Crow

Wildlife Damage Management June 18, 2013|Print

Crow | Crow Overview | Crow Damage Assessment | Crow Damage Management | Crow Resources | Crow Acknowledgments | ICWDM | Wildlife Species Information

 

Image:Crow1.gif

Figure 1. American crow, Corvus brachyrhynchos (also called the common crow or eastern crow)

Identification

The American crow (Fig. 1) is one of America’s best-known birds. Males and females are outwardly alike. Their large size (17 to 21 inches [43 to 53 cm] long), completely coal-black plumage, and familiar “caw caw” sound make them easy to identify. They are fairly common in areas near people, and tales of their wit and intelligence have been noted in many stories.

Three other crows occur in the continental United States, the fish crow (Corvus ossifragus), the northwestern crow (Corvus caurinus), and the Mexican crow (Corvus imparatus). Fish crows are primarily inhabitants of the eastern and southeastern coastal United States, but their range extends into the eastern edges of Oklahoma and Texas. Fish crows are somewhat smaller than American crows, but in the field they appear much alike. They can be distinguished, however, by their calls — the fish crow call is a short, nasal “ca,” “car,” or “ca-ha.” Northwestern crows, as their name implies, occur in the northwest along the coastal strip from Washington to Alaska. They are most often seen foraging along beaches. Northwestern crows are smaller than American crows, but in Washington state these two species may hybridize. Mexican crows occur in south Texas (Brownsville area) primarily during fall and winter and are fairly small for crows. Their voice is a low froglike “gurr” or “croak” or, in some areas, a higher-pitched “creow.”

Ravens are similar to crows in appearance. Two species occur in the continental United States, the common or northern raven (Corvus corax) and Chihuahuan or white-necked raven (Corvus cryptoleucus). The common raven is found from the foothills of the Rockies westward, northward to Alaska and eastward across Canada and some northern U.S. states, and locally in the Appalachian Mountains. Common ravens can be distinguished from crows by their larger size, call, wedge-shaped tail, and flight pattern that commonly includes soaring or gliding. In contrast, crows have a frequent steady wing-beat with little or no gliding.

Chihuahuan ravens occur in the Southwest, including portions of western Kansas, Colorado, Oklahoma, Texas, New Mexico, and Arizona and rarely in south-central Nebraska. This raven, which is smaller than the common raven and somewhat larger than the American crow, can be distinguished from the crow by its call, slightly wedge-shaped tail, and flight pattern that includes gliding. The white neck feathers, which account for its other name, are seldom visible in the field.

General Biology, Reproduction, and Behavior

Crows are among the most intelligent of birds. Experiments indicate that American crows can count to three or four, are good at solving puzzles, have good memories, employ a diverse and behaviorally complex range of vocalizations, and quickly learn to associate various noises and symbols with food. One report describes an American crow that dropped palm nuts (Washingtonia sp.) onto a residential street, and then waited for passing automobiles to crack them. Crows are keen and wary birds. Consider the number of crows that scavenge along high-ways; how many have you seen hit by autos? Crows can mimic sounds made by other birds and animals and have been taught to mimic the human voice. The myth that splitting the tongue allows a crow to talk better, however, is not true and is needlessly cruel.

Crows often post a sentinel while feeding. Although studies indicate that the sentinel may be part of a family group, unrelated crows and other birds in the area likely benefit from the sentinel’s presence.

Crows begin nesting in early spring (February to May, with southern nests starting earlier than northern ones) and build a nest of twigs, sticks, and coarse stems. Crow pairs appear to remain together throughout the year, at least in nonmigratory populations, and pairs or pair bonds are likely maintained even within large winter migratory flocks. The nest, which is lined with shredded bark, feathers, grass, cloth, and string, is usually built 18 to 60 feet (5 to 18 m) above ground in oaks, pines, cottonwoods, or other trees. Where there are few trees, crows may nest on the ground or on the crossbars of telephone poles. The aver-age clutch is 4 to 6 eggs that hatch in about 18 days. Young fledge in about 30 days. Usually there is 1 brood per year, but in some southern areas there may be 2 broods. Both sexes help build the nest and feed the young, and occasionally offspring that are 1 or more years old (nest associates) help with nesting activities. The female incubates the eggs and is fed during incubation by the male and nest associates. The young leave the nest at about 5 weeks of age and forage with their parents throughout the summer. Later in the year, the family may join other groups that in turn may join still larger groups. The larger groups often migrate in late fall or winter.

Few crows in the wild live more than 4 to 6 years, but some have lived to 14 years in the wild and over 20 years in captivity. Recently, a bird bander reported a crow that had lived an incredible 29 years in the wild. Adult crows have few predators, although larger hawks and owls and occasion-ally canids take some. Brood losses result from a variety of factors including predation by raccoons (Procyon lotor), great-horned owls (Bubo virginianus), and other predators; starvation; and adverse weather.

One important and spectacular aspect of crow behavior is their congregation into huge flocks in fall and winter. Large flocks are the result of many small flocks gradually assembling as the season progresses, with the largest concentration occurring in late winter. The Fort Cobb area in Oklahoma, a communal roost site, holds several million crows each winter. In Nebraska, Wisconsin, and possibly other states, crows appear to be roosting more commonly in towns near people, resulting in mixed opinions on how to deal with them. These flocks roost together at night and disperse over large areas to feed during the day. Crows may commonly fly 6 to 12 miles (10 to 20 km) outward from a roost each day to feed.

Recent radio-telemetry studies indicate that roosting crows may have two distinct daily movement patterns. Some fly each day to a stable territory, called a diurnal activity center, which is maintained by four or five birds throughout the winter and apparently then used as a nesting site in spring. Although these stable groups of crows may stop at superabundant food sources such as landfills, individuals within the groups typically fly different routes and make different stops. Other crows appear to be unattached and without specific daily activity centers or stable groups. Although they use the same roosts as the activity-center crows, these unattached birds, possibly migrants, are not faithful to any specific location or territory and more regularly feed at sites such as landfills.

Ongoing changes in land-use patterns may result in associated impacts on crow populations and behavior. Historically, crow populations have benefited from agricultural development because of grains available as a food supply and because trees became established in prairie areas where agriculture and settlement suppressed natural fires. The combination of food and tree availability favored crows, and in some areas with abundant food and available roost sites, large winter roosting concentrations became established. As the current trend toward sustainable agricultural systems continues, which may include a variety of crops and rotations with nongrain crops, food availability and associated patterns of crow roosts may change.

The growing number of crows that nest and roost in urban areas also raises questions. Are urban habitats now selected because of adaptive changes in crow behavior, or are changes in rural settings making urban sites comparably more suitable? One study described two neighboring but distinct crow nesting populations — one that was urban and somewhat habituated to people and another that was rural and relatively wary of people. Will crows that are hatched in urban areas be habituated to people to such an extent that they will be more difficult than their rural counterparts to disperse from problem sites? Understanding such factors may lead to better options for managing crows in ways compatible with the needs of people.


 

Crow | Crow Overview | Crow Damage Assessment | Crow Damage Management | Crow Resources | Crow Acknowledgments | ICWDM | Wildlife Species Information

 

Range

American crows are widely distributed over much of North America. They breed from Newfoundland and Manitoba southward to Florida and Texas, and throughout the West, except in the drier southwestern portions. During fall, crows in the northern parts of their range migrate southward and generally winter south of the Canada-US border.

Habitat

American crows do best in a mixture of open fields where food can be found and woodlots where there are trees for nesting and roosting. They commonly use woodlots, wooded areas along streams and rivers, farmlands, orchards, parks, and suburban areas. Winter roosting concentrations of crows occur in areas that have favorable roost sites and abundant food.

Food Habits

Crows are omnivorous, eating almost anything, and they readily adapt food habits to changing seasons and available food supply. They belong to a select group of birds that appear equally adept at live hunting, pirating, and scavenging. Studies show that crows consume over 600 different food items.

About one-third of the crow’s annual diet consists of animal matter, including grasshoppers, beetles, beetle larvae (white grubs, wireworms), caterpillars, spiders, millipedes, dead fish, frogs, salamanders, snakes, eggs and young of birds, and carrion such as traffic-killed animals. The remainder of the crow’s diet consists of vegetable or plant matter. Corn is the principal food item in this category, much of it obtained from fields after harvest. Crows also consume acorns, various wild and cultivated fruits, watermelon, wheat, sorghum, peanuts, pecans, garbage, and miscellaneous other items.

 

Ron J. Johnson. Extension Wildlife Specialist. Department of Forestry, Fisheries and Wildlife. University of Nebraska

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