Damage to Structures
Large roosts cause serious problems in some areas, particularly when located in urban sites. Roosts may be objectionable because of the odor of droppings, concerns for human health, noise, and damage to trees.
Damage to Livestock and Pets
In rare situations, crows attack very young calves, pigs, goats, and lambs, particularly during or shortly after birth. Depredation is more often associated with magpies or ravens, and is most likely to happen by crows where livestock births occur in unprotected, open fields near large concentrations of crows.
Crows sometimes consume the eggs and young of waterfowl, pheasants, and other birds during nesting season. Depredation may be locally severe where breeding waterfowl are concentrated and where little habitat exists to conceal nests. For example, crows find nests more easily when nests are located in narrow fence rows or at the edge of prairie potholes that have little surrounding cover. Crows typically consume large eggs (2.3 x 1.7 inches or greater) at the nest and may take smaller eggs from the site.
Damage to Landscapes
Complaints associated with damage by crows to crops were more common in the 1940s than they are today, apparently as a result of the response of crows to changing land-use patterns. Larger fields may reduce the proportion of crops lost to crows. Woodlands generally are smaller, and trees and other resources in urban areas provide more habitat for crows. The amount and degree of damage is highly variable among places and years. Several variables contribute to the complexity of problems created by crows, including season, local weather, time of harvest, crops produced, and availability and distribution of other food.
Crows may damage crops, though many problems are more commonly associated with other species of wildlife. Crows damage seedling corn plants by pulling the sprouts and eating the kernels. Similar damage also may be caused by other birds (pheasants, starlings, blackbirds) and rodents (mice, voles, squirrels). Crows damage ripening corn during the milk and dough stages, though such damage also is commonly caused by blackbirds. Crows consume peanuts when they are windrowed in fields to dry, but other birds, especially grackles, cause the most damage to peanuts. Crows also damage grain sorghum, commercial sunflowers, pecans, fruits, and watermelons.
Health and Safety Concerns
Crows and their roosts may threaten the safety of aircraft when their flight paths are near airports. In some situations, large flocks of crows may become a factor in spreading disease. When feeding in and around buildings that house swine, crows have been implicated in the spread of transmissible gastroenteritis (TGE).
Large flocks of crows near wetlands may increase the potential for the spread of diseases. The scavenging habits of crows and the apparent longer incubation time of avian cholera in crows are factors that increase the potential for crows to spread this disease. Roosts of crows, blackbirds, and starlings that have been in place for several years may harbor the fungus (Histoplasma capsulatum) which causes histoplasmosis, a disease that can infect people who breathe the airborne spores when soil at a roost site is disturbed. American crows are very susceptible to West Nile Virus (WNV) and are thought partly responsible for its rapid spread across the US. Fish crows also can contract WNV, but have a higher rate of survival.