Chalk-browed Mockingbird Mimus saturninus Scientific name definitions

The Chalk-browed Mockingbird is common in open habitats in eastern South America, at least as long as a few trees are present. It is an adaptable species, often found in parks and gardens, and in parts of South America its range is expanding as forested areas are cleared. Like other mockingbirds, it has a loud, varied song, and most often forages on the ground.

23·5–26 cm; 55–73 g. One of the largest Mimus species, brownish , with long legs, long graduated tail  held semi-erect. Nominate race  has dark crown, conspicuous broad white supercilium, blackish line from lores through eye to top of ear-coverts; upperparts brownish with darker striations, rump more buffish-tinged, upperwing-coverts tipped white (rather obscure white wingbars); flight-feathers and tail blackish, conspicuous white tips on all except central rectrices, outer webs white-sided; white below, breast greyer, sides tinged buffy, flanks faintly streaked darker; iris yellow; bill black; legs blackish. Sexes similar, female slightly smaller than male. Juvenile  is browner than adult, underparts buffier, dark streaks  on breast  . Races exhibit minor variation in body size, bill length and plumage: <em>frater</em> is more brownish above than nominate, with no buff tinge on rump; <em>arenaceus</em> is similar to previous but larger-billed; <em>modulator</em> is also very similar, distinguished by more blackish-brown spotting on crown and upper back, lack of grey suffusion on chest, and flanks with decidedly paler buffy tinge and less conspicuous streaks or even unstreaked.

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Editor's Note: Additional distribution information for this taxon can be found in the 'Subspecies' article above. In the future we will develop a range-wide distribution article.

Broad variety of non-forest habitat: savannas, forest edge, low open woodland, scattered trees in pastures, cerrado bushland in Paraguay and Brazil , also caatinga scrub in Brazil, and palm swamp in Suriname. Common around rural settlements, also urban parks and gardens. Inhabits relictual savannas in lower Amazonia (nominate race) and NE Brazil (arenaceus). Lowlands; to c. 2500 m in Argentina (near Tucumán).

Mostly resident; southern populations (e.g. in SE Brazil) appear to be partially migratory.

Omnivorous ; diet includes insects  , e.g. orthopterans and beetles (Coleoptera), also spiders (Araneae), worms, small fruits, seeds, berries. Larger seeds and stones (or pits) of drupes regurgitated. Occasional predator on eggs and nestlings of other birds. Forages largely on ground.

Loud, varied series of notes, trills, phrases; call note a characteristic, sharp and penetrating “tshrip”, alarm a “snorting sha-sha-sha”. Habitually mimics other species, including Roadside Hawk (Rupornis magnirostris) and American Kestrel (Falco sparverius), but not known for any degree of virtuosity.

Breeds Sept–Jan. Monogamous. Helpers at nest recorded in Brazil and Argentina, in some cases young of previous brood, in other cases verified as unrelated to breeding pair, assist in territorial defence, nest-guarding and brood-feeding. Territorial; territory 6–20 ha in very open habitat, less than 1 ha in optimal habitat; defended also against M. gilvus. Nest built over period of 5 days, a loosely constructed, shallow cup, often with old nest used as base, lined with finer materials, placed in crown of low tree, or in dense, often spiny, shrub, 0·5–6·5 m above ground, mostly 1·3–3 m (average 1·9 m at Argentina study site). Clutch 3–4 eggs  , pale greenish-blue with dense reddish-brown spots and blotches, especially at larger end; hatching asynchronous; incubation period reported as 12 days in Brazil, also 13–15 days in Argentina; chicks  fed by both parents, also by any helpers present, nestling period 15 days in Brazil, 12–14 days in Argentina; nestlings susceptible to botfly (Philornis) infestation; young fed  by parents  for c. a week out of nest, remain on parental territory through subsequent non-breeding season. Common host of Shiny Cowbird (Molothrus bonariensis), especially in S (c. 80% of nests parasitized); accepts spotted version of dimorphic cowbird eggs, rejects unspotted version.

Not globally threatened. Very common throughout much of range. Occurs in several protected areas, e.g. Serra da Canastra National Park, in Brazil, and Costanera Sur Ecological Reserve, in Argentina. No perceived threats, although nesting losses due to cowbird parasitism are considerable.