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; for further information, see 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 water-melons. 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.
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.
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 under-standing of bird problems in relation to agricultural and urban landscapes and other natural resource systems where damage occurs.