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Gray Catbird, Northern Mockingbird, and Brown Thrasher

Wildlife Note

Birding and Bird Conservation

________________________________________________________________________________ Gray Catbird, Northern Mockingbird, and Brown Thrasher (PDF)

These three species are among the most vocal of our birds. All belong to Family Mimidae, the "mimic thrushes" or "mimids," and they often imitate the calls of other species, stringing these remembered vocalizations into long, variable songs. Family Mimidae has more than 30 species, which are found only in the New World, with most inhabiting the tropics. The mimids have long tails and short, rounded wings. The three species in the Northeast are solitary (living singly, in pairs, and in family groups rather than in flocks), feed mainly on the ground and in shrubs, and generally eat insects in summer and fruits in winter. The sexes look alike. Adults are preyed on by owls, hawks, foxes, and house cats, and their nests may be raided by snakes, blue jays, crows, grackles, raccoons, opossums, and squirrels.

Gray Catbird (Dumetella carolinensis)—The gray catbird is 8 to 9 inches long, smaller and slenderer than a robin, an overall dark gray with a black cap and chestnut around the vent. Individuals often jerk their tails up, down, and in circles. The species is named for its mewling call, although catbirds also deliver other sounds. They migrate between breeding grounds in the eastern two-thirds of North America and wintering areas in the coastal Southeast and Central America. Gray catbirds are abundant and statewide in Pennsylvania, inhabiting hedgerows, woods undergrowth, regenerating cut-over land, shrubby areas near water, woods edges, and suburban plantings. They shun dense forests.

Catbirds eat wild fruits and insects. In summer the diet is around 60% fruit, and in spring, 20% fruit. Beetles, ants, caterpillars, grasshoppers, crickets, and other insects are common foodstuffs. Catbirds often forage on the ground, using their bills to flick aside leaves and twigs while searching for insects.

Although not as talkative as the northern mockingbird, the catbird is still a versatile vocalizer. Its ability comes in part from the structure of its syrinx, or voice box, with two sides that can operate independently, letting the bird sing with two voices at the same time. A catbird calls out a rapid string of syllables—more than 100 types in some individuals—including squeaks, chitters, whistles, whines, and songs swiped from other birds. The babble, which lasts up to 10 minutes, is frequently punctuated by the familiar catlike mew.

Catbirds are monogamous. They nest from May into July and usually raise two broods per year. The nest, substantial and deeply cupped, is placed in a dense thicket, briar patch, vine tangle, or shrubby tree, 3 to 9 feet above the ground. The female lays three to five eggs, which are a dark greenish-blue and unmarked. Brown-headed cowbirds often lay their eggs in catbird nests, but catbirds almost always recognize the parasitic eggs (which are pale and dotted with brown) and pitch them out of the nest. Catbirds destroy eggs and nestlings of other species, including wood-pewees, robins, and sparrows; biologists don't know whether this behavior represents an attack on competitors or a feeding strategy. Parents feed their own young mainly on insects and spiders. Incubation takes two weeks, and the young leave the nest ten or eleven days after hatching.

Northern Mockingbird (Mimus polyqglottos)—The slender, robin-size northern mockingbird has a gray back, a pale breast and conspicuous white patches on the tail and wings: when foraging, a mockingbird will often stop and flick its wings, opening them to expose the white patches. The species lives year-round on its range, which overlays most of the lower 48 states and includes southern Canada, the Caribbean islands and Mexico. Mockingbirds live in towns and cities, where they often forage on lawns and in thickets, road margins, woods edges, cut-over lands, and farms. They like a mix of low shrubs and open terrain. In Pennsylvania mockingbirds are most common in the southeast, the southcentral (although not in the mountains) and the southwestern regions.

About half of the diet consists of insects and half of native and cultivated fruits. When hunting for insects, a mockingbird will run along on the ground in short grass, stopping and lunging for its prey: beetles, ants, bees, wasps, grasshoppers, and others. Mockingbirds also eat spiders, earthworms, snails, and sowbugs. In fall and winter, berries and fruits make up most of the diet including grapes, apples, barberries, hawthorn, elderberries, and (a particular favorite) multiflora rose hips. Mockingbirds sometimes drive off cedar waxwings and other birds, with whom they compete for fruit. In winter mockingbirds may visit feeding stations for seeds and suet, pugnaciously chasing other birds away.

Both male and female mockingbirds sing, but the males are the true virtuosos. They mimic snatches of other birds' songs, calls of crickets and frogs, dogs barking and mechanical noises like squeaky hinges and squealing tires. A male's repertoire increases as the bird ages and may ultimately include more than 150 distinct song types. Usually an individual repeats one sound or song three to six or more times, then switches to another song, and so on, singing for minutes on end. (Brown thrashers usually repeat each song once, while catbirds do not repeat.) In the spring, male mockingbirds sing to establish territories and attract mates, starting in around an hour before sunrise. They sing in flight, on the ground, from perches, when building nest foundations, during and after copulation, while foraging--even with food clutched in their bills. Unmated males may sing during the night, usually from a hidden perch. Mockingbirds sing from March to August (during the breeding season) and from late September into November (while establishing fall and winter feeding territories).

Mockingbirds are mainly monogamous. Courting males and females chase each other in flight. The nest is a bulky cup built in a dense shrub or a tree, usually three to 10 feet above the ground. The female lays three or four greenish to bluish gray eggs, blotched with brown. She incubates them 12 to 13 days. Both sexes feed the young, which fledge after 12 days, although they're not strong fliers for another week. At fledging, the male may continue to feed the young while the female lays and begins incubating the next clutch. This division of labor lets mockingbirds produce two and sometimes three broods (up to four in the South) during each breeding season. Mockingbirds aggressively defend their nests, driving away predators and attacking humans who venture too close.

Some mockingbirds spend the whole year as a pair on a single territory, while others, particularly in the northern part of the range, use different breeding and wintering territories. In the north, some individuals may migrate south in winter. Young disperse up to 200 miles from where they hatched. Ornithologists believe the spread of multiflora rose (an invasive species once planted widely for wildlife habitat) and the planting of ornamental shrubs (especially Pvracantha, or fire thorn) provided key winter food and shelter, aiding the mockingbird in a northward population expansion that has gone on for close to a century.

Brown Thrasher (Toxostoma rufum)--The largest of our three mimids, the brown thrasher has an 11- to 12-inch length, half of which is tail. Plumage is rich reddish brown above, heavily streaked below. The name "thrasher" may come from the bird's habit of thrashing the ground litter, using its long, curved bill to sling aside leaves and dirt while foraging. Brown thrashers breed across the eastern two-thirds of North America, with a range similar to that of the gray catbird. The species nests statewide in Pennsylvania, although it's more common in the southern than the northern counties. Brown thrashers prefer brushy, thorny places, including hedgerows, thickets, forest margins and clearings and old fields overgrown with shrubs. Shyer than catbirds and mockingbirds, they are less likely to live around people, and they often flee into escape cover at the sight of a human.

Brown thrashers feed on insects (more than half the annual diet), berries, small fruits, seeds and nuts, including many acorns. Occasionally they take crayfish, lizards, and small frogs. The best time to observe brown thrashers is in April, before nest building has commenced, when males sing from high, exposed perches to attract mates. The song is full of improvisation and mimicry of other species, including flickers, titmice, cardinals and thrushes; observers have reported over 3,000 song types, the largest repertoire of any North American bird species. The alarm call is a crackling note that may sound like a loud, smacking kiss. After mating, males continue to sing but in a quieter tone. Territories are two to 10 acres.

The nest, hidden in dense, tangled cover, is built mainly of sticks and twigs lined with cleaned rootlets. Thrashers place their nests from one and a half to twenty feet above the ground and occasionally on the ground itself. The female lays four eggs, which are pale blue and freckled with reddish brown. Both parents incubate. The eggs hatch after eleven to fourteen days, and the young leave from the nest nine to thirteen days after hatching. They stay in the vicinity, and their parents bring them food. Two broods per year are usual; some thrashers switch mates between same-season broods. Nesting runs from early May to the end of July in Pennsylvania.

Brown thrashers in southern areas are permanent residents, but most of those breeding in the Northeast leave the region in September and October and take up residence in thickets in the Gulf states. Statewide, the brown thrasher population seems to have decreased by about four percent a year since the mid-1960s, perhaps because of cowbird parasitism, nest predation and the spread of human settlements the growth of old fields into mature woodlands.