after 2 years. Crows nest in February to May in the north and earlier in the south. Mates appear to remain together throughout the year, at least in non-migratory populations, and pair bonds appear to be maintained, even in large winter migratory flocks. Both sexes help build the nest and feed the young. Occasionally, juveniles (nest associates) help with activities associated with nesting. The female incubates the eggs and is fed during incubation by the male and nest associates. Usually 1 brood is produced per year, but there may be 2 broods per pair in southern areas. The average clutch size is 4 to 6 eggs, which hatch in about 18 days. The young fledge about 30 days after hatching and forage with their parents throughout the summer.
Nest success is lowest in populations in urban areas, which averages only 1 fledging per brood. Rural crows have the highest nest success with an average of 1.6 young per brood. Loss of broods may result from a variety of factors including predation by raccoons (Procyon lotor), great horned owls (Bubo virginianus), starvation, and adverse weather.
Nests consist of twigs, sticks, and coarse stems and are lined with shredded bark, feathers, grass, cloth, and string. Usually they are in trees 18 to 60 feet aboveground. Nests are rarely located in deep forests. Where few trees exist, crows may nest on the ground or on the crossbars of telephone poles.
Crows are considered commensal because they thrive in human-impacted environments. Crows rarely breed more than 3 miles from areas habituated by humans. Historically, populations of crows have benefited from agriculture as a source of food and from fire suppression, which allows the growth of trees for roosting.
Crows are among the most intelligent of birds. American crows can count to 3 or 4, are good problem solvers, have good memories, employ a diverse and complex range of vocalizations, and quickly learn to associate specific noises and symbols with food. One report describes an American crow that dropped palm nuts onto a residential street and waited for passing automobiles to crack them. Crows are wary birds, as may be evidenced by the number of crows that scavenge along highways versus how few are seen hit by autos. Juvenile crows are an exception. Crows often post a sentinel while feeding. Studies indicate that the sentinel may be part of a family group, though unrelated crows and other birds in the area likely benefit from the sentinel’s presence.
Research indicates that roosting crows may have 2 distinct, daily patterns of movement. Some fly each day to a diurnal activity center, maintained by 4 or 5 birds. Individuals within the groups typically fly different routes and make different stops. Other crows appear to be unattached and without specific, daily centers of activity or stable groups. The unattached birds, possibly migrants, are not faithful to a specific territory and feed more regularly at sites such as landfills.
Few wild crows live longer than 6 years, but some have lived up to 14 and crows in captivity have lived for over 20 years. One researcher reported a wild crow that lived 29 years. Adult crows have few predators, with the occasional exceptions of large hawks and owls.
One important and spectacular aspect of crow behavior is the congregation into huge flocks in fall and winter (Figure 4). Large flocks are the result of many small flocks gradually assembling as the season progresses, with the largest concentrations occurring in late winter. The Fort Cobb area in Oklahoma has a communal roost that holds several million crows each winter. In several other states, crows commonly roost in towns, resulting in mixed opinions on how to deal with them. Flocks roost together at night and may fly 6 to 12 miles outward from a roost each day to feed.
American crows prefer habitats that include open fields where food can be found, and woodlots with trees for nesting and roosting. They commonly use woodlots, wooded areas along streams and rivers, farmlands, orchards, parks, and suburban areas. American crows select trees for roosting that are larger and have more canopy than other trees in areas with high levels of light at night that are less than 2 miles from sources of food.
Crows are omnivorous. They eat almost anything, and they readily adapt foraging habits to changing seasons and available supplies of food. They appear equally adept at hunting, pirating, and scavenging. Crows consume over 600 different food items.
About ⅓ of the annual diet of crows consists of animal matter, including grasshoppers, beetles, beetle larvae (white grubs, wireworms), caterpillars, spiders, millipedes, dead fish, frogs, salamanders, snakes, eggs, young of birds, and carrion. Garbage is a primary source of food, particularly in urban areas. The remainder of the diet consists of vegetable or plant matter, particularly corn, much of which is obtained from fields after harvest. Crows also consume acorns, wild and cultivated fruits, watermelon, wheat, sorghum, peanuts, and pecans.