BLACKBIRDS and their Biology

 

Richard A. Dolbeer
Project Leader
Denver Wildlife Research Center
USDA-APHIS-Wildlife Services
Sandusky, Ohio 44870

For additional information on blackbird control click Blackbird Control

Fig. 1. The red-winged blackbird Fig. 1. The red-winged blackbird (Agelaius phoeniceus) is the most abundant bird in North America. The black male, with red and yellow shoulder patches, is about 40% larger than the female. The female resembles a large sparrow more than a blackbird.

redwinged blackbirds

Introduction

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 (Fig. 1).

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)

Common Grackle (Quiscalus quiscula)

Fig. 2. The common grackle (Quiscalus quiscula) is an iridescent blackbird, larger than a robin, with a long, keel-shaped tail.

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 (Fig. 2).

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. 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 Cowbirds (Molothrus ater)

The cowbird is the smallest blackbird. The male is black with a brown head and the female is gray. Both sexes have sparrowlike bills (Fig. 3).

Fig. 3. The brown-headed cowbird (Molothrus ater), smallest of the blackbirds, often feeds in close association with livestock. The female cowbird (lower) 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 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 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 blackbird 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 rusty 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 blackbird species.

Damage to Crops

This species does little damage to crops.

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.

Editors

Scott E. Hygnstrom; Robert M. Timm; Gary E. Larson

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