Thrashers and mockingbirds

(Mimidae)

Class Aves

Order Passeriformes

Suborder Passeri

Family Mimidae

Thumbnail description
Medium-sized songbirds, usually with long graduated tails and rounded wings, and long, often decurved bills; frequently with loud, varied, and sometimes imitative, songs

Size
8.2–12.2 in (20.5–30.5 cm)

Number of genera, species
10 genera; 35 species

Habitat
Forest edges, scrubland, suburban areas and abandoned farmland, desert scrub, and waterless desert

Conservation status
Critically Endangered: 2 species; Endangered: 2 species; Near Threatened: 2 species

Distribution
North America from southern Canada south, through Central America and West Indies south to Patagonia; Galápagos Islands, Bermuda

Evolution and systematics

The mimids (a collective term which covers mockingbirds, thrashers, catbirds, and tremblers) are a group of New World oscine passerines with many common structural features. The relationships of this group to other passerine families has been the subject of some debate over the years. Originally they were considered to be closest to the thrushes, a family that breeds on every continent except Antarctica (indeed, Linnaeus, in 1758, put both the brown thrasher [Toxostoma rufum] and the northern mockingbird [Mimus polyglottos] in the same genus as the Eurasian blackbird [Turdus merula]); however, recent work based on DNA hybridization studies suggests that mimids are a sister-group to the starlings (Sturnidae), an exclusively Old World family. The geographic origin of the mimids is clearly New World, since they occur nowhere else, but exactly where in the Americas is less clear. The greatest diversity of breeding species of mimids is found in the southwestern United States and Mexico. South America, the continent richest in bird species, has only seven mimids, all rather similar members of the one genus Mimus, arguing for a relatively recent colonization with little time for widely divergent evolution into the different habitats found in South America. By contrast, the West Indies has eight species. Some have clearly been there for a substantial time, since they are members of three very diverse genera endemic to the region. Based purely on considerations of species abundance and diversity, an origin in Central America is argued for, with an early colonization of the West Indies and a later invasion of South America. This remains speculative in the absence of hard evidence, since the fossil record is unhelpful.

Physical characteristics

The 35 species of mimid (Peter's checklist lists 13 genera and 31 species, but a more recent classification is used here) share many common characteristics. All are, for passerines, quite large, typically of a size similar to a Eurasian blackbird (Turdus merula) or American robin (Turdus migratorius). Legs and feet tend to be stout and sturdy, the tail long and graduated, the wings generally rather short and rounded. The bill is always relatively large, sometimes long and decurved. Coloration is usually fairly muted; most species are various shades of gray or brown (often brightly rufous), or in some cases

blue. Bright greens, yellows, and reds are absent, although in several species the irides are a startling red or orange. Sexes are similar. The two largest groups within the Mimidae are the thrashers, genus Toxostoma, with 11 or 12 (according to accepted taxonomy) species, and the mockingbirds, genus Mimus, with 9 or 10 species. Thrashers tend to be heavy, often largely terrestrial species, sometimes heavily spotted below, with strong and often markedly decurved bills. In plumage, mockingbirds tend to be various shades of gray, often with conspicuous white flashes on wings and tail; the bill is more thrush-like, not strongly decurved. A closely allied genus, Nesomimus, is endemic to the Galápagos Islands; the four species are very similar, a generally brown-gray plumage with darker markings. Catbirds comprise two species; one, highly migratory, occurs all over eastern North America, the second, sedentary, is confined to Guatemala, Belize, and the Yucatán Peninsula of Mexico.

The greatest diversity of physical form is found in the West Indies where there are several unique island forms. The bizarre tremblers, found only in the Lesser Antilles, are the most aberrant mimids, with a fine, decurved bill (longer in the female) and an extraordinary habit of shaking and trembling the wings. Also endemic to the Lesser Antilles (two islands only) is the striking and endangered white-breasted thrasher (Ramphocinclus brachyurus,) with blackish upperparts, white underparts, and a red eye.

Distribution

Mimids are exclusively a New World family, apart from vagrant records of three migratory North American species in Europe. Mimids occupy most of North and South America, being absent only from the boreal forest and tundra regions of North America (Newfoundland, Labrador, and the northern sections of the Canadian provinces across to Alaska), the Falkland Islands and extreme southern South America, and as breeding species, some parts of Central America. Mimids occur throughout the West Indies, Bermuda, and the Galápagos Islands. The greatest species diversity occurs in the southwestern United States and adjacent Mexico, but the largest generic diversity is found in the Caribbean, where there are a number of endemic, highly restricted genera. The mimids found throughout much of mainland South America are all closely related and very similar members of the genus Mimus. The Galápagos is home to a genus, Nesomimus, closely related to Mimus.

Habitat

The habitats required by mimids are varied, but essentially involve bushland. Apart from some West Indian species, they are absent from dense forest (though found in forest edge) and from savanna or prairie that lack bush. Within these requirements, habitats are quite diverse, from well-watered bushland in eastern North America (being especially fond of abandoned farmland) to cactus desert in the American Southwest, including some extremely arid zones such as Death Valley in California. Some West Indian species, notably the genus Cinclocerthia, inhabit wet epiphytic rainforest, but the family is generally absent from such habitat-types in South America.

Behavior

Most mimids are not excessively shy and some species are noted for their demonstrative and rambunctious behavior. Many species, especially of the genus Mimus, have exploited very modified habitats and live in comfortable proximity to man in suburban locations. Some others, such as the Crissal thrasher (Toxostoma crissale), an inhabitant of riparian brushland

in the American Southwest, are very secretive, rushing into dense cover at the slightest disturbance. Most members of the family spend much of their time on the ground or in the lower levels of vegetation, even though they may sing from exposed perches. Many species are notably aggressive, not hesitating to harass cats, dogs, or corvids by physical attack.

The songs of most mimids are loud, liquid, and generally very attractive. In some cases, especially the mockingbirds, there are strong imitative elements of other species. Some species sing at night.

Feeding ecology and diet

Mimids typically have long, pointed bills; in many cases these have a pronounced downward curvature and in some species are extremely decurved. Species with especially long curved bills, such as the California thrasher (Toxostoma redivivum), spend much time probing in loose soil. Food is varied; for most species it is predominantly invertebrate, but small frogs, lizards, and crawfish may be taken. Substantial amounts of vegetable matter including berries and seed-pods are taken, especially, in northern species, in fall and winter. The mockingbirds of the Galápagos Islands have developed some extraordinary and unique feeding traits in response to their harsh and variable environment. On islands where there are seabird colonies, such as Hood (Española), the resident species will eat seabird eggs, cracking open eggs of smaller species (such as the swallow-tailed gull, Creagrus furcatus). The more robust eggs of boobies and albatrosses cannot be broken into, but those with cracks are immediately attacked. An even more bizarre food source is blood. Marine mammals such as sea lions, wounded in territorial battles, soon attract groups of mockingbirds, which actively drink blood from open wounds and peck up congealed blood from the ground. One visiting ornithologist recorded that he twice had to fend off mockingbirds that attempted to pick off blood spots from scratches on his legs. Other food sources include ectoparasites (often engorged with blood) and loose skin from marine iguanas (Amblyrhynchus subcristatus), disgorged fish, and other carrion and marine mammal feces. Species found on islands without seabird colonies such as Chatham (San Cristóbal) are more conventional in diet.

Reproductive biology

Most mimid species build open-cup nests, usually situated at heights of 3–6 ft (1–2 m) in bushes. The exceptions are the pearly-eyed thrasher (Margarops fuscatus) of the West Indies, which builds a bulky stick nest in cavities of trees and the two tremblers, found in the Lesser Antilles, whose nests are domed structures with side entrances. Desert species, such as Leconte's thrasher (Toxostoma lecontei), take great care to position their nests in such a way as to take greatest advantage of shade. Egg color is variable within the family; most thrashers (Toxostoma) and mockingbirds (Mimus) lay speckled or spotted eggs, with either a whitish or greenish background, but catbirds (Dumetella and Melanoptila), the Central American blue mockingbird (Melanotis caerulescens), and most of the endemic West Indian genera lay unmarked bluish or greenish eggs. Incubation is generally by both sexes in the thrashers, but by the female alone in mockingbirds and catbirds. In most species breeding is conventional (i.e. one male and one female per nest), but in the mockingbirds of the Galápagos Islands a complex system of social breeding has evolved, with a "territorial group" of birds, which in the case of the Hood mockingbird (Nesomimus macdonaldi) may number up to 40, defending a group territory. Within the group is a set hierarchy, the dominant male being the oldest bird. Up to four breeding females occur in a group,

and non-breeding birds may assist in the rearing of broods of related pairs.

Conservation status

Most species of mimids pose no conservation concerns, and some populations seem to have benefited from human conversions of forest to bushland. However, five species, four of which are island endemics, are the source of serious anxiety. The Socorro mockingbird (Mimodes graysoni), formerly abundant on Socorro Island in the Revillagigedo group west of Mexico is Critically Endangered due to predation by introduced cats and habitat destruction by introduced goats. Rather puzzlingly, the Cozumel thrasher (Toxostoma guttatum) of Cozumel Island off the coast of the Yucatán Peninsula is also Critically Endangered, having suffered catastrophic population declines following hurricanes in 1988 and 1995; curiously none of the other endemic Cozumel species has suffered and all seem as abundant as previously. In the West Indies the two races of white-breasted thrasher, found on St Lucia and Martinique, are both Endangered, possibly critically, with shrinking populations of fewer than 100 pairs each. In these cases the causes seem to be habitat destruction and predation by introduced mongooses. The various species of mockingbirds in the Galápagos Islands seem to be doing quite well, with the exception of the Charles mockingbird (Nesomimus trifasciatus), formerly found on Charles (Floreana) Island, now restricted to two tiny islets off Charles. In this case the culprit appears to be the black rat (Rattus rattus), though other species in the archipelago appear to be able to coexist with this introduced species.

Because of its limited range, the black catbird (Melanoptila glabrirostris) of the Yucatán Peninsula is classified as Near Threatened; it is, however, quite common in several locations. Recent information is lacking on the San Andres mockingbird (Mimus magnirostris), confined to Isla San Andrés (St. Andrew Island) in the western Caribbean; the island has been the subject of much recent development as a resort.

Significance to humans

None of the mimids has great economic significance apart from sporadic reports of damage to berry crops by some species. They do, however, include a number of well-known and very popular species, so much so that the brown thrasher has been adopted as the state bird of Georgia, and the northern mockingbird by no fewer than five southern U.S. states from Tennessee to Texas.

Species accounts

List of Species

Gray catbird

Dumetella carolinensis

taxonomy

Muscicapa carolinensis Linnaeus, 1766, the Carolinas.

other common names

English: (Bermuda) blackbird; French: Moqueur chat; German: Katzendrossel; Spanish: Sinsonte Maullador.

physical characteristics

8.1–8.5 in (20.5–21.5 cm); 0.94–2.0 oz (26.6–56.5 g). Plumage generally dark leaden-gray, crown dull black, crissum deep chestnut-brown. Eye deep brown, bill and legs black.

distribution

Breeds across eastern North America from Nova Scotia to east Texas, west to British Columbia, north New Mexico; Bermuda. Winters from southern New England through southeast states including Florida, coastal Texas, east Mexico through Central America to Panama, Bahamas, Cuba, Jamaica, rarely in Lesser Antilles. Vagrant Colombia, western Europe.

habitat

Scrubland, forest edge, well-vegetated suburban areas, abandoned orchards.

behavior

Usually in lower levels of vegetation. Rather retiring; frequently sings from dense cover. Song is a pleasant series of whistled and gurgled notes, interspersed with harsher notes. Female sometimes sings. Calls include a cat-like mewing and more grating notes.

feeding ecology and diet

Food is varied, including many invertebrates (ants, caterpillars, spiders, grasshoppers) and some vegetable matter, including wild grapes, especially in fall; takes eggs of other small passerine species up to the size of American robin.

reproductive biology

Nest is a cup-shaped construction of fine grasses etc, lined with horsehair and fine materials, built mostly by female, from ground level to 48 ft (15 m), usually about 4–5 ft (1.5 m) up. Eggs three to four, sometimes one to six, bright blue-green. Incubation by female alone, 12–14 days. Young fed by both parents, fledging period 8–12 days. Double-brooded over most of range, triple-brooded in southern areas.

conservation status

Not threatened. Common over much of its range; has probably benefited from clearance of forest and subsequent abandonment of marginal farmland.

significance to humans

No economic significance; a popular and widespread species.

Blue-and-white mockingbird

Melanotis hypoleucus

taxonomy

Melanotis hypoleucus Hartlaub, 1852, Guatemala.

other common names

English: White-breasted blue mockingbird; French: Moqueur bleu et blanc; German: Lazurspottdrossel; Spanish: Sinsonte Matorralejo.

physical characteristics

10–11 in (25.5–28 cm); 2.1–2.3 oz (60–63 g). Upperparts deep blue, underparts white apart from dark blue-gray flanks and vent. Facial mask black. Eyes deep red, bill and legs black. Juvenile dull blackish gray above and below with some white on underparts.

distribution

Southern Mexico (Chiapas), highlands of Guatemala, southern Honduras, northern El Salvador.

habitat

Open pine and oak woodland and scrub with dense understorey, fairly humid at higher altitudes; at lower altitudes drier scrubland. 3,300–9,800 ft (1,000–3,000 m).

behavior

Shy and retiring, usually found in pairs or family parties feeding on or near the ground. Song has a variety of repeated short musical notes, or a medley of whistles and harsher notes.

feeding ecology and diet

Feeds mostly on the ground, sweeping leaf-litter aside with sideways movements of the bill. Food omnivorous; invertebrates, also berries.

reproductive biology

Little known. Nest is a shallow untidy cup of coarse sticks, lined with fibers, placed 3–15 ft (1–5 m) above ground in dense thickets or saplings. Eggs light blue, unmarked, average two at higher altitudes, three at lower altitudes. Incubation by female, period not recorded; young fed by both parents, fledging period 14–15 days.

conservation status

Not threatened. In suitable habitat quite common; susceptible to habitat destruction and now very restricted in some parts of range (e.g., El Salvador).

significance to humans

None known.

Northern mockingbird

Mimus polyglottos

taxonomy

Turdus polyglottos Linnaeus, 1758, Carolina. Three subspecies.

other common names

English: Mockingbird; mocking thrush; French: Moqueur polyglotte; German: Spottdrossel; Spanish: Sinsonte Común.

physical characteristics

9–10 in (23–25.5 cm); 1.3–2 oz (36.2–55.7 g). Plumage generally gray, wings and tail darker gray with pale edgings to coverts, white flash on primaries and white outer rectrices. Eye yellow, bill black with paler base, legs dusky. Juvenile with obscure spots on chest.

distribution

M. p. polyglottos: eastern North America from east Nebraska to Nova Scotia, south to east Texas and Florida; M. p. leucopterus: western North America from northwest Nebraska and west

Texas to the Pacific coast, south throughout Mexico to the Isthmus of Tehuantepec; M. p. orpheus: Bahama Islands, Greater Antilles east to Virgin Is. Vagrant to Great Britain; introduced to Hawaiian Islands.

habitat

Open bushland, well-vegetated suburban areas, abandoned farmland, orchards.

behavior

Self-assured and conspicuous. Spends most of its time on the ground or in low vegetation. During breeding season very aggressive, not hesitating to attack predators such as cats and crows. Song is a loud, very varied series of strong musical notes, frequently including imitations of other species, sometimes repeated over and over; often sings at night, especially in urban settings.

feeding ecology and diet

Food includes both animal (mostly invertebrate, but including small lizards) and vegetable matter (especially berries).

reproductive biology

Nest is an open cup, the base of dead twigs, built mainly by the male, the lining of grasses added by the female, usually less than 10 ft (3 m) from the ground in shrubs. Eggs two to six, base-color bluish or greenish white or somewhat darker, with brownish markings. Incubation by female alone, 12–13 days. Fed by both parents, fledging period 12–15days. Two or three broods per year.

conservation status

Not threatened. Over most of its range common or abundant. Has adapted well to human situations and probably expanded as forest was cleared; has benefited from plantings of such species as multiflora roses.

significance to humans

Little economic significance. A popular species, widely celebrated in literature and the state bird of Texas, Arkansas, Mississippi, Florida, and Tennessee.

Hood mockingbird

Nesomimus macdonaldi

taxonomy

Nesomimus macdonaldi Ridgway, 1890, Hood Island (Isla Española), Galápagos Archipelago.

other common names

French: Moqueur d'Espanola; German: Galapagos-Spottdrossel; Spanish: Sinsonte de los Galápagos.

physical characteristics

11 in (28 cm). Weight not available. Generally variegated dull gray-brown above, off-white below with variable amount of darker spotting on chest. Eye yellow, bill and legs black.

distribution

Confined entirely to Hood Island (Española) in the Galápagos, an island measuring approximately 8 mi long and 4 mi wide (13 by 6.5 km).

habitat

Arid scrub; spends much time in seabird colonies.

behavior

Totally fearless of humans. The mockingbirds of the Galápagos Islands live in groups, defending communal territories; in the Hood mockingbird the groups are larger than in the other species, at times up to 40 individuals. Groups rapidly adopt any temporary human encampment, investigating unfamiliar objects inquisitively and snapping up any offerings found therein.

feeding ecology and diet

Hood is the site of major marine mammal and seabird colonies and the Hood mockingbird, in contrast to species that live on other islands without such colonies, has developed some unique and bizarre feeding habits. The birds will eat blood

from animals' fresh wounds or eat congealed blood from the sand. Engorged ticks and skin are picked from live iguanas. The Hood mockingbird has a more powerful bill than other members of the genus, and uses this to predate the eggs of swallow-tailed gulls (Creagrus furcatus), but larger eggs of boobies and albatrosses are only attacked if already damaged. Other food items include invertebrates, vegetable matter, carrion and feces. Groups whose communal territories do not include a seabird or mammal colony have less varied diets.

reproductive biology

Groups of up to 40 individuals occupy and mutually defend a group territory, intruders being intimidated by consolidated displays of aggression. In less optimal territories (e.g., those without access to colonies), group size is smaller. Little published information on nest and eggs; presumably similar to other species of the genus; the Galapagos mockingbird (N. parvulus) builds a cup-shaped nest in a shrub and lays three to four eggs which are blue-green with brown markings.

conservation status

Not threatened. Within its small range, abundant and not in any obvious hazard. However, introduction of any alien predatory species such as cats would very rapidly change this situation.

significance to humans

Of very great significance with regard to evolutionary and behavioral studies. The Galápagos fauna also has a major economic impact on the finances of Ecuador by virtue of the significant influx of foreign capital from tourism and from visiting zoologists.

Brown thrasher

Toxostoma rufum

taxonomy

Turdus rufus Linnaeus, 1758, Carolina. Two subspecies.

other common names

French: Moqueur roux; German: Rotrücken-Spottdrossel; Spanish: Cuitlacoche Rojizo.

physical characteristics

10–11 in (25.5–28 cm); 2–3.2 oz (57.6–89 g) Upperparts deep rufous-brown, two whitish wing-bars on covert edges, underparts buffy-white with conspicuous blackish tear-drop shaped markings, eye yellow, bill brownish with flesh-colored base, legs brownish.

distribution

T. r .rufum breeds in eastern North America from New Brunswick and Maine south to Florida and west to central Ontario. T. r. longicauda breeds from western Ontario to southern Alberta, south to northeast New Mexico and central Oklahoma. The species winters from coastal Massachusetts to Texas, north to southern Illinois and Indiana. Vagrant to England, Bermuda, northern Alaska, Cuba, Bahamas, and northern Mexico.

habitat

Brushy areas, field-edges with hedges, well-vegetated suburbs, abandoned farmland.

behavior

Not particularly shy. Spends most of its time on or near ground, but frequently sings from high exposed perches. Song

is an attractive series of loud musical phrases, each phrase usually repeated, the whole song often continuing for several minutes at a time.

feeding ecology and diet

Food is very varied; many invertebrates including caterpillars, spiders, grasshoppers, and crayfish, also small frogs, snakes, and lizards; vegetable matter, especially berries, but also acorns, corn etc. Feeds mostly on the ground, probing into soft soil, sweeping aside leaf litter with sideways movements of the bill.

reproductive biology

Nest is a bulky open cup, built of thorny twigs and lined with grass stems etc., located as high as 20 ft (6 m) in trees or bushes, but also frequently on the ground; built by both sexes. Eggs three to five, rarely only two, pale bluish white with fine reddish dots. Incubation by both sexes, 11–14 days; young fed by both sexes. Usually double-brooded.

conservation status

Not threatened. Probably benefited from the spread of agriculture and especially from the abandonment and re-vegetation of marginal cropland. However, recent significant declines in overall population in Ontario and by implication elsewhere.

significance to humans

A popular and well-known species, the state bird of Georgia.

Brown trembler

Cinclocerthia ruficauda

taxonomy

Stenorhynchus ruficauda Gould, 1835. Three subspecies.

other common names

English: Brown bird, gray trembler, (Caribbean) trembling thrush; French: Trembleur brun; German: Zitterdrossel; Spanish: Temblador Castaño.

physical characteristics

9–10 in (23–25.5 m); 1.8 oz (50 g) (average). Upperparts dark olivaceous-brown, with blackish brown crown and rufescent

rump. Underparts dull gray-brown, becoming orange-brown on belly. Eyes light yellow. Bill long, slender and decurved, black; legs brown. Females have longer bill than males; juveniles faintly spotted on chest.

distribution

C. r. ruficauda Dominica, West Indies; C. r. tremula Saba south to Guadeloupe, W.I.; C. r. tenebrosa, St. Vincent, W.I.

habitat

Wet forest with epiphytes, more rarely in grapefruit, cacao, and banana plantations.

behavior

Occurs at all levels from the ground to tree-crowns. Occurs in pairs or small groups. Has peculiar habit of trembling, consisting of drooping both wings then quickly bringing them upwards while jerking the tail nervously. On ground it hops with cocked tail. Song is varied; loud notes uttered at intervals, some rich and warbled, others harsh or squeaky.

feeding ecology and diet

Food very varied; much invertebrate matter including insects, spiders, scorpions, and snails, also small tree-frogs and lizards. Fruit and berries including seedpods. Feeds at all levels; probes into ground and epiphytes with long bill; clings to tree trunks while probing into cavities in the manner of a woodcreeper.

reproductive biology

Nest is a cup of rootlets, lined with finer material, in the base of a palm frond, in a tree cavity, or in a hollow stump; may use nest-boxes. Some nests reported to be domed with a side entrance. Eggs two to three, unmarked greenish blue. Incubation and fledging periods not recorded.

conservation status

Not threatened. On several islands, populations are much reduced due to habitat destruction, but still abundant on Dominica and common on Guadeloupe and Saba. Extinct on St. Eustatius.

significance to humans

None known.

Resources

Books

Bent, A.C. Life Histories of North American Nuthatches, Wrens, Thrashers and their Allies. Bulletin 195, U.S. Nat. Mus. 1948.

Brewer, David, and B.K. MacKay. Wrens, Dippers and Thrashers. London: Christopher Helm; and New Haven: Yale University Press, 2001.

Collar, N.J., L.P. Gonzaga, N. Krabbe, A. Madroño Nieto, L.G. Naranjo, and T.A. Parker. Threatened Birds of the Americas: the ICBP/IUCN Red data Book. Washington, DC: Smithsonian Inst. Press, 1992.

Periodicals

Bowman, R.I., and A. Cartier. "Egg-pecking behaviour in Galápagos mockingbirds." Living Bird 10 (1971): 243–270.

Castellanos, A., and R. Rodriguez-Estrella. "Current status of the Socorro Mockingbird." Wilson Bull. 105 (1993): 167–171.

Curry, R.L., and D.J. Anderson. "Interisland variation in blood-drinking by Galápagos Mockingbirds, Nesomimus parvulus, in a climatically variable environment." Auk 104(1987): 517–521.

Grant, P.R. and N. Grant. "Breeding and feeding of Galápagos Mockingbirds Nesomimus parvulus." Auk 90 (1979): 723–736.

Markowsky, J.K., W. Glanz, and M. Hunter. "Why do Brown Tremblers tremble?" Journal of Field Ornithology 65 (1994): 247–249.

Skutch, A.F. "Life history of the White-breasted Blue Mockingbird" Condor 52 (1950): 220–227.

Zusi, R.L. "Ecology and adaptations of the Trembler on the island of Dominica." The Living Bird, eighth annual of the Cornell Laboratory of Ornithology, (1969): 137–164. Cornell University, Ithaca, NY.

Other

Hardy, J.W., J.C. Barlow, and B.B. Coffey Jr. Voices of all the mockingbirds, thrashers and their allies. Gainesville, FL: ARA Records, 1987.

David Brewer, PhD