Bicolored Antbird Gymnopithys bicolor Scientific name definitions

The Bicolored Antbird is one of three species of Gymnopithys antbirds, and is considered to be an obligate ant-follower. Five subspecies are currently recognized over the species’ relatively wide range, which encompasses Central America from Honduras south to Panama, then through northern Colombia south to western Ecuador. The Bicolored Antbird inhabits the understory of lowland forests, ranging locally into the foothills, and feeds on insects, other arthropods, and small frogs and lizards.

13·5–14·5 cm; 28–37 g. Until recently, generally considered to be conspecific with G. leucaspis, but differs in its browner, less ruddy-chestnut crown and upperparts , upper postocular area dull brown (olivascens) or grey (other taxa), whereas G. leucopsis has a completely chestnut cap, and black as opposed to white malar area. Races differ as follows: nominate has forehead and postocular area blue-grey, lores and subocular area black, wing and tail edgings more reddish yellow-brown, band from lower neck side to flanks brown (not blackish), blue periorbital area more dusky, female with no cinnamon interscapular patch; daguae is similar to previous but darker; <em>aequatorialis</em> is darker than last, forehead rufous, sides blacker; olivascens resembles previous, but forehead and postocular area brown like crown, upperparts tinged olive; ruficeps differs from previous in brighter rufous forehead and crown, blackish postocular area (small area of grey at rear ear-coverts), darker and more rufescent back, more rufescent band on side.

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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 of humid lowland and foothill evergreen forest (primarily terra firme) and adjacent mature second-growth woodland; mostly below 900 m, locally higher, to 1500 m in Panama and 1700 m in Costa Rica.

Feeds on insects and other arthropods, particularly orthopterans and spiders; less frequently on small frogs and lizards. Recorded arthropod prey include cockroaches (Blattidae), crickets (Gryllidae), grasshoppers (Acrididae), katydids (Tettigoniidae), hemipterans, beetles (Coleoptera), earwigs (Dermaptera), hymenopterans, lepidopterans, spiders, scorpions (Scorpiones), centipedes (Chilopoda), millipedes (Diplopoda), sow bugs (Isopoda); lizards mostly Anolis limifrons. Forages mostly 0–1 m above ground, occasionally to 5 m, and away from mixed-species flocks. Considered an obligate army-ant follower, seldom seen away from ants ; in the most extensive study, of 352 swarms attended by nesting pairs in Panama, 93·5% of these were of Eciton burchelli, remaining 6·5% being of Labidus praedator, despite estimated density of latter on study site of 4–15 swarms/km², compared with 2·5/km² of Eciton; marked birds found to visit swarms 1 km apart in course of same week, and 0·5 km apart within space of 70 minutes. Early in morning, cruising individuals, pairs, or family groups work through the forest 0·5–2 m above ground, flying up to 15 m at a time, alighting for a few seconds to peer about, then moving on; typically, first checks ants’ raiding paths and bivouac sites from previous day and, if not successful, wanders more widely, immediately investigating vocalizations of conspecifics as well as of other obligate ant-followers; once located, swarms are generally followed for most of the day; often loafs around bivouacs for extended periods, waiting for ants to raid; on days when statary swarms fail to raid, the birds often switch to another colony. Progresses by hops and short, fluttery flights; tail held slightly fanned and regularly lowered slowly to as much as 80° below plane of body, then rapidly flicked upwards to 10° or more above body level. Perches mostly below 1 m, often clinging laterally (upper leg flexed, lower leg extended) to slender vertical stems, where it pitches, yaws and pivots, or sidles up and down with great agility, also routinely using logs and horizontal perches on fallen branches; while perched, always peers intently downwards at swarming ants, spending up to a few minutes at a single perch before trying another spot; more frequently, multiple prey captures may take place within seconds if a bird is positioned near swarm front; in one study, individuals foraging at good sites over ants darted for prey every 42·6 seconds on average. Most attack manoeuvres are short sallies or sally-pounces to the ground, followed by quick hop back up to perch before ants can counter-attack; less frequently, makes short aerial sallies, or sallies to vines, lianas, logs, aerial roots, branches or foliage, or perch-gleans from these surfaces by reaching out, up or down with a quick stab of the bill or by short horizontal lunge. Dominant birds in the hierarchy mostly wait on vertical perches over the most active parts of the swarm and sally to the ground; subordinate birds much more likely to clamber about, perch-gleaning or sallying to other substrates. When fleeing prey darts under leaf litter, the antbird sallies to or pounces on the spot and, with legs splayed, begins to toss leaves with the bill until arthropod uncovered; frequently makes bounding, zigzag pursuit in hops and short flights through swarm to follow evasive manoeuvres of prey. All but largest items consumed immediately, with minimal handling time; holds large prey in the bill by an appendage, shakes it vigorously until appendage falls off, then continues systematically to remove other appendages and to dissect body segments before swallowing. Subordinate individuals often displaced to less favourable positions at periphery of swarms or to higher perches, and may follow ant probes as high as 5 m up trees; individuals low in the pecking order sometimes resort to “stealing” prey from army ants carrying food back to bivouacs. Dominates over and aggressively displaces and supplants the smaller Hylophylax naevioides and other non-obligate ant-followers at swarms, but typically subordinate to larger Phaenostictus mcleannani, as well as to larger species of woodcreeper (Dendrocincla, Dendrocolaptes, Xiphorhynchus, Hylexetastes) and ground-cuckoo (Neomorphus) in areas where these also occur. Interspecific aggression usually elicits only low-intensity displays; intraspecific aggression more common, typically elicits higher-intensity responses. Nevertheless, on Barro Colorado I, Panama, where Phaenostictus mcleannani became extinct c. 3 decades ago, it is not the present species that has benefit, but Hylophylax naevioides, whose numbers have increased dramatically in response.

Loudsong a series (e.g. ten notes, 2·1 seconds) starting with long, slightly upslurred whistles that shorten rapidly and gain in intensity, followed by shorter notes that drop in pitch and intensity before becoming harsh; quite variable in length, but basic patterns of change of note shape and length and intensity remain. For differences in song from formerly conspecific G. leucaspsis, see Taxonomy (above). No known differences in calls between present species and G. leucaspsis.

Season Mar–Jan (concentrated in Apr–Sept) in Costa Rica and Apr–Dec in Panama, although some authors have reported season to be late Feb to early Sept in last-named country. Territory maintained year-round. Monogamous. Nest descriptions from Costa Rica and Panama: a simple cup consisting of anything from a few to more than 100 strips of dead palm leaves and fragments of other dead leaves, usually pressed into bottom of or wedged across a cavity 6–10 cm in diameter and 10 cm or more deep in top of rotting stub or stump, once in sheathing base of upright fallen palm frond balanced precariously against tree, often thin lining of rhizomorphs (to which both adults often continue to add during incubation); nests have been found in stumps of the palms Scheelea zonensis, Oenocarpus panamensis and Euterpe; height above ground of 13 nests in Panama 0·1–1·5 m (median 0·4 m); same nest occasionally used twice. Normal clutch two eggs, white to creamy or light vinaceous fawn, heavily streaked and splotched longitudinally with dark reddish brown; incubation by male for much of morning, relieved in early afternoon by female, then male often takes another late-afternoon shift, before yielding to female for entire night, incubation period in Panama 15 days at one nest, 16 days at another; both parents brood and feed chicks, food items usually dissected and legs removed before brought to nest (particularly when nestlings only a few days old); at a nest in Panama, male fed young 79 times and female 62 times in 53·6 hours, average interval between feeds 38 minutes for male and 41 minutes for female; largest item delivered was a lizard (Anolis limifrons) c. 2·5 cm in length from snout to vent; when nestlings 1–2 days old parents swallowed faecal sacs and then brooded, later in period carried sacs away; brooding during day ceased when young 6–13 days old; nestling period at 3 nests was 14 days, 13–14 days and 14–15 days. In two studies in Panama, success was 28% (5 of 18 nests fledged at least one young) and 33% (1 of 3), and predation rates at watched nests compared with unwatched nests determined to be roughly the same; during many years of study, no pairs known to nest successfully more than once in a year, although pairs that failed in first attempt repeatedly attempted to renest. Mean annual survival rate at a locality in Panama estimated at 61%, with a longevity record of 11·5 years.

Not globally threatened (Least Concern). Fairly common throughout its extensive range. Occurs in numerous formally protected large areas, e.g. Braulio Carrillo and Corcovado National Parks, La Amistad International Park, and La Selva Biological Reserve, in Costa Rica, and Soberanía and Darién National Parks, in Panama; also in several privately owned reserves centred on ecotourism lodges. Range also encompasses extensive intact habitat which is not formally protected, but is still at low risk of development in immediate future. Has suffered some local habitat contractions and consequent range fragmentation as a result of widespread deforestation in parts of its range; local populations in Honduras, Nicaragua and parts of Costa Rica and Panama have declined or disappeared as entire regions have been cleared for human settlement and agriculture. In W Ecuador, the species was formerly found S to coastal El Oro, but no recent reports from S of E Guayas and NW Azuay; now very local in SW, and has disappeared from Río Palenque Science Centre.