Economics of Damage and Control Go back to Blackbirds
Superficial surveys of agricultural fields often overestimate blackbird damage and thus exaggerate the overall severity of the economic threat for one of four reasons: (1) the conspicuousness of blackbird flocks tends to heighten the awareness of bird damage compared with other more subtle forms of loss caused by weeds, insects, other pests, and harvesting; (2) the eye naturally seeks out the conspicuously bird-damaged plants; (3) bird damage is often most severe along field edges where an observer is most likely to check; and (4) raccoon, other mammal, or wind damage is sometimes mistaken for bird damage (see the section Damage Identification and Assessment). This is not to downgrade the problem of blackbird damage in agriculture; damage can be economically severe on occasion and quite frustrating to the farmer when relief is not readily available. It is important, however, to obtain objective estimates of damage levels likely to occur, for only then can intelligent decisions be made regarding the amount of money and effort to be invested on control. The final decision on control measures must take into account the value of the crop, cost of control, and the degree of effectiveness of the control measure in relation to the probable levels of damage.
Studies during the past two decades concerning blackbird damage to various crops such as corn and sunflower indicate that on statewide or regional bases, overall mean damage is low, generally less than 1% of the crop. If all farmers received less than 1% damage, there would be little concern; however, the damage is not equally distributed. While most farmers escape economically serious damage, a few farmers receive serious damage. For example, in North Dakota, South Dakota, and Minnesota in 1979 and 1980, overall loss of sunflower to blackbirds was estimated to be only 1.2% of the crop. Yet, 2% of the fields received more than 10% loss. Only in these relatively few fields that sustain high levels of damage can control measures generally be cost-effective.
While accurate prediction of damage is often impossible to obtain, knowledge of the location of a field in relation to traditional roosting sites often provides the basis for a sound estimate of potential damage. For example, studies of blackbird damage to ripening corn in Ohio have revealed that almost all losses exceeding 5% of the crop have occurred in fields within 5 miles (8 km) of marsh roosts.
Objective estimates of damage levels in previous years for the same or nearby fields are another means of predicting future damage levels, because bird damage is fairly consistent from year to year within a locality. This information also provides a good baseline for evaluating the effectiveness of management strategies. Of course, it is important that estimates be objective and apply to the entire field.
Legal Status
Blackbirds are native migratory birds, and thus come under the jurisdiction of the Federal Migratory Bird Treaty Act, a formal treaty with Canada and Mexico. Blackbirds are given federal protection in the United States. They may be killed only 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 as to constitute a health hazard or other nuisance,” as stated in federal laws regarding migratory birds (50 CFR 21). Some states have additional restrictions on the killing of blackbirds.
Damage Prevention and Control Methods
Exclusion
Generally not practical; netting can be used on small plots. Netting is cost-effective for high-value crops.
Cultural Methods
Deep planting, avoid early planting of rice. Grow nonpreferred crops near roost; provide alternative feeding sites. Avoid early or late planting; use resistant hybrids. Harvest as early as possible. Same as for ripening corn except resistant hybrids are not available. Provide alternative feeding site; early harvest.
Frightening
Several devices available; most popular is propane exploder.
Repellents
Seed treatments.
Toxicants
None available.
Trapping
Generally not practical.
Shooting
Helpful to reinforce frightening devices, futile for population reduction.
Learn More About:
RED-WINGED BLACKBIRD
COMMON GRACKLE
BROWN-HEADED COWBIRD
YELLOW-HEADED BLACKBIRD
BREWER'S BLACKBIRD
RUSTY BLACKBIRD
Please read more about us and our bird removal services . You can also learn about Cowleys history and understand why to choose Cowleys for bird exclusion. You can read about what physical or visual bird deterrents are used and what to do if nuisance birds are taking over your business.
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