Yellow-breasted Warbling-Antbird Hypocnemis subflava Scientific name definitions

One product of the substantial ‘carving up’ of the ‘old’ ‘Warbling Antbird’ was that Yellow-breasted Warbling-Antbird, of southern Peru to west-central Bolivia, and extreme southwest Amazonian Brazil, became one of the more range restricted of the six species of warbling-antbirds now recognized. The adjoining species, Peruvian Warbling-Antbird (Hypocnemis peruviana), is fortunately is easily identified, without recourse to a knowledge of vocalizations, as it is white-, rather than yellow-, breasted. At least in Peru, one of two regions where direct sympatry between these two species has been recorded, they appear to segregate by habitat as well, with Yellow-breasted Warbling-Antbird being found in Guadua bamboo thickets in floodplain forest, whereas Peruvian Warbling-Antbird prefers terra firme forest without bamboo in this area.

12 cm; mean 13·8 g (nominate). Compared to other members of the H. cantator species complex differs in its plain pale yellow throat to belly, very weak rufous flanks, and pale olive-grey versus rufous-toned rump. Nominate race is paler overall, greyer above with broader and heavier black-and-white markings, grey-brown remiges and tail, yellower below, and rear underparts pale buff; race collinsi is very similar, but paler, purer grey with few black-and-white spots above, and female has pale olive-grey upperparts.

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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.

Understorey to midstorey of humid evergreen-forest borders, especially in densely vegetated light-gaps (e.g., around treefalls) and streams within forest, as well as adjacent tall second-growth woodland. Local microhabitat shifts occur, as with at least some other species in the H. cantator complex. Race collinsi restricted to stands of Guadua bamboo in some parts of its range; in Madre de Dios, SE Peru, is especially associated with bamboo and relatively short-stature trees in transitional forest, although it is more abundant in river-edge forest than in transitional forest, and in this region it is absent from terra firme forest, where it is replaced by H. peruviana. Nominate race also regularly uses bamboo for feeding and nesting, but is seemingly able to use other suitable forested habitats where H. peruviana is absent. Recorded to 1600 m in SE Peru (with H. peruviana in same region being generally confined to elevations below c. 300 m).

Most aspects of diet and foraging behaviour probably very similar to those of the formerly conspecific H. cantator (which see). Diet not well known, but young at a nest in SE Peru were provisioned with butterflies, crickets, caterpillars, beetles and spiders. In SE Peru, both live leaves and bamboo leaves are the most frequently used substrates for foraging in both river-edge and transitional forests, but suspended dead leaves are investigated much more frequently in the former type, with 20% of all observed foraging manoeuvres targeted at dead leaves (versus < 10% in transitional forest) and mean foraging height above ground tends to be marginally lower (3·5 m, versus 4·1 m in transitional forest); another study from same region classified the species as an “occasional user” of dead leaves.

For general characteristics of male and female loudsongs, plus calls, see relevant section of account for H. cantator. Decelerating loudsong generally very similar to, if not indistinguishable from, that of H. peruviana, e.g. “chee-cher-CHEER-cheer-cher-chrrr”, although it has been suggested that, on average, it has more noticeable inter-note intervals and often lacks the harsh terminal notes of the other species; on average, that of male is also characterised in being very marginally longer with more notes and faster overall pace. Calls include a low-pitched series of two (rarely three) broad-band raspy notes, “hrjzz hrjzzesh”, quite like “chirr” calls of other species in the complex, but always given in pairs or triplets (“chirr” calls delivered more erratically) and of longer duration, with level of frequency either even or drifting upwards (“chirr” calls usually drift down). Like other closely related taxa, both sexes also give “chit” calls, at least in race collinsi always clear notes with an apparent harmonic, thus quite different from those of other members of the H. cantator species group. Both sexes sing and call consistently year-round, with higher rates of singing in males than females, peak loudsongs around dawn and calls peaking later in the morning.

Eight nests have been found, all in SE Peru (Cuzco and Madre de Dios) in Aug–Dec, differing in shape from those of H. cantator and H. peruviana, being deep pouch-shaped cups with mean outer dimensions of c. 78 mm by 74 mm and 89 mm high and the cup measured c. 53 mm wide by 52 mm deep, woven with dead palm fronds, bamboo (Guadua) leaves (in one nest), dead leaves and green moss, with lining of dry grass fibres and dark rootlets, placed 0·3–1·8 m above ground in dense understorey vegetation of ferns and shrubs, usually near streams, being specifically attached to branch forks of seedlings. However, a the one nest of race collinsi was described as cup-shaped, 10 cm in diameter, 10 cm deep, woven with dead palm fronds, dead leaves and green moss, and placed 25 cm above ground. Clutch two white eggs with highly variable brownish-red (race collinsi) or maroon (nominate) specks and streaks, the second laid two days after first, mean size 20·2 mm × 14·2 mm, mass 2·1 g; incubated by both adults in comparatively long stints of on average c. 1·5 hours (longest session 480 minutes by day, but female might incubate for up to 16 hours during afternoon and night), but overall period unknown. Young hatch naked with pinkish skin, yellow gape and feet, weight on day two 2·3 g and fledge after 11 days (at one nest) at mass 11·8 g, being provisioned and brooded by both adults during nestling period, with rates of feeding increasing, from c. 2 times per hour during first three days, to almost five times per hour on days 4–5 and to more than seven times per hour in final stages. Of seven nests with known outcomes, six failed, all as a result of predation. Lifespan unknown, but one adult male retrapped five years after first being caught, still on same territory.

Not globally threatened (Least Concern). Fairly common to common throughout most of its extensive range, e.g. in E Acre (Brazil), where it was only recently (since 1997) discovered and where it appears to replace H. hypoxantha geographically, with the latter being apparently restricted to W Acre. Known from a number of protected areas including Madidi National Park, in Bolivia, the Reserva Extrativista Chico Mendes and Catuaba Reserve, in Brazil, and Manu Biosphere Reserve and Tambopata-Candamo Reserved Zone, in Peru.