New World Blackbirds and Orioles (Icteridae)

(vertebrate zoology) The troupials, a family of New World perching birds in the suborder Oscines.

(Icteridae)

Class: Aves

Order: Passeriformes

Suborder: Passeri (Oscines)

Family: Icteridae

Thumbnail description
Medium to large-sized songbirds with short and massive to rather long and slender conical bills; many are colorful and sexually dimorphic in both size and coloration

Size
6.7–21.5 in (17–55 cm); 0.6 oz–1.2 lb (16–528g)

Number of genera, species
25 genera; 103 species

Habitat
Forest, woodlands, marshes, and grassland

Conservation status
Critically Endangered: 3 species; Endangered: 4 species; Vulnerable: 4 species; Near Threatened: 1 species; Extinct: 1 species

Distribution
North, Central, and South America (Alaska to Cape Horn)

Evolution and systematics

The New World blackbirds, troupials, and meadowlarks (Icteridae) include the beautiful orioles (Icterus) and caciques (Cacicus), as well as many other colorful songbirds. The icterids are variously treated as a family, subfamily, or tribe in a more inclusive family (Emberizidae or Fringillidae) that also contains a number of other songbirds having only nine primary wing feathers. Most sources separate these at the familial level. Other groups of birds that are closely related to the blackbirds are the olive warbler (Peucedramus taeniatus), bananaquit (Coereba flaveola), and other New World warblers (Parulidae), and the tanagers, buntings, and other New World finches (Emberizidae). These birds no doubt evolved in the New World, and today all, with the exception of the Emberizidae, are confined in their distribution to the New World. The Icteridae almost certainly evolved in South America where today the largest number of species occur. One large genus of blackbirds, the orioles, may be of Central American origin. These families probably differentiated rather recently in geological time, perhaps during the Pliocene. All of the fossils of icterids, however, are from the Pleistocene or Holocene.

Molecular studies delineate five distinct lineages within the Icteridae. These are: (1) the grackles and allies (including Agelaius, Euphagus, Quiscalus, Molothrus, and 11 other genera), (2) the caciques and oropendolas (Cacicus and Psarocolius), (3) the orioles (Icterus), (4) the meadowlarks and allies (Dolichonyx, Xanthocephalus, Sturnella, and Leistes), and (5) the cup-nesting caciques (Amblycercus holosericeus).

Physical characteristics

Icterids are remarkably diverse in size. They range from the slim orchard oriole (Icterus spurius), which weighs as little as 0.6 oz (16 g), to the robust Montezuma's oropendola (Psarocolius montezuma), which can weigh as much as 1.2 lb (528 g), making it one of the largest songbirds. Most species are brightly colored, commonly with black (often with a bright metallic gloss) and yellow, but many species have prominent red coloration, and some of the oropendolas are greenish. Some species have a neck ruff; others, a sparse crest.

The family name comes from the Greek ikteros which was a yellow bird, perhaps the golden oriole (Oriolus) which was thought to cure jaundice. The English vernacular name for the New World orioles (Icterus) was given to them by early naturalists who thought them to be related to the Oriolus orioles of the Old World, but today it is realized that these birds are not closely related.

There is a great deal of variation in bill size and shape in the Icteridae. Many blackbirds have rather long, stout, and pointed bills; the ridge of the upper mandible is often straight in profile, and may extend onto the forehead, forming a frontal shield. Some of the orioles have slim, gracile bills that are slightly downturned, and the bobolink (Dolichonyx oryzivorus) and some of the cowbirds (Molothrus) have a finch-like conical bill. Blackbirds—particularly those species that forage extensively on the ground—have rather large legs and long claws.

Many species of blackbirds are strikingly sexually dimorphic in size. This is especially true in species where males are commonly polygynous (a male will be mated to two or more females in a single breeding season), e.g., Psarocolius, Agelaius, Quiscalus, and Xanthocephalus. As well, many blackbirds are sexually dimorphic in color. In dimorphic species, the males tend to have a bright display plumage whereas females are dull and relatively inconspicuous; the young tend to resemble females, and males may not develop their full display plumage until they are two years of age. Plumage dimorphism is characteristic of icterids that breed in north temperate areas. Within the orioles, the species that breed in North America, including some of the Mexican species, are dimorphic in color, whereas the tropical species (including the three South American species) are monomorphic (although the female is sometimes somewhat less brightly colored).

Distribution

New World blackbirds are widespread in the New World, and, with the exception of a few records of vagrant individuals, they are confined to the New World. The species with the northern-most range, the rusty blackbird (Euphagus carolinus), breeds from the limit of trees in northern Alaska, northern Yukon, southwestern Nunavut, and Labrador southward into central Alberta and into northern-most parts of the northeastern United States. The species with the southernmost range, the austral blackbird (Curaeus curaeus), is found south to Cape Horn, and the long-tailed meadowlark (Sturnella loyca) breeds from Chile and Argentina south to the Beagle Channel Islands in Tierra del Fuego and in the Falkland Islands. Between these extremes, there is no place in the Americas where there is not at least one breeding icterid. The areas of the greatest richness of species are southern Mexico, northwestern South America, and southern Brazil, Paraguay, Uruguay, and northeastern Argentina. The genus with the largest number of species, Icterus, reaches its greatest richness in Central America where nine species breed, and an additional three species winter. The oropendolas (Psarocolius), which are forest dwelling, are confined to the Neotropics; two species are found north to the humid forests of southern Mexico. Nine of the 10 species of caciques likewise are limited to the Neotropics, although one species does range north to the Pacific coastal lowlands of central Sinaloa. The genus Euphagus, with two species, is the only genus restricted in range to North America (one winters south to central Mexico). The grackles (Quiscalus), which are closely related to the Euphagus blackbirds, are also found in North America, but some species are also found in Central and northern South America and in the Caribbean. Several studies have indicated that the blackbirds that are presently placed in the genus Agelaius should be divided into two genera, one found in North and Central America and the Caribbean, and the other confined to South America.

Habitat

New World blackbirds are found in a variety of different habitats, such as forests, savanna, grasslands, deserts, marshes, and bogs. The caciques and oropendolas are all found in forests, commonly humid lowland tropical forests. Many species, however, are associated with forest edge or clearings and are not generally found in the forest interior, and some are found in montane cloud forests. The yellow-winged cacique (Cacicus melanicterus), which occurs north to at least central Sinaloa, Mexico, may be found in thorn scrub, plantations (coconuts, mangos) and other settled areas, and in mangroves.

Most of the orioles (Icterus), the melodious, Brewer's, and yellow-shouldered blackbirds (Dives dives, Euphagus cyanocephalus, and Agelaius xanthomus), and the common and greater Antillean grackles (Quiscalus quiscula and Q. niger) are found in open woods, early successional habitats, riparian woods, savannas, or urban areas. The bobolink, meadowlarks (Sturnella), and the brown-headed cowbird (Molothrus ater) are found in grasslands, the yellow oriole (I. nigrogularis) and Bolivian blackbird (Oreopsar bolivianus) are found deserts, and the rusty blackbird occurs in boreal bogs. Lastly, a large number of blackbirds nest in marshes. Included in this group are the widespread and familiar North American red-winged blackbird (Agelaius phoeniceus) and other species in this genus, the yellow-headed blackbird (Xanthocephalus xanthocephalus), the marshbirds (Pseudoleistes), and the scarlet-headed blackbird (Amblyramphus holosericeus) of South America, and several of the grackles. Many of these marsh-nesting blackbirds are colonial or breed in grouped territories.

Behavior

Although they may occasionally sing during the night, blackbirds are diurnal. During migration and winter, many species form flocks—sometimes huge flocks—when they are both foraging and roosting. In the mid-1970s, there were 723 major roosting flocks in the United States containing an estimated 438 million blackbirds. An estimated 200 million icterids winter in Arkansas, Louisiana, Tennessee, and Mississippi. In the west, particularly in rice growing areas of east Texas and California, another 139 million icterids winter, and in North Carolina about 76 million winter. There are advantages to the birds in these large roosting flocks. There is strength in numbers: there are more birds to sight potential predators, and it can be dangerous for flying predators to enter a large flock of birds. There is also protection from rain, wind, and heat loss in a large flock. A disadvantage is that there is not sufficient food close to a large roost to feed the large numbers of birds present, and some individuals must travel up to 60 mi (100 km) each direction every day to reach feeding areas where the food has not already been depleted. Migrating and wintering blackbirds often forage in flocks as well, but foraging flocks are generally smaller than roosting ones. New World blackbirds walk rather than hop on the ground.

Blackbirds perform a wide variety of displays, many of which are quite interesting to watch. One common and widespread icterid display is the "song-spread" (or "rough-out") display. In this display, the bird (most commonly a male, but females of some species also do this) spreads its wings somewhat, and raises the feathers on its shoulders, back, and neck; on the red-winged blackbird this displays the bright red epaulets prominently. Some birds, such as some of the cowbirds (Molothrus), have a neck ruff that is exaggerated during this display. The "song-spread" display is accompanied by song. The "song-spread" appears to function both in territorial defense and for mate attraction. The "bill-tilt" display is another display that many blackbirds use. In this display, the feathers are sleeked, and the bill, head, and body are pointed upward. "Bill-tilting" is aggressive, and is used during encounters both within and between sexes. Many blackbirds have "flight-song" displays, and in some species these displays can be spectacular. Male white-browed blackbirds (Sturnella superciliaris) fly to a height of about 60 ft (20 m) and parachute to the ground while giving their song. The "flight-song" of the bobolink is also spectacular. The male, with a fluttery flight and wings bowed—not rising above the horizontal, and tail pointed downward, fly up to perhaps 30 ft (10 m) from the ground while uttering their bubbling song. Male redwinged blackbirds commonly give a rapid series of notes, "tseee tch-tch-tch-tch chee-chee-chee" while in flight. Female blackbirds characteristically arch their backs, and with their heads down raise their tails and shiver their wings in a pre-copulatory display. Injury feigning distractions are given by some blackbirds, but are not common in the family. Male oropendolas perform a "bow-display." In this display, the male sits on a branch, partially opens his wings, thrusts his head downward and tail upward, until he is completely upside down, with his tail at right a right angle to his body, then rights himself as he finishes his song, and shakes his wings.

Feeding ecology and diet

The largely arboreal oropendolas, caciques, and orioles commonly forage by gleaning food from vegetation in trees. These birds, like many other blackbirds, often feed by gaping—inserting their closed bills into a flower, fruit, or stem, then opening the bill to expose food or facilitate nectar feeding. Twigs and branches often harbor small insects, especially ants. By gaping into these branches, birds capture these insects. Bark can be pried loose by gaping, and yellow-backed orioles (Icterus chrysater) gape under the scales of pine cones, as well as flake away bark, in the search for insects. Black caciques, such as the Ecuadorian cacique (Cacicus sclateri), split the slender stems of bamboo to find insects, but like most blackbirds are generalists when foraging, eating fruit and nectar in addition to insects. An oriole often gapes when eating fruit: it thrusts its closed beak into the fruit, then opens it and uses its tongue to drink the laked juice. They also forage for nectar (or sugar in hummingbird or oriole feeders) and many commonly forage on the ground.

The species of blackbirds that live in grasslands feed mostly on the ground, and the marsh-dwelling species also commonly feed on the ground, especially in the winter. Meadowlarks commonly feed by gaping. They insert their long bills into the ground, then open the mandibles to expose insect prey or grain; the muscles used for opening the bill are particularly well-developed in these birds. Particularly during the winter, many blackbirds forage extensively on the ground for grain and other seeds, and some species eat small vertebrate animals. Red-winged blackbirds have been observed to eat Nelson's sharp-tailed sparrows (Ammodramus nelsoni), and rusty blackbirds and grackles have been observed eating birds as large as white-throated sparrows (Zonotrichia albicollis). Grackles are also adept at catching small fish in shallow waters, and they can crush acorns with their powerful bills. Black-backed orioles (I. abeillei) are one of the few birds that will eat the often toxic monarch butterflies (Danaus plexippus). The toxicity of these butterflies is derived from some of the plants that they eat, and the majority of the butterflies are only weakly toxic. The orioles taste each butterfly that they capture, and release the more toxic ones. Blackbirds are not adept at flycatching, but they do take some low-flying insects. In winter, many species of blackbirds forage in flocks on the ground. Commonly these flocks are composed of mixed species. In North America, flocks often contain a combination of cowbirds, grackles, red-winged blackbirds and, in the west, yellow-headed blackbirds and Brewer's blackbirds. When the birds are foraging, these flocks appear to roll along as the birds toward the back of the flock fly to the front of the flock as it moves along.

Reproductive biology

Most icterids build an open cup-shaped nest, woven into supporting vegetation or in a crotch in a shrub. Hole nesting is extremely rare in blackbirds, but occasionally nests are placed cavities. The only species that regularly nests in holes is the Bolivian blackbird, which nests in arid areas on the eastern slope of the Andes, where there are few trees or shrubs. Thus, it is not surprising that they place their nests in crevices in cliffs. Baywings (formerly called the bay-winged cowbird) (Agelaioides badius) usually lay their eggs in nests built by other species of birds, and they seem to prefer the domed nests of ovenbirds (Furnariidae); they also will nest in nest boxes. Orioles, caciques, and oropendolas weave distinctive pendant bag nests, which are suspended from the branches of trees, although in Louisiana, where they often nest in marshes; orchard orioles (Icterus spurius) often weave their nests into supporting reeds. Nests of oropendolas may be over 50 in (125 cm) long. The nests of grassland icterids usually are placed on the ground, often a nest woven of fine grass, and placed at the base of a tuft of grass that may overhang the nest. The nests of some of the meadowlarks are domed, and there may be runways in the grass leading to the nest. The cowbirds (Molothrus) are brood parasites, that is, they lay their eggs in the nests of other species of bird. Some of these, such as the brown-headed and shiny cowbirds (M. ater and M. bonariensis) parasitize a large number of host species, but the screaming cowbirds (M. rufoaxillaris) lay their eggs only in the nests of baywings, and a few other species of blackbirds. Many species of blackbirds are colonial, or at least have grouped territories. Nest building is done exclusively or principally by the female. The number of eggs and their shape and coloration varies among species. Some oropendolas may lay only a single egg, whereas the parasitic brown-headed cowbird may lay a great many eggs in any season (perhaps 30; one captive female laid 77), but these tend to be laid daily, in sequences of one to seven eggs. They vary in shape from rather round to elongated; they are glossy and tend to be marked with spots and blotches, although some cowbirds may lay unmarked eggs.

Most blackbirds are at least socially monogamous, but a great many species are polygynous. Polygyny seems to be particularly frequent in colonial marsh-nesting blackbirds and many of the colonial caciques and oropendolas. In the polygynous crested oropendola (Psarocolius decumanus), females greatly outnumber males, perhaps by as much as 10 to one in some populations. The much-studied red-winged blackbird commonly is polygynous, but some individuals are monogamous; in this species—and probably many others—extra-pair copulations are common. Females appear to solicit such copulations. A male red-winged blackbird may have as many as 15 mates. Not surprisingly, males give more assistance to females in monogamous pairs than in polygynous ones. The marsh-nesting scarlet-headed blackbird of South America, and some other marsh-nesting species, however, are monogamous.

Conservation status

Many species in the Icteridae are among the most numerous and successful of American songbirds. They are a conspicuous component of the fauna of many grasslands and marshes, and some, such as many of the grackles and cowbirds, have adjusted well to human-induced changes to the environment. Nonetheless, some 7% of the species are classified as being under some level of threat, ranging from endangered to further protection desirable.

The Martinique oriole (Icterus bonana) is Vulnerable, and Forbes's blackbird (Curaeus forbesi) is listed as Critically Endangered. The oriole is endemic on the West Indian island of Martinique where it was originally distributed throughout the forested areas of the island at lower elevations. The principal threat to this species is brood-parasitism from the shiny cowbird, which colonized the island during the late 1940s and is increasing in abundance. Today, about 75% of the nests are parasitized by cowbirds. Forbe's blackbird is known with certainty from only two regions near the Atlantic coast of Brazil. In the 1880s, when this species was first described, it was said to be local in occurrence, but apparently common where found; however, they are very similar in appearance to the chopi blackbird (Gnorimopsar chopi), so there is some uncertainty about their status because many so-called records of Forbe's blackbirds may have been of chopi blackbirds. Forbe's blackbird is threatened by deforestation and by pressure from parasitism by shiny cowbirds.

The pampas meadowlark (Sturnella defilippii) is Vulnerable, and the Baudó oropendola (Psarocolius cassini) and redbellied grackle (Hypopyrrhus pyrohypogaster) are listed as Endangered. The meadowlark was apparently always rare in Uruguay and Brazil, but was formerly common in central-eastern Argentina. Today, however, cultivation and over-grazing has resulted in a serious decline in their numbers. The red-bellied grackle is endemic to the Andes of Colombia. Although in the past these were not uncommon birds in humid tropical forests, habitat destruction has led to declines in numbers, and today they are local in distribution, although common in a few sites. The saffron-cowled blackbird (Xanthopsar flavus) is a Vulnerable bird of moist grasslands, marshes, agricultural fields, and dry bushy areas of southern Brazil, Paraguay, eastern Argentina, and Uruguay. For reasons that are not well known, but include habitat destruction, their numbers have declined sharply in the last century, especially since the 1970s. The selva cacique (Cacicus koepckeae) is Vulnerable as well. This cacique is known only from the type-locality (the site where it was first collected), in the lowlands of Peru, although there are other sight records from Manú National Park in Peru. Little is known of their biology, but they are probably extremely rare. Although only seven of the approximately 103 species of blackbirds are listed, three of these represent monotypic genera (that is, they are the only species in that genus). In other words, if those three species were to go extinct, three of 25 genera, or approximately 12%, would be lost, leading to a fairly substantial loss of the diversity that has evolved in the Icteridae.

Significance to humans

Many North American blackbirds are considered agricultural pests in many areas where flocks of them descend to feed in grain fields (rice, corn) or feed lots, and thus compete with humans and their livestock for food. As well, they often congregate in immense flocks in migration and winter, and when these flocks gather in densely inhabited areas—as they frequently do—concern is often expressed that they could constitute a threat to human health. Additionally, many people find the noise associated with a blackbird flock to be unpleasant and the excrement unaesthetic, particularly when they are roosting in a city park. Consequently, there is often pressure on government and game officials for mass extermination, and millions have been destroyed.

New World blackbirds have also played an important part in biological research, in part because many are common, conspicuous, and easily observed, and in part because of the great diversity of lifestyles and behaviors represented in the family. Therefore, they have been important subjects of many major studies of behavior, breeding biology, mating systems, and ecology. In North America, studies of the yellow-headed and red-winged blackbirds have been important in the development and testing of theories about territoriality and mating systems of birds, and the paternity of young. These studies have helped to answer many general questions in biology.

Species accounts

Resources

American Ornithologists' Union. Check-list of North American Birds. 7th ed. Washington, DC: American Ornithologists' Union, 1998.

Collar, N.J., L.P. Gonzaga, N. Krabbe, A. Madroño Nieto, L.G. Naranjo, T.A. Parker III, and D.C. Wege. Threatened Birds of the Americas. Cambridge, United Kingdom: International Council for Bird Preservation, 1992.

Jaramillo, A., and P. Burke. New World Blackbirds: The Icterids. Princeton: Princeton University Press, 1999.

Orians, G. Blackbirds of the Americas. Seattle: University of Washington Press, 1985.

Lanyon, S.M. "Polyphyly of the Blackbird Genus Agelaius and the Importance of Assumptions of Monophyly in Comparative Studies." Evolution 10 (1994): 679–693.

Nero, R.W. "A Behavior Study of the Red-Winged Blackbird I: Mating and Nesting Activities." Wilson Bulletin 68 (1956): 4–37.

Johnson, K.P., and S.M. Lanyon. "Molecular Systematics of the Grackles and Allies, and the Effect of Additional Sequence (Cyt b and ND2)." Auk 116 (1999): 759–768.

James David Rising, PhD