Common Scale-backed Antbird Willisornis poecilinotus Scientific name definitions

Common Scale-backed Antbird is a medium-sized, short-tailed antbird of the understory of humid lowland forest. This species is common and widespread throughout Amazonia, except for eastern Brazil south of the Amazon, where it is replaced by its sister species, Xingu Scale-backed Antbird (Willisornis vidua). The head, upper back, and underparts of the male all are pale gray; the lower back is black, each feather with a broad white tip, forming the "scaled" pattern. The wings and tail also are black and white; in one subspecies, the throat and upper breast are black as well. Geographic variation is more extreme in the case of the female: across the five subspecies, the back of the female may be scaled like the male or uniformly brown, and the underparts may be buffy brown or gray. Common Scale-backed Antbird is not an obligate follower of army ants, but it regularly attends these swarms, where it feeds on insects and small vertebrates that are attempting to escape the ants.

12–13 cm; 15·7–19·4 g (nominate), 15·8–20·5 g (duidae), 15–22·3 g (griseiventris). Interscapular patch white. Male nominate race is grey, paler below; lower back patchily black, edged white; wings and tail black, tertials edged white, wing-coverts broadly tipped white, tail spotted and tipped white. Female has crown and sides of head reddish yellow-brown, upperparts olive-brown, lower back patchily brownish black, edged buff; wings as male except remiges blackish brown, edged reddish brown, covert tips pale buff, tail dark olive-brown with white spots, blackish subterminal band; throat pale greyish white, underparts grey, flanks tinged reddish yellow-brown. Juvenile (fledgling) blackish-grey, tail spotted white, wing-coverts tipped pale brownish white. Races vary substantially in plumage, differing from nominate as follows: duidae female has posterior upperparts black with broad white edges, ground colour of tail black, underparts reddish yellow-brown, belly centre cinnamon-rufous, flanks tinged olive-brown; <em>lepidonota</em> female resembles previous but duller , somewhat paler, crown browner, belly centre light buff; gutturalis male has black throat, female resembles last but belly centre pale olive; and <em>griseiventris</em> female lacks black and white on posterior upperparts , has head-sides rufous-buff, throat pale grey and underparts grey.

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• Common x Xingu Scale-backed Antbird (hybrid) Willisornis poecilinotus x vidua

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.

Understorey of humid lowland and foothill evergreen forest, at least locally to 1350 m, e.g. in E Peru. Primarily in terra firme forest, less commonly in várzea/igapó.

Feeds on variety of insects and other arthropods; at least occasionally, also small lizards. In Brazil, nominate race near Manaus observed to prey on ant larvae (Formicidae), cockroaches (Blattidae), grasshoppers (Acrididae), spiders, centipedes (Chilopoda), caterpillars and a gecko, up to 3·5 cm long; in Amapá, also Brazil, stomach contents included beetles, ants, orthopterans, hymenopterans, Blattariae, homopterans, harvestmen and an unidentified vertebrate; stomach contents (n = 18) from SW Venezuela exclusively insects, including beetles, roaches and ants. Other recorded prey include cicadas (Cicadidae), winged ants. Largest prey taken are c. 3–5 cm in length. Pair-members, individuals or family groups forage mostly below 1 m, sometimes to 3 m, very rarely to 5 m; may be regular participant in mixed-species flocks in some areas, but seldom associates with such flocks in most regions, although often in vicinity of other species at army-ant swarms. Regularly follows army ants (Eciton burchelli, Labidus praedator), but seldom beyond its territorial boundaries, and just as frequently forages away from ants. Adeptly clings laterally to both slender and thick (more than 4 cm) vertical saplings, often pausing on single perch for some time while scanning, then making quick, darting sally to seize prey from the ground or, less commonly, from foliage, vines, branches, dead-leaf clusters or trunks; sometimes remains on ground and probes briefly in leaf litter with its bill; regularly lowers tail slowly, then rapidly flicks it upwards to 20 degrees or more above plane of body before lowering it once more. Away from army ants, often remains in relatively small area for long periods; once observed foraging in single patch of undergrowth for almost c. 1 hour. Often arrives at ant swarms at dawn, searching and singing first at sites of ant bivouacs or raiding paths from the previous afternoon; regularly visits statary colonies of ants (usually poorly attended by larger antbirds); wandering subadults may follow ants even more regularly than do territorial adults. When foraging over army ants, mostly wanders around periphery, ceding swarm centre to larger, more dominant obligate ant-followers, even being displaced or supplanted by some non-professional followers such as Myrmoborus myotherinus; frequently forages over small branch raids or ahead of swarms, and race lepidonota sometimes noted as following ant probes up trees to heights of 8 m. Over ants, clings patiently for up to c. 7 minutes on a vertical perch, occasionally pivoting, or reversing its orientation; most attack manoeuvres are short (to 0·5 m, occasionally to 2 m) darting sallies to the ground (69% of 213 attacks in one study) to seize prey with quick stab of the bill, followed by quick jump or flight back up to a perch before ants can counter-attack; also sallies to vines, branches, trunks or foliage, or perch-gleans prey from these surfaces by reaching out, up or down; sometimes tosses leaves with its bill to uncover prey hiding in litter. Small items consumed immediately; larger prey often carried away some distance and dissected, seemingly to avoid being robbed by larger competitors; legs of large prey often eaten first.

Loudsong of nominate race a series (e.g., ten notes, 7·1 seconds) of long upslurred notes (up to 15, occasionally as few as three) with little space between them, each note rising in pitch and gaining in intensity, except final note or notes that decrease in intensity, great individual variation in length and in extent to which final notes rise, and also some geographical variation, with first note of loudsong of nominate race consistently higher-pitched than that in race duidae, while loudsong of latter differs from that of race lepidonotus in being delivered at slower pace and with notes at lower frequencies, and initial notes of griseiventris loudsongs in general are lower-pitched than equivalent notes of lepidonotus, but loudsongs of westernmost population of griseiventris, nearest the range of lepidonotus, are highest in frequency and closest to notes of lepidonotus, suggesting a cline in this character. Calls include sharp “psit” (of varying length, longest in nominate, duidae and lowland lepidonotus, and shortest in highland lepidonotus and griseiventris), a usually descending “chirr”, more abrupt chitter, short whistle quickly repeated 3–4 times, also a longer whistle that falls and then rises in pitch, sounding like “cherri” and typically repeated 3–4 times. Some of these other calls may also vary geographically, but insufficient data are currently available to make robust comparisons.

Season Nov–Mar in French Guiana; nests found in Aug and Apr in Colombia (Meta); season probably Dec–Jul in E Ecuador (based on gonadal condition of females and sightings of fledglings or juveniles) and females in breeding condition in extreme SW Venezuela in Feb–Mar; in Brazil, nest records and observations of fledglings and dependent juveniles suggest season at least Mar–Dec, and possibly in all months (based on moult condition of specimens), with possible peaks in Jun–Jul and Oct–Mar near Manaus; female in Suriname had fully developed but still shell-less egg on 24 Feb. A nest in French Guiana (nominate race) was 85 cm above ground, placed 40 cm down in a cavity, internal diameter 9 cm, lined with dead leaves and some Marasmius fibres, while another of nominate race in Brazil (Manaus) was c. 0·5 m from the base inside a hollow 1·5 m-tall, dead arborescent palm stump of c. 10 cm diameter; an Aug nest in Colombia (either duidae or lepidonota) was cup-shaped, placed c. 50 cm up among bases of leaves of an understorey palm, and an Apr one in same locality (in Meta) was an open cup 11·5 cm × 9·5 cm, constructed of dry fibres and parts of dry palm leaves, placed in natural cavity 8·2 cm × 5·3 cm and 11·5 cm deep, with the cavity wider inside than at entrance and deeper than base of nest, full of decomposing leaves, entrance partially covered by ferns and other understorey plants, 22 cm above ground in live tree; in Ecuador (lepidonota), one nest a small cup of dried grasses, built on ground. Normal clutch two eggs , pinkish to purplish, streaked and spotted with dark red, mauve or purple, size 22·9–23·3 mm × 16·1–16·4 mm, mass c. 3·5 g (nominate) or 19–19·1 mm × 14·7–15·2 mm (either duidae or lepidonota); incubation by both adults, probably only by female at night; both also brood and feed nestlings, which hatch naked with greyish skin above, reddish below, and yellow bills; male cares exclusively for one fledgling, female for other, with the fledglings following adults for at least 1–2 months.

Not globally threatened (Least Concern). Fairly common throughout its extensive range. This includes numerous large protected areas, examples of which are: Brownsberg Nature Park and Raleigh Falls-Voltzberg National Park, in Suriname; Iwokrama Forest Reserve, in Guyana; Canaíma, Yapacana, Duida and La Neblina National Parks and the Alto Orinoco-Casiquiare Biosphere Reserve, in Venezuela; Jaú, Montanhas do Tumucumaque, Pacaás-Novos, and Serra do Divisor National Parks, as well as the Ducke Reserve, in Brazil; Chiribiquete and Tinigua National Parks, in Colombia; Yasuní National Park, in Ecuador; Manu National Park and Biosphere Reserve and Tambopata-Candamo Reserved Zone, in Peru; and Madidi and Noel Kempff Mercado National Parks, in Bolivia. Regions occupied by this species also encompass extensive intact habitat which, although not formally protected, seems to be at little near-term risk. Continued protection of existing parks and reserves should ensure the long-term viability of this thamnophilid.