Blackbirds and starlings are abundant and congregate in large flocks, and they may be involved in a wide range of conflicts. Damage problems associated with these birds occur in agricultural settings as well as in urban/suburban areas.
Damage to Property
Because blackbirds and starlings congregate in large groups, their feces can be excessive and cause health concerns and property damage. Large roosts that occur in buildings, industrial structures, or in trees near homes are a problem because of health concerns, filth, noise, and odor. In addition, slippery accumulations of droppings pose safety hazards at industrial structures, and the acidity of droppings is corrosive.
Damage to Agriculture
Blackbirds and starlings damage agricultural crops causing significant economic losses to agricultural producers. The estimated annual damage to grain, fruit, and berry crops from blackbirds and starlings exceeds $150 million in direct costs. Additional costs, not estimated, include those spent to prevent health and safety hazards and those from damage management efforts. Blackbirds and starlings also congregate at cattle feedlots, where they consume and contaminate livestock feed, and could potentially transmit disease. Blackbirds and starlings are known to eat the high protein supplements given to cattle. These bird species can also transmit disease from one livestock facility to another through their droppings.
Health and Safety Concerns
European starlings and blackbirds pose aircraft safety hazards because of the potential for these birds to collide with aircraft, resulting in aircraft damage or loss, and human death and injury. Flocks of blackbirds and starlings are especially hazardous due to the great numbers of birds in the flocks, their flight behaviors, and their overall abundance across the United States. In 1960, 62 people aboard a commercial aircraft were killed after the plane collided with a flock of starlings at Boston's Logan Airport. During 1990-2008, a total of 3,496 blackbird and starling bird strikes were recorded for U.S. civil aviation, resulting in more than $5 million in damage.
When large flocks of blackbirds and starlings roost, accumulations of droppings are common. One health concern associated with blackbird roosts is the fungal respiratory disease, Histoplasmosis. The fungus that causes the disease ( Histoplasma capsulatum) occurs in the soil in bird roosts where excessive droppings have accumulated. Although this disease is rare, it can be a concern for people with weakened immune systems.
Damage to Natural Resources
Brown-headed cowbirds' behavior of laying their eggs in the nests of other birds is beneficial to the cowbird, but detrimental to the host bird species. The cowbird chicks, which hatch earlier than most songbirds, aggressively out-compete the host species' chicks for food. Often, the songbird chicks die and the cowbirds thrive. Cowbird parasitism is believed to have been a major factor in the decline of the Kirtland's warbler, a Federally endangered songbird that nests only in young stands of jack pine in Michigan, Wisconsin and Canada.
Starlings can impact native birds by competing for food and other habitat resources. Where nest cavities are scarce, starlings and blackbirds are adept at occupying them and excluding native cavity nesting species such as bluebirds, flickers, woodpeckers, and purple martins.