BLACKBIRDS

The term blackbird loosely refers to a diverse group of about 10 species of North American birds that belong to the subfamily Icterinae. In addition to blackbirds, this subfamily includes orioles, meadowlarks, and bobolinks. The various species of blackbirds have several traits in common. The males are predominantly black or iridescent in color. All blackbirds have an omnivorous diet consisting primarily of grains, weed seeds, fruits, and insects. The relative proportions of these food groups, however, vary considerably among species. Outside of the nesting season, blackbirds generally feed in flocks and roost at night in congregations varying from a few birds to over one million birds. These flocks and roosting congregations are sometimes comprised of a single species, but often several species mix together. Sometimes they are joined by non-blackbird species, notably European starlings (Sturnus vulgaris) and American robins (Turdus migratorius).

The species also have many important differences in their nesting biology, preferred foods, migration patterns, and their damage and benefits to agriculture. Summarized below for each of seven species of blackbirds is information on identification, geographic range, preferred habitats, feeding habits, general biology, and damage.


RED-WINGED BLACKBIRD (Agelaius phoeniceus)

Identification
The male, a little smaller than a robin, is black with red and yellow shoulder patches. The smaller female is brownish, resembling a large sparrow.

Range and Habitat
An abundant nester throughout much of North America, the red-winged blackbird nests in hayfields, marshes, and ditches. Large flocks feed in fields and bottomlands. Redwings winter in the southern United States.

Food Habits and General Biology
Insects are the dominant food during the nesting season (May through July), with the diet shifting predominantly to grain and weed seeds in late summer through winter. Males and females often forage in separated flocks, with females being more insectivorous than males. Except during nesting season, redwings congregate in large nighttime roosts in marshes or woods containing up to several million birds. Annual survival rate is only about 50% to 60%. This high mortality rate is offset by a reproductive rate of 2 to 4 young fledged per female per year. Females have 3 to 5 eggs in their open-cup nests made of grasses and other vegetation. Eggs hatch after 12 days of incubation; the young grow rapidly and are ready to fledge about 10 days later. Females will often renest if their initial nest is destroyed.

Damage to Crops
Red-winged blackbirds can cause considerable damage to ripening corn, sunflower, sorghum, and oats in the milk and dough stages, and to sprouting and ripening rice. These birds provide some benefits by feeding on harmful insects, such as rootworm beetles and corn earworms, and on weed seeds, such as Johnson grass.


COMMON GRACKLE (Quiscalus quiscula)

Identification
An iridescent blackbird larger than a robin, the common grackle has a long keel-shaped tail. The male, slightly larger than the female, has more iridescence on the head and throat.

Range and Habitat
A common nester throughout North America east of the Rockies, the common grackle nests in shelterbelts, farmyards, marshes, and towns. Flocks feed in fields, lawns, woodlots, and bottomlands. These birds winter in the southern United States, often in association with redwings, cowbirds, and starlings.

Food Habits and General Biology
The common grackle’s diet is somewhat similar to that of the redwing, but the grackle is more predatory. Its diet occasionally includes small fish, field mice, songbird nestlings, and eggs. Grackles have a larger, stronger bill than redwings, allowing them to feed on acorns and other tree fruits in winter. The common grackle (Quiscalus quiscula) is an iridescent blackbird, larger than a robin, with a long, keel-shaped tail. Grackles often roost with redwings, but are more partial to roosting sites in upland deciduous or pine trees. Reproductive and survival rates are similar to redwings.

Damage to Crops
Damage is similar to that of redwings; however, grackles will feed on mature field corn in the dent stage, removing entire kernels from the cob. Also, grackles will pull up sprouting corn.


GREAT-TAILED GRACKLE (Quiscalus mexicanus)

Identification
This species is similar to the common grackle but with a much larger tail. The male is slightly smaller than a crow; the female is smaller and browner than the male.

Range and Habitat
An abundant year-round resident in coastal and southern Texas, the great-tailed grackle nests in colonies in shrubs or trees, sometimes in association with herons and egrets. The flocks feed around farms, pastures, and parks.

Food Habits and General Biology
The diet is omnivorous: insects, aquatic organisms, eggs from nesting birds, fruits, and grains. Reproductive and survival rates are similar to those of redwings.

Damage to Crops
These birds damage all types of fruits and melons, although the loss is generally minor. In recent years, however, their damage to citrus crops in localized areas of the lower Rio Grande Valley of Texas has been substantial. Great-tails peck the citrus fruit skin, creating blemishes or holes.


BROWN-HEADED COWBIRD (Molothrus ater)

Identification
The male is black with a brown head and the female is gray. Both sexes have sparrowlike bills. The brown-headed cowbird (Molothrus ater), smallest of the blackbirds, often feeds in close association with livestock. The female cowbird lays her eggs in the nests of other birds.

Range and Habitat
Cowbirds occur in spring and summer throughout much of North America. Flocks feed in pastures and feedlots, and are often associated with livestock. Cowbirds winter in the central to southern United States, often roosting with redwings, grackles, and starlings.

Food Habits and General Biology
The diet of cowbirds consists predominantly of weed seeds and grains, and less than 25% insects. Cowbirds do not build nests or incubate eggs; the female lays her eggs in nests of other songbirds, the only North American songbird to do so. Females deposit 1 or sometimes 2 eggs per host nest, laying up to 25 or more eggs per nesting season.

Damage to Crops
This species can cause damage to ripening sorghum, sunflower, and millet. Cowbirds consume some livestock feed, but often glean waste grain and seed from dung. Overall damage is usually minor.


YELLOW-HEADED BLACKBIRD (Xanthocephalus xanthocephalus)

Identification
A robin-sized bird, the male has a striking appearance with his black body, conspicuous yellow head and breast, and a white wing patch in flight. The female is smaller and browner, with a yellowish throat and breast.

Range and Habitat
Yellowheads are locally abundant nesters in deep-water marshes of the northern Great Plains and western North America. They feed in agricultural fields, meadows, and pastures during late summer and fall, sometimes in association with redwings or other blackbirds. They winter farther south than other blackbirds, primarily in Mexico.

Food Habits and General Biology
The diet is similar to that of redwings; yellowheads eat primarily insects during the nesting season and grains and weed seeds at other times. An early
migrant, the yellowhead leaves the northern plains by September. Survival and reproductive rates are similar to those of redwings.

Damage to Crops
Yellowheads cause localized but generally minor damage to ripening corn, sunflower and oats, often in association with redwings. They often leave the northern prairie regions by the time corn and sunflower are ripening in autumn.


BREWER'S BLACKBIRD (Euphagus cyanocephalus)

Identification
A robin-sized bird, the male is all black confused with whitish eyes; the female is brownish gray with dark eyes.

Range and Habitat
A familiar bird in the northern Great Plains and western North America, the Brewer’s blackbird nests in a diversity of habitats. It prefers pastures, lawns, and agricultural lands for feeding. It is a winter migrant in the central and southern Plains states, sometimes roosting with other black bird species.

Food Habits and General Biology
The diet is about two-thirds grain and weed seeds, and one-third insects and other animal matter. They feed in flocks on waste grain and weed seeds and nest in colonies. Reproductive and survival rates are similar to those of redwings.

Damage to Crops
Brewer’s blackbirds cause generally minor damage to oats, fruit crops, and livestock feed and consume large numbers of noxious insects during the summer months.


RUSTY BLACKBIRD (Euphagus carolinus)

Identification
Similar to Brewer’s blackbird, its fall and winter plumage has a rusty coloration.

Range and Habitat
Rusty blackbirds nest in northern swamps and muskegs (bogs) throughout Canada, Alaska and northern New England. They migrate in winter to the southern United States from the Atlantic coast to east Texas.

Food Habits and General Biology
The diet of rust blackbirds is more insectivorous than that of other blackbirds. Over 50% of their food is animal matter. Grain (gleaned from harvested fields in fall and winter),weed seeds and tree fruits are also eaten. In winter, rusty blackbirds prefer swampy areas and river bottoms. They often roost with other blackbirds.

Damage to Crops
This species does little crop damage.


Economics of Damage and Control
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.




ACKNOWLEDGEMENTS
The above information was adapted from PREVENTION AND CONTROL OF WILDLIFE DAMAGE with permission of the editors, Scott E. Hygnstrom, Robert M. Timm, and Gary E. Larson (Cooperative Extension Division, Institute of Agriculture and Natural Resources University of Nebraska-Lincoln, United States Department of Agriculture Animal and Plant Health Inspection Service, Animal Damage Control, Great Plains Agricultural Council Wildlife Committee).