Mockingbirds, Thrashers, Tremblers and Catbirds
The members of Family Mimidae, Order Passeriformes, are New World’s species, occupying large parts of North, Central and South America.
The name Mimidae comes from their wide repertoire of sounds, and especially their ability to mimic numerous birds’ songs and other external sounds.
We have two main genera in this family, Mimus and Toxostoma.
Mimus includes fourteen species of mockingbirds. Among them, the Northern Mockingbird (Mimus polyglottos) of North America, and Tropical Mockingbird (Mimus gilvus) extending from S Mexico and the Caribbean, to N and E South America.
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Jean Michel Fenerole
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HANDBOOK OF THE BIRDS OF THE WORLD Vol 10 by Josep del Hoyo-Andrew Elliott-David Christie - Lynx Edicions - ISBN: 8487334725
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Six other Mimus species occur in South America where this genus is the only representative of this family.
We can find the Long-tailed Mockingbird (Mimus longicaudatus) and the Chilean Mockingbird (Mimus thenca). Both have large size and black malar stripes and range west of the Andes.
On the other hand, we find four other Mimus species east of the Andes, lacking the black moustaches. These four mockingbirds frequent mainly open, scrub or desert areas, except the Chalk-browed Mockingbird (Mimus saturninus) which has wide range in E south America with isolated populations in savannahs and non-forested areas in lower Amazonia regions.
The second important genus with ten species is Toxostoma, including the thrashers. They occur in the arid areas of south-western USA and north-western Mexico. Among them, some species such as the California Thrasher (T. redivivum), the Crissal Thrasher (T. crissale) and Le Conte’s Thrasher (T. lecontei) shows plain breast and long bill.
The other species have spotted breast and less curved bill.
The genus Oreoscoptes has a single species, the Sage Thrasher (Oreoscoptes montanus), is found in the Great basin, and is closer to Mimus than Toxostoma.
The two catbirds of Dumetella and Melanoptila genera occur in northern and eastern temperate distribution.
The two species of Melanotis, the Blue Mockingbird (M. caerulescens) and the Blue-and-white Mockingbird (M. hypoleucus) are typically found in tropical and subtropical scrub and edge habitats in Mexico.
The remaining genera are island species. We find them both on East and West coasts. The genus Margarops ranges in the Caribbean, Bahamas, Greater and Lesser Antilles, and on South American islands (off the north coast of Venezuela).
The genus Allenia is restricted to the Lesser Antilles.
The genera Cinclocerthia and Ramphocinclus are restricted to the Lesser Antilles.
We also find two genera on Pacific islands, one in Socorro Island off the west coast of Mexico, and the other on the Galapagos Islands, west of Ecuador. Both are derivatives of mainland Mimus species.
A large majority of the species are resident. They may be sedentary or perform local post-breeding movements. Some northern birds such as the Grey Catbird migrate southwards in winter, to the Gulf of Mexico and Central America, or to the Greater Antilles. Some vagrants have been recorded in Colombia. This species has the longest migration of any mimids with several birds coming from the extreme north-east in Nova Scotia. The Grey Catbird has reached Europe on at least five occasions. One bird was found in North Wales and another on Tenerife, in the Canary Islands.
All the Mimidae are morphologically homogeneous in appearance.
The members of the genera Mimus, Oreoscoptes and Toxostoma are more terrestrial, larger in size and more plainly coloured, whereas the members of genera Melanotis, Dumetella and Melanoptila are more arboreal and smaller. The birds of tropical areas have brighter plumage and pattern.
Most species show little sexual dimorphism. The male may be slightly larger than the female, and have longer wings and tarsus. The juveniles often have streaked pattern on the breast.
There are three exceptions with first the Hood Mockingbird (Mimus macdonaldi) from Española in Galapagos Islands. This one is about 17% heavier than the female. Then, in the Sage Thrasher (Oreoscoptes montanus), the female is 10% larger than the male, as in Grey Catbird (Dumetella carolinensis).
In Caribbean species, the female is larger and has longer bill than male. These “reversed” features also occur in Pearly-eyed Thrasher (Margarops fuscatus) and in Brown Trembler (Cinclocerthia ruficauda).
Most of Mimidae have long legs and tail, and usually long, strong, curved bill. These attributes are characteristic of terrestrial birds. They forage mainly on the ground where the long legs allow the bird to walk and run easily. The long tail, often lowered, is used as balance in ground-foraging birds. The long, curved bill is used for “bill-sweeping” and moved side to side into the leaf-litter. Such bill is also used for picking, probing and digging small holes. These birds are able to displace rocks and fallen branches to find food beneath. In contrast, the long bill is absent in Bendire’s Thrasher (Toxostoma bendirei) and in mainland Mimus species.
Usually, Mimidae have darker upperparts than underparts. The species which have dull plumage often show white markings such as white wings
patches and tail markings. The White-banded Mockingbird (Mimus triurus) is a good example of this feature.
The dullest species may also have various facial markings. The members of genus Melanotis, Mimus of Galápagos and Cinclocerthia of the Caribbean show black ear patches, white lines above the eyes and adjacent black stripes. Several thrashers have white or black malar lines.
The eyes range from black and brown to reddish, orange, yellow and white.
Another feature in some Mimidae is the coloration of the undertail coverts contrasting with upperparts and belly. In the Grey Catbird (Dumetella carolinensis) and in other Toxostoma species, this colour ranges from bright cinnamon-rufous, to tawny-brown and pale buff.
Most of Mimidae are good singers. The songs are loud, penetrating and persistent, with varied pleasant sounds. A single bird can have a large repertoire of notes and phrases, varying according to each species. After studies of the “vocal virtuosity” of the family Mimidae, the Brown Thrasher (Toxostoma rufum) seems to have about 2000 song types.
The repertoire plays an important role in sexual selection, suggesting that males with large repertoire are more attractive for females and able to establish more secure territories.
Numerous species are able to imitate songs and calls of other birds’ species, and include these sounds into their own territorial song.
Other noises such as dog barks, frog calls, whistles, and other sounds may be included too.
The songs consist of succession of phrases often repeated several times. An unusual feature among songbirds, both males and females of several species sing the typical song, such as in California Thrasher and Le Conte’s Thrashers and in Northern Mockingbirds.
Besides their songs, Mimidae are also distinguished by their calls. These loud and conspicuous calls are used to maintain contact between mates within the dense vegetation. The variations on calls may signal either sociable contact or alarm.
The vocal mimicry is widespread in the family. Some birds retain the calls of other summer visitors’ species and mimic them in winter!
Mimus polyglottos leucopterus
All of the mainland Mimidae species of the Americas typically live in low and open scrubby areas, and very occasionally in the undergrowth of low woodland or in savannahs. These birds occupy the more arid parts of the two continents where they frequent various kinds of desert and semi-desert vegetation.
The Grey Catbird, the Northern Mockingbird and the Brown Thrasher prefer woodland edges and scrubby second growth or the riparian vegetation in more open country in the eastern half of the USA.
The South American Clack-browed Mockingbird frequents the same type of habitat including the Amazon Basin.
The island species such as the Cinclocerthia tremblers in Caribbean, and the Galápagos species occupy evergreen tropical forest at high elevations, and the upland moist forest on some islands’ volcanoes.
Several mimids such as the Northern Mockingbird, the Tropical Mockingbird and the South American species occupy suburban parks, gardens and also cultivated areas, and become familiar of populated areas.
Tropical Mockingbird - Mimus gilvus
All these types of habitats provide food such as insects and other invertebrates, many seeds and especially fruits. The diet of Mimidae species varies seasonally and from one locality to another, according to the fruit production. They consume more insects during the breeding season and feed their young with them, whereas seeds and fruits are mainly eaten in autumn and winter.
Insects include beetles, grasshoppers and crickets, ants, bees and wasps, and lepidopteran larvae. They also take spiders, worms and snails.
The Galapagos species take marine arthropods from the shorelines.
They also feed on other animal food including small vertebrates such as lizards, frogs and snakes probably taken in opportunistic fashion.
Several mimids are known to eat the eggs of other species, but not regularly.
The Galapagos Mockingbird has recently documented blood-drinking behaviour. Espanola Mockingbirds were seen to drink blood from beached and injured sea-lions, and from placentas on sea-lion nursery. They also drink blood on marine iguanas from small wounds in their tails. They are egg predators and steal the fish brought to the booby chick by adults. They also may kill and eat the nestling boobies.
Other mockingbirds such as the Scaly-breasted Thrasher in Caribbean woodlands are mainly frugivorous, as the Northern Mockingbird which is able to leave its territory in order to visit fruiting trees.
They take small, soft berries from numerous plants’ species, and the fruits of several cacti, both for the pulp providing them a moisture source in the desert areas, and also for the seeds.
The California and the Brown Thrashers take acorns. They lodge the acorn in a crevice and hammer at the shell. Other mimids consume large, soft fruits, and then they regurgitate the indigestible seeds.
California Thrasher - Toxostoma redivivum
They forage on the ground, searching for arthropods in dense cover and in leaf-litter, performing lateral movements of the bill to displace the litter. They probe and extend the cracks to extract the invertebrates.
The catbirds glean insects from the vegetation. The Caribbean tremblers and the Cinclocerthia and Margarops thrashers are more arboreal.
Usually, the mimids prefer to walk and run instead to fly, and they escape rather by running than by flying from a source of disturbance. Several members of this family nest above the ground and sing from high perches, but they reach them by climbing through the bushes and not by fly. North and South American species do the same.
Thrashers and mockingbirds are highly territorial, and most mimids occupy and defend their areas all year round. Most of them are resident, except the species living at high elevation which perform altitudinal movements.
Song and visual displays are prominent, and advertise the presence of the owner. The pair-members remain mated for long periods and in some cases for many years. Even outside the breeding season, mimids are quite vocal. The monogamous pair occupies the territory and both mates defend it together.
The defence is first by song. Then, aerial displays may accompany these songs, especially in the Mimus species. The flight consists of rising several metres above the perch in looping display-flight, while singing continuously before to return to the perch. These displays expose the white markings of wings and tail. The tail is often cocked or spread, both in flight or while perched, evocative of the bird’s mood.
Mimus polyglottos orpheus - Northern Mockingbird - Mimus polyglottos polyglottos
While feeding on the ground, mockingbirds often engage in “wing-lifting” in order to display the wing markings as signal of presence and possession of the feeding site.
During courtship displays, wing and tail flashing are also used, and the Sage Thrasher performs wing-fluttering displays.
The Brown Trembler performs “wing-trembling”, involving a perched bird drooping the wings repeatedly and quickly. But this behaviour is poorly known, although it occurs frequently in social context.
Many of the larger thrashers often attack and displace other birds’ species such as thrushes, shrikes and large finches, showing great intolerance of other foraging birds in close proximity.
The members of family Mimidae are noisy and aggressive against potential predators, and especially nest predators. Thrashers, mockingbirds and catbirds attack all animals perceived as threat, including snakes and mammals (rats, dogs, cats and squirrels), and even humans. The California Thrasher is able too kill a Western-scrub Jay which is a real nest-robber. Le Conte’s and Curve-billed Thrashers defend strongly their nests against the Greater Roadrunners.
These defence behaviours are accompanied by alarm calls, wing and tail displays, and are performed vigorously.
The members of the family Mimidae have long breeding season, probably involving several broods.
Most of them are monogamous and territorial. Both male and female share the nesting duties, also nest building and nest defence, and they feed the young.
California Thrasher - Toxostoma redivivum
They build a large, rough, open cup of twigs low down in dense vegetation. The interior is lined with softer materials such as grass, rootlets, fur and feathers, moss and plants fibres.
The Sage and Brown Thrashers may sometimes nest on the ground, whereas the arboreal Caribbean tremblers make a domed nest with a side entrance often in a natural cavity. The Pearly-eyed Thrasher nests in caves on Mona Island near Puerto Rico.
The clutch usually contains 3-4 eggs at intermediate latitudes, in deserts or arid areas, but at higher latitudes, the clutches are more important.
The Sage Thrasher lays up to 7 eggs, and the Patagonian Mockingbird up to 6 eggs. The Central American mockingbirds lay 2 eggs and the Caribbean species 2 or 3 eggs.
Incubation usually lasts 12-14 days by both male and female, except the Grey Catbird in which only the female incubates. Young are fed by both parents.
The Galapagos mockingbirds are co-operative breeders, but they lay only 4-5 eggs per clutch. They are strictly territorial, but the territory is occupied by groups of up to 10 or more birds, rather than one pair. They defend collectively the area and take part in nesting duties. The dominant pair is usually monogamous.
In response to the heavy level of nest predation, the chicks grow and fledge quickly, leaving the nest about two weeks after hatching, but before they can fly.
The open nests are vulnerable to predation by snakes, corvids, tree and ground squirrels. On islands, raptors and introduced cats, foxes and racoons kill and eat the chicks.
Mimids perform threat displays and are extremely pugnacious in defending the nest.
These birds are sensitive to disturbances such as off-road traffic, degradation and reduction of the habitat, development for tourism, conversion of scrubby forest to coconut plantations, depending on the region, mainland or on islands.
Mimus polyglottos leucopterus
The island populations are vulnerable to hurricanes which have a massive effect on the species’ numbers and sheep grazing destroys the habitat.
Some species are listed as globally threatened or near threatened at different levels. However, as most of mimids is living in unsuitable areas for agriculture, these birds escaped the negative effects of clearance and fragmentation, in spite of human actions which have accelerated and pushed endemic species close to the brink.
Chalk-browed Mockingbird - Mimus saturninus