Damage Prevention and Control Methods for Blackbirds

Type of Crop Damage

The red-winged blackbird (Agelaius phoeniceus).

Damage Prevention and Control Methods

Exclusion

Exclusion of blackbirds from agricultural crops is practical only for small gardens, experimental plots, and high-value fruit crops. Use lightweight netting to cover trees, bushes, or small plots. Protect individual ears of sweet corn in garden plots by placing paper bags over them after the silk has turned brown.

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Cultural Methods and Habitat Modification

Most economically severe blackbird damage to agricultural crops occurs in fields within 5 miles (8 km) of roosts. Thus, one strategy is to plant nonattractive crops—such as soy-beans, wheat, potatoes, or hay—in fields within a few miles of a roost. If crops vulnerable to damage, such as corn or sunflower, are planted near a roost, alternative feeding sites should be made available to reduce the feeding pressure on these cash crops. Delaying the plowing or tilling of previously harvested cropland near roosts to provide alternative feeding sites is one strategy to reduce damage to maturing crops. Also, fields near roosts should not be planted unusually early or late so that they mature in isolation from other fields in the area. In general, as alternative feeding sites decline, maturing grain or sunflower fields become more attractive to blackbirds, and keeping them out becomes more difficult.

Experimental programs are under way in sunflower production areas of the northern plains to thin out dense stands of cattails in marshes where large numbers of blackbirds roost. A registered herbicide (Rodeo^®) is applied in swaths to about 70% of the marsh. Thinning the cattail stands decreases blackbird roosts in the marsh and increases use by waterfowl for nesting and other activities.

Damage to sprouting rice fields planted near blackbird roosts in Louisiana and Texas can be substantially reduced by delaying planting until April. By this time, the large flocks of migrant blackbirds will have left for their northern nesting areas.

The timing of harvest can be very important in reducing damage to fields from flocks of blackbirds. For example, redwings inflict most damage to sweet corn at the time of fresh-market harvest, when the corn enters the milk stage. Timely harvest of sweet corn can substantially reduce damage. Although field corn generally becomes unattractive to birds when the kernels mature, sunflower, sorghum, and rice continue to be attractive after they mature and thus should be harvested as soon as possible.

Hybrids of corn with long husk extension and thick husks are more resistant to damage than other hybrids. Sorghum that contains a high tannin content is also less preferred than low-tannin varieties. For sunflower, birds prefer oil seed cultivars over the confectionery cultivars. Using sunflower cultivars with heads that turn downward as they mature and seeds with thick hulls should also help reduce feeding by blackbirds.

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Frightening

The use of frightening devices can be quite effective in protecting crops from flocks of blackbirds. Their use also requires hard work and long hours for the farmer, who needs to be persistent and innovative to keep one step ahead of the birds. Devices need to be employed especially in the early morning and in late afternoon when the birds are most actively feeding. Crops such as sweet corn, which are vulnerable to blackbirds for only a few days before harvest, may not be too difficult to protect; however, the task becomes more formidable for crops such as sunflower and sorghum, which may be vulnerable for up to six weeks. Propane exploders (some with timers that automatically turn them on and off each day) are the most popular frightening devices. In general, use at least one exploder for every 10 acres (4 ha) of crop to be protected. Elevate exploders on a barrel, stand, or truck bed to “shoot” over the crop, and move them around the field every few days. In addition, reinforce this technique occasionally with other scare devices. By shooting a .22 caliber rifle just over the top of a crop, a person on a stand or truck bed can frighten birds from fields of 40 acres (16 ha) or more. Obviously, care must be taken when shooting in this manner, and the use of limited range cartridges is recommended. Also effective are shell crackers, 12-gauge shotgun shells containing fire cracker projectiles that explode after traveling up to 150 yards (135 m). Shooting birds with a shotgun, using standard bird shot, often can kill a few birds and reinforce other scare devices. This technique, however, usually is not as effective in moving birds as the other devices that have greater range. Thus, a shotgun patrol should not be used as the sole means of frightening birds.

A variety of other bird-frightening devices, including electronic noise systems, helium-filled balloons tethered in fields, radio-controlled model planes, reflecting tapes made of mylar (Fig. 5), tape-recorded distress calls for birds, and various types of scarecrows, are also occasionally used to rid fields of blackbirds. The effectiveness of these devices is highly variable, depending on the persistence of the operator, the skill used in employing a device, the attractiveness of the crop, the number of birds, and the availability of alternate feeding sites. As mentioned with regard to propane exploders, birds tend to adjust or adapt to frightening devices. It is usually best to use two or more devices than to rely on a single device.

Figure 5. Mylar reflecting tape strung above the vegetation can reduce blackbird feeding activity in agricultural fields.

Avitrol^® is a registered chemical frightening agent for blackbirds in corn and sunflower fields. One out of every 100 particles of cracked-corn bait is treated with the chemical, 4-amino-pyridine. The bait is applied to fields in swaths, often by airplane, at the rate of 3 pounds per acre (3.3 kg/ha) to one-third of the field. The ingestion of one or more treated particles by a blackbird induces erratic flight, distress calls, and usually death. This behavior often causes the remaining birds in the flock to leave the field.

Careful consideration must be given to the timing of initial and repeat baitings. Begin baitings when birds first initiate damage, and repeat as necessary, typically at 5- to 7-day intervals. Dense weed populations that hide bait, ground insects such as crickets that eat bait, and excessive rainfall can contribute to making the product ineffective.

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Repellents

Methyl anthranilate (Fruit Shield^®) is currently registered for ornamentals, corn, sunflower, a variety of fruit crops and structures. Several seed-treatment repellents such as Ropel^® (active ingredient is benzyl diethyl ammonium saccharide) and Sevana Bird Repellent (ground garlic and pepper) have been registered to reduce bird damage to freshly planted and sprouting corn and other crops. However, the registration status of these products changes continually; thus, check with county extension agents or USDA-APHIS-Wildlife Services biologists for products currently registered.

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Toxicants

Starlicide is a registered toxicant for blackbirds and starlings in feedlot situations. The active ingredient, 3-chloro-p-toluidine hydrochloride, is incorporated into pelletized bait at a concentration of 0.1% and sold commercially under the trade name Starlicide Complete^®. Starlicide Technical^® (98% active ingredient), which can be custom-mixed with livestock feed or other bait material, is also available through the USDA-APHIS-Wildlife Services Program. Starlicide Technical^® can be used only by or under supervision of Wildlife Services employees.

Starlicide is a slow-acting toxicant; birds usually die 1 to 3 days after feeding. Baiting programs are most successful in winter, especially with snow cover present, when alternate foods are scarce. A successful program generally requires a period of prebaiting with nontoxic bait to accustom the target blackbirds and starlings to feed at specific bait sites inaccessible to livestock in the feedlot. Monitoring to ensure that nontarget birds such as doves, song birds, and barnyard fowl do not feed at bait sites is essential. See the chapter Starlings for more details on the use of Starlicide.

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Trapping

Certain species of blackbirds, particularly redwings, brown-headed cowbirds, and common grackles, often can be readily trapped in decoy traps. Consult a state wildlife official, such as a conservation officer or game warden, before putting a decoy trap into operation. A decoy trap is a large (for instance, 20x 20 x 6feet [6 x 6x 1.8 m]) poultry wire or net enclosure containing 10 to 20 decoy birds, food, and water (Fig. 6).

Figure 6. A typical blackbird and starling decoy trap showing elevated feed platform in center of trap and gathering cage on the far right. Birds enter the trap through a 2 x 4-foot (0.6 x 1.2-m) opening covered with 2 x 4-inch (5 x 10-cm) welded wire located directly above the feed platform.

Birds enter the trap through an opening (often 2 x 4 feet [0.6 x 1.2 m]) in the top of the cage that is covered with 2 x 4-inch (5 x 10-cm) welded wire. The blackbirds can fold their wings and readily drop through the openings to the food (generally cracked corn, millet, or sunflower seeds) below. A small (for example, 2 x 2 x 3 feet [0.6 x 0.6 x 0.9 m]) gathering cage with a sliding door attached to an opening at an upper corner of the trap can be used to collect trapped birds. A corralling baffle running about two-thirds the length of the trap can aid in driving the birds into the gathering cage.

A decoy trap often catches 10 to 50 blackbirds and starlings per day and occasionally up to 300 when located near a large roost. Obviously, the decoy trap is of questionable value in trying to reduce large roosting populations and damage to the surrounding agricultural fields. These traps, however, can be used to temporarily reduce local populations of blackbirds in special situations. For example, decoy traps have been used successfully in a six-county area of Michigan since the 1970s to reduce cowbird populations during the nesting season. This control was initiated to increase the nesting success of the Kirtland’s warbler (Dendroica kirtlandii), an endangered species whose nests are often used by cowbirds for laying their own eggs.

Each year about 3,500 cowbirds have been captured by decoy traps in this area of Michigan. Decoy traps might also be successful in reducing localized populations around feedlots or fruit crops.

Any nontarget songbirds accidentally captured in a decoy trap should be released immediately. Blackbirds to be disposed of should be killed humanely. They can be transferred from the gathering cage to a cardboard box or canvas-covered cage and asphyxiated with carbon dioxide gas. All dead birds should be examined for bands, and any bands found should be reported. One option for disposal that should not be overlooked is culinary. Blackbirds, being primarily grain eaters, make good food for humans! Recipes for quail or dove also work well for blackbirds.

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Shooting

As discussed under Frightening, shooting to kill with a shotgun is most effective when used occasionally to supplement or reinforce other scare devices. By itself, shooting with a shotgun is not cost-effective in frightening blackbirds from large agricultural fields, and it is totally ineffective as a means of reducing populations. Any killed birds should be examined for bands.

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