AMERICAN CROWS

The true crows are in the genus Corvus; they are large Passerine birds. As a group they show remarkable examples of intelligence; it would not be at all an exaggeration to characterize crows as being to birds what higher primates (including humans) are to mammals.

Identification
The American crow 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.

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.

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, then waited for passing automobiles to crack them. Crows are keen and wary birds. Consider the number of crows that scavenge along highways; 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 average 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 occasionally 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-cen-ter 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.

Damage and Damage Identification
Complaints associated with crow damage to agriculture were more common in the 1940s than they are today. Although surveys indicate that overall crow numbers have not changed appreciably, the populations appear to be more scattered during much of the year. This change has resulted apparently from the crows’ response to changing land-use patterns. Farming has become more prevalent in some areas, generally with larger fields. Woodland areas are generally smaller, and trees and other resources in urban sites provide crow habitat. Overall, the amount and degree of damage is highly variable from place to place and year to year. Several variables enter into the complex picture of crow damage, including season, local weather, time of harvest, amount of crop production, and availability and distribution of wild mast, insects, and other foods.

Although crows cause a variety of damage problems, many of these are more commonly associated with other animal species. Crows may damage seedling corn plants by pulling the sprouts and consuming the kernels. Similar damage may also be caused by other birds (pheasants, starlings, blackbirds) and rodents (mice, ground squirrels). Crows at times damage ripening corn during the milk and dough stages of development. Such damage, however, is more commonly caused by blackbirds. Crows consume peanuts when they are windrowed in fields to dry, but other birds, especially grackles, cause the greatest portion of this damage. Crows may also damage other crops, including ripening grain sorghum, commercial sunflowers, pecans, various fruits, and watermelons. In rare situations, crows may attack very young calves, pigs, goats, and lambs, particularly during or shortly after birth. This problem, which is more often associated with magpies or ravens, is most likely to happen where livestock births occur in unprotected open fields near large concentrations of crows.

Another complaint about crows is that they consume the eggs and sometimes the young of waterfowl, pheasants, and other birds during the nesting season. Overall, such crow depredation probably has little effect on the numbers of these birds. However, it can be a problem of concern locally, particularly where breeding waterfowl are concentrated and where there is too little habitat cover to conceal nests. For example, nests are more easily found by crows, as well as by other predators, when located in a narrow fence row or at the edge of a prairie pothole that has little surrounding cover.

Large fall and winter crow roosts cause serious problems in some areas, particularly when located in towns or other sites near people. Such roosts are objectionable because of the odor of the bird droppings, health concerns, noise, and damage to trees in the roost. In addition, crows flying out from roosts each day to feed may cause agricultural or other damage problems. On the other hand, the diet of crows may be beneficial to agriculture, depending on the time of year and surrounding land use (see sections on crow food habits and economics).

Finally, in some situations, large crow flocks may become a factor in spreading disease. At times, they feed in and around farm buildings, where they have been implicated in the spread of transmissible gastroenteritis (TGE) among swine facilities. At other times, large crow flocks near wetland areas may increase the potential for spread of waterfowl diseases such as avian cholera. The scavenging habits of crows and the apparent longer incubation time of the disease in crows are factors that increase the potential for crows to spread this devastating disease. Also, crow and other bird (blackbird, starling) roosts that have been in place for several years may harbor the fungus (Histoplasma capsulatum) that causes histoplasmosis, a disease that can infect people who breathe in spores when a roost is disturbed.

Economics of Damage and Control
The economics of crow damage often center around a widespread controversy over whether crow feeding habits are harmful or beneficial. Some say that crows earn their keep by taking harmful insects and cleaning up carrion. Others say the damage done far outweighs any beneficial aspects. Despite some studies of the crow diet, little quantitative information is available on the overall economic impacts of crows. In addition, it appears likely that the economics of crows in relation to agriculture or people have changed from what they were 30 or more years ago when many crow studies were done.

At one time several state legislatures appropriated funds for bounties on crows and for bombing crow roosts, and suggested all-out efforts to eradicate the crow. Now, most state wildlife and agriculture departments report only a few scattered complaints of crow damage each year. At times, however, individual farms or crops do suffer severe damage, and concerns about large crow roosts in urban areas near people appear to be increasing. Individuals experiencing damage problems should weigh the costs of control against the amount of damage, then work with the proper authorities to develop a control program.

On the beneficial side, the crow diet includes large numbers of insects considered harmful to agriculture, as well as mice and carrion. In addition, their consumption of waste grain left in fields may help prevent undesirable volunteer corn in the following year’s crop. The fact that crows also eat snakes may be considered a benefit by some people.

Overall, crow and other bird problems can be difficult or frustrating to resolve satisfactorily with the methods and understanding currently available. Persistence and use of a variety of techniques may be necessary to help prevent damage. In addition, further research is needed to develop damage control methods based on an understanding of bird problems in relation to agricultural and urban landscapes and other natural resource systems where damage occurs.

Legal Status
Crows are protected by the Migratory Bird Treaty Act, a federal act resulting from a formal treaty signed by the United States, Canada, and Mexico. However, under this act, crows may be controlled without a federal permit when found “committing or about to commit depredations upon ornamental or shade trees, agricultural crops, livestock, or wildlife, or when concentrated in such numbers and manner to constitute a health hazard or other nuisance.”

States may require permits to control crows and may regulate the method of take. Federal guidelines permit states to establish hunting seasons for crows. During these seasons, crows may be hunted according to the regulations established in each state. Regulations or interpretation of depredation rules may vary among states, and state or local laws may prohibit certain control techniques such as shooting or trapping. Check with local wildlife officials if there is any doubt regarding legality of control methods.


Damage Prevention and Control Methods

Exclusion
Netting to exclude crows from high-value crops or small areas. Protect ripening corn in gardens by covering each ear with a paper cup or sack after the silk has turned brown. Widely-spaced lines or wires placed around sites needing protection may have some efficacy in repelling crows, but further study is needed.

Cultural Methods
Alternate or decoy foods; example: scatter whole corn, preferably softened by water, through a field to protect newly planted corn seedlings.

Frightening
Use with roosts, crops, and some other situations. Frightening devices include recorded distress or alarm calls, pyrotechnics, various sound-producing devices, chemical frightening agents (Avitrol®), lights, bright objects, high-pressure water spray, and, where appropriate, shotguns.

Repellents
None are registered.

Toxicants
None are registered.

Trapping
Check laws before trapping. Australian crow decoy traps may be useful near a high-value crop or other areas where a resident population is causing damage. Proper care of traps and decoy birds is necessary. Capture single crows uninjured in size No. 0 or No. 1 steel traps that have the jaws wrapped with cloth or rubber.

Shooting and Hunting
Helpful as a dispersal or frightening technique but generally not effective in reducing overall crow numbers. Crows may be hunted during open seasons. Check with your state wildlife agency for local restrictions.




ACKNOWLEDGEMENTS
The above information was adapted from PREVENTION AND CONTROL OF WILDLIFE DAMAGE with permission of the editors, Scott E. Hygnstrom, Robert M. Timm, and Gary E. Larson (Cooperative Extension Division, Institute of Agriculture and Natural Resources University of Nebraska-Lincoln, United States Department of Agriculture Animal and Plant Health Inspection Service, Animal Damage Control, Great Plains Agricultural Council Wildlife Committee).