HBW 11 - Species accounts: Tropical Gnatcatcher (Polioptila plumbea)

10. Tropical Gnatcatcher

Polioptila plumbea

French: Gobemoucheron tropical German: Amazonasmückenfänger Spanish: Perlita Tropical

Other common names: Maranon/Mountain Gnatcatcher (maior); White-browed Gnatcatcher (“bilineata group”)

Taxonomy. Todus plumbea J. F. Gmelin, 1788, Suriname.

Possibly forms a superspecies with P. lactea, and some earlier suggestions that the two may be conspecific. Because interspecific morphological variation within this genus is often very subtle, it is thought likely that this taxon consists in fact of several species; study of genetic and vocal characters of various populations clearly warranted. Races form at least three distinct groups, i.e. the “bilineata group” (also including superciliaris, brodkorbi and cinericia), the “nominate group” (with anteocularis, daguae, innotata, parvirostris, plumbiceps and atricapilla) and maior; last-mentioned is almost certainly a separate species. Relative distributions of nominate race and innotata in E Brazil (in region roughly from C Pará E to WC Maranhão) unclear; more study needed. Records from E Ecuador and adjacent N Peru (NW Loreto) tentatively considered to refer to race parvirostris; locality of a specimen labelled as this race from W Brazil (C Amazonas) is roughly equidistant from localities of specimens representing innotata, nominate and parvirostris. Original description of cinericia based on comparison with bilineata, rather than with adjacent mainland superciliaris; further study needed to clarify whether cinericia should be synonymized with latter. Twelve subspecies recognized.

Subspecies and Distribution.

P. p. brodkorbi Parkes, 1979 – lowlands of S Mexico (E Veracruz and NE Oaxaca E to E Yucatán Peninsula) S through lowlands of N & EC Guatemala and Belize to N Costa Rica.

P. p. superciliaris Lawrence, 1861 – lowlands from NC Costa Rica S to S Panama, possibly to N Colombia.

P. p. cinericia Wetmore, 1957 – Coiba I, off S Panama.

P. p. bilineata (Bonaparte, 1850) – Caribbean and Pacific coasts of NW Colombia S, W of Andes, to NW Peru (NW La Libertad).

P. p. daguae Chapman, 1915 – upper Cauca Valley (C Valle S to CS Cauca), in S Colombia.

P. p. anteocularis Hellmayr, 1900 – upper Magdalena Valley (Huila), in S Colombia.

P. p. plumbiceps Lawrence, 1865 – NE & E Colombia (C La Guajira S in lowlands to CN Boyaca, SC Casanare and C Meta) and Venezuela (including Margarita I).

P. p. innotata Hellmayr, 1901 – E Colombia (E Vichada, NE Guainia) E to C Guyana and N Brazil (S to NE Roraima, W Pará, N Tocantins and C Goiás).

P. p. plumbea (J. F. Gmelin, 1788) – Suriname, French Guiana, and N Brazil (C to NW Pará, E & NW Maranhão).

P. p. parvirostris Sharpe, 1885 – E of Andes in E Ecuador, N Peru (Loreto S to N San Martín) and NW Brazil.

P. p. maior Hellmayr, 1900 – upper Marañón Valley (C Amazonas S through C & E Cajamarca, E Piura and E La Libertad), in NW Peru.

P. p. atricapilla (Swainson, 1832) – NE Brazil (lowlands from C Maranhão E to Ceará and Pernambuco and S to E & C Bahia).

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Descriptive notes. 10–12 cm; 6–8 g. Bill short and slender, narrowing to fine, slightly hooked tip. Male nominate race has sharply defined glossy black crown extending to eye, nape and side of neck, sharply contrasting with bluish-grey hindneck, back and rump; remiges blackish, edged with grey, tertials edged white (but less pronounced than in P. albiloris); tail black, outer rectrices mostly white with slight black base, amount of white decreases on each succeeding pair of outer rectrices, innermost pair completely black; underparts whitish, tinged with grey on breast and side; iris dark sepia-brown; upper mandible blackish, lower mandible blue-grey with blackish tip; legs black. Female is similar to male, but crown, side of head and nape grey, similar to back in coloration. Juvenile resembles female. Racial differences revolve mostly around facial markings, presence or absence of black on head of female, darkness of overall plumage, and measurements of wing, bill and tail: anteocularis is darker overall than nominate, with slate-grey mantle, wing slightly shorter than tail; daguae has darker, slate-grey back, black cap not extending to lores, which are white, outer rectrices mostly white; plumbiceps is similar to last but dull grey (not so dark) above, wing slightly longer than tail; innotata has less extensive white edgings on tertials; parvirostris has more extensive black on auriculars and lores; atricapilla has whitish cheek, throat and underparts, female with black streak on ear-coverts; male bilineata has broad white supercilium, white lores, thin black postocular stripe (giving white-faced appearance), female similar but black areas of head replaced by dark grey, black spot at edge of crown behind ear-coverts, both sexes with white underparts; brodkorbi differs from previous in having purer grey (less brownish) upperparts, greyer edgings of remiges, and more extensive white at tips of rectrices 4 and 5, female lacks black spot behind ear-coverts; superciliaris and cinericia are darker than last two, with edges of remiges grey, underparts washed blue-grey; maior is darker bluish-grey on upperparts than other races, male has black cap, lacks white supercilium, female very different from others in possessing a steely-black cap with distinct white supercilium (similar to male bilineata), also a white eyering that is broken posteriorly. Voice. Vocalizations differ geographically; study needed, however, to clarify whether different renderings represent true geographical variation, individual or contextual differences, or merely contrasts in how various authors perceive sounds. Loudsong of race brodkorbi a high, silvery trill, often rippling and descending, 2–3 seconds in duration, “sweet, weet, weet, weet, weet”; also a quiet, scratchy warble, presumably analogous to complex songs given by other gnatcatcher species. Loudsong of bilineata described as a simple, rhythmic descending series of clear, high-pitched notes, “peet, peet, peet peeti peetí, ti’ti’pee, pee pee”, or “seet, weet, weet-weet, weet-pitee, weet-pitee”, usually falling slightly in pitch. Loudsong of E birds (nominate or parvirostris?) a more evenly pitched, faster and stronger “chichichichichichichi” or “chup-chup-chup”. Frequently calls while foraging, and when approaching or leaving nest, with a nasal mewing “nyaah”, “nyeeah”, “ meeah” or “chaaa”, often delivered as rapidly spaced pairs, “meeah-meah”, shorter and buzzier than mew of P. caerulea; in Panama (brodkorbi), call described as “tzeet-tzeet”; plumbiceps gives faint, insect-like chirp. Calls of atricapilla described as frequent, strident “psééeh” or “tsewk” notes, and descending “eet, eet, eet, eet”; song fast, high and somewhat varied, beginning with series of monotonous “glis” notes.

Habitat. Found in diverse habitats, including forest edge, overgrown pasture, coffee plantations, mature rainforest, flooded forest, second-growth forest, arid scrub, savanna, and mangroves. Primary ecoregions occupied by each race include: Isthmian–Atlantic and Isthmian–P acific moist forests (superciliaris); Isthmian–Pacific moist forests, Isla Coiba (cinericia); Magdalena–Urabá and Western Ecuador moist forests, Tumbes–Piura dry forests and Sechura desert (bilineata); Llanos, La Costa xeric shrublands, Maracaibo dry forests and Guajira–Barranquilla xeric scrub (plumbiceps); Magdalena Valley dry forests (anteocularis); Patia Valley dry forests (daguae); Guyanan savanna and Guianan moist forests (innotata); Guianan, Tapajós–Xingu, Uatuma–T rombetas and Tocantins/Pindare moist forests (nominate); Marañón dry forests and Peruvian Yungas (maior); Ucayali moist forests (parvirostris), Caatinga, Maranhão Babaçu forests, and Cerrado (atricapilla); and Central American dry forests and Isthmian–Atlantic, Central American Atlantic, Petén–Veracruz and Yucatán moist forests (brodkorbi). Mostly below 1000 m; maior mostly at 2000–2 500 m, higher than other polioptilids.

Food and Feeding. Feeds on small arthropods and spiders (Araneae). In Venezuela, 55% of prey items obtained from stomach emetic samples were small (less than 5 mm long) beetles (Coleoptera), 24% were ants (Hymenoptera), 10% were insect eggs, pupae or larvae, and 7% were wasps (Hymenoptera); items larger than 5 mm in size comprised 13% of sample in frequency of capture. Actively gleans and hover-gleans from terminal twigs or leaves at various levels, ranging from forest canopy to near ground; avoids dark undergrowth. Regularly follows mixed foraging flocks of other insectivorous birds.

Breeding. Breeding reported mid-Mar in Mexico (Veracruz), Feb–Jun in Costa Rica, Mar–Oct in N Colombia, Feb–Apr in SW Ecuador (after rainy season), mid-Jun in Venezuela and mid-Jul to late Oct in Suriname; second broods probable, but undocumented. Often observed in pairs throughout year, suggesting maintenance of permanent pair-bond. Apparent courtship display described for race anteocularis; male responds to whining calls of female with a soft, steady song given while in erect posture with bill pointed upwards, male turns so as to orient black crown patch towards female. Both sexes involved in construction of nest, a deep cup, walls composed of moss and tree bark bound by cobwebs, lined with vegetation and leaf fibres, lichens affixed to outer wall, externally c. 5–6 cm across and c. 6–7 cm in height, inner cup c. 3–4 cm in diameter and 3–4 cm deep; placed at heights above ground varying from 1 m to 38 m, supported by twigs or branches, often conspicuous. Clutch 2–4 eggs, pale bluish with brown speckles, laid one per day, usually in morning; incubation by both sexes, female sitting at night, eggs occasionally left uncovered for short periods (c. 2–21 minutes) during morning hours, incubation period 13 days; both sexes also brood and feed chicks, which leave nest at 12–14 days; both sexes occasionally perform apparent distraction display when disturbed, flying slowly away while rapidly vibrating wings to entice predators away from nest. In Ecuador, 63% of nests of race bilineata successfully hatched eggs, and 61% of nestlings fledged.

Movements. Resident.

Status and Conservation. Not globally threatened. Common and widespread in Panama, Venezuela, Colombia and Suriname. In Ecuador, fairly common to common W of Andes but uncommon and local E of Andes. Fairly common in Caribbean lowlands of Guatemala, uncommon in Petén; common and widespread in Belize. Common in Pacific and Atlantic lowlands of Costa Rica, but scarce or absent in N Guanacaste and most of Nicoya Peninsula. Three races are of potential conservation concern owing to limited distributions in ecoregions considered to be “Critically Endangered” or “ Endangered”; these are maior, anteocularis and daguae. No information about status of Coiba I race (cinericia).

Bibliography. Binford (1989), Carriker (1910), Chapman (1917), Cherrie (1916), Clark (1902), Cracraft (1985), Haverschmidt & Mees (1994), Hilty (2003), Hilty & Brown (1986), Howell & Webb (1995), Jones et al. (2002), Lamm (1948), Land (1963), Lee Jones (2004), Marchant (1960), Meyer de Schauensee (1966), Meyer de Schauensee & Phelps (1978), Miller (1952), Monroe (1968), Olson et al. (2001), Parkes (1979), Pople et al. (1997), Poulin et al. (1994), Ridgely & Greenfield (2001), Ridgely & Tudor (1994), Russell (1964), Salaman (1994), Sick (1993), Skutch (1960, 1985), Slud (1964), Snyder (1966), Stiles & Skutch (1989), Stotz et al. (1996), Williams & Tobias (1994), Zimmer (1942).