Amazonian plain xenops

The Amazonian plain xenops was formerly described in 1811 by the German zoologist Johann Illiger based on a specimen collect near Cametá in northeast Brazil. He coined the binomial name Xenops genibarbis where the specific epithet combines Latin gena meaning "cheek" with barba meaning "beard".^[2][3][4] The Amazonian plain xenops was formerly considered specific with the northern plain xenops. The two species were split based on differences in plumage, vocalizations and DNA sequence.^[5][6]

Five subspecies are recognised:^[5]

• X. g. remoratus Zimmer, JT, 1935 – east Colombia, south Venezuela and northwest Brazil
• X. g. ruficaudus (Vieillot, 1816) – east Colombia, Venezuela, the Guianas and north Brazil
• X. g. obsoletus Zimmer, JT, 1924 – east Ecuador, east Peru, north Bolivia and west Brazil
• X. g. genibarbis Illiger, 1811 – central north Brazil (south of the Amazon)
• X. g. alagoanus Pinto, 1954 – northeast Brazil

The Amazonian plain xenops is about 11 to 13 cm (4.3 to 5.1 in) long and weighs about 10 to 13 g (0.35 to 0.46 oz). Its bill is wedge-shaped, fairly stubby, and slightly upturned. The sexes are alike and juveniles resemble adults. Adults of the nominate subspecies X. g. genibarbis have a conspicuous buff or whitish supercilium and a wide pure white malar stripe. Their upperparts are dull brown to rufous brown and unstreaked; their crown is darker and lightly streaked. Their tail is cinnamon with much black. Their wings are also cinnamon, with a wide ochraceous band on the flight feathers. Their throat is pale with olivaceous edges to the feathers. The rest of their underparts are plain dull grayish brown with some light buff spotting on the foreneck and breast. Their iris is dark brown, their maxilla dull black, their mandible dull grayish white with a dark gray tip, and their legs and feet bluish gray. The minimal streaking and the wide malar stripe set this species apart from other xenops.^[7]

The other subspecies of the Amazonian plain xenops differ from the nominate and each other thus:^{[7][8][9][10][11][12][excessive citations]}

• X. g. ruficaudus, darker crown, more olivaceous underparts, foreneck and breast more spotted
• X. g. obsoletus, less rufous in the crown, paler cinnamon tail, foreneck and breast less spotted
• X. g. remoratus, little or no crown streaking, duller above and below, ill-defined breast markings
• X. g. olivaceus, very like neglectus but with more olive (less grayish) underparts
• X. g. alagoanus, very similar to nominate

The subspecies of the Amazonian plain xenops are distributed thus:^[5][7]

• X. g. remoratus, eastern Colombia, southwestern Venezuela, and northwestern Brazil north of the Amazon and east to the Rio Negro
• X. g. ruficaudus, eastern Colombia, southern and eastern Venezuela, the Guianas, and northern Brazil north of the Amazon and east of the Rio Negro
• X. g. obsoletus, eastern Ecuador, eastern Peru, northern Bolivia, and western Brazil south of the Amazon and east to the Rio Madeira
• X. g. genibarbis, central Brazil south of the Amazon from the Rio Madeira east to Piauí state and south to Mato Grosso and Goiás states
• X. g. alagoanus, northeastern Brazil between Paraíba and Alagoas states

The Amazonian plain xenops inhabits the interior and edges of a variety of forested landscapes including terra firme and várzea forests in the tropical lowlands, semideciduous forest, and mature secondary forest. In elevation it occurs up to 1,000 m (3,300 ft) in Mexico, to 1,300 m (4,300 ft) in northern Central America, to 1,500 m (4,900 ft) in Costa Rica, and to 2,000 m (6,600 ft) in Colombia. It reaches 2,200 m (7,200 ft) in Venezuela but is mostly found below 1,500 m (4,900 ft). In Ecuador it is mostly below 900 m (3,000 ft) but reaches 1,300 m (4,300 ft). It occurs up to 1,500 m (4,900 ft) in Brazil, to 1,400 m (4,600 ft) in Peru, and 1,300 m (4,300 ft) in Bolivia.^{[7][8][9][10][11][12][excessive citations]}

The Amazonian plain xenops is a year-round resident throughout its range.^[7]

The Amazonian plain xenops' diet is almost entirely arthropods, both adult and larval. It has been recorded eating termites, Hymenoptera like ants and bees, beetles, katydids, millipedes, and spiders. It typically forages from the forest understory to its mid level but does ascend to the canopy. It often joins mixed-species foraging flocks. It captures prey by gleaning, hammering, chiseling, and prying with its upturned bill. It does much of its foraging on fairly thin dead branches, often rotten ones and those that have fallen into the understory, and also feeds along vines.^{[7][8][9][10][11][excessive citations]}

Most of what is known about the Amazonian plain xenops' breeding biology is from Skutch's Life Histories of Central American Birds. In Costa Rica and Panama it breeds between December and June. Both members of a pair excavate a cavity in rotten wood, usually 3 to 10 m (10 to 30 ft) above ground, and line it with soft plant material. They also use cavities excavated by small woodpeckers. The clutch size is two eggs and sometimes two broods are raised in a year. The incubation period is 15 to 17 days and fledging occurs 13 to 14 days after hatch. Both parents incubate the clutch and provision the nestlings.^[13]

The song of the Amazonian plain xenops has some geographical variation. It has been variously described as "a very fast chattering trill, accelerating then slowing at end, dit dit dit-dit 'dt'd'd'd'd'd'd'd'd'a'a'a" (Colombia) and "a slightly descending, slightly accelerating, series of high, lisping, rising notes, usually a pause before the last note: wisst wisst-wisst-wisst-wisst wisst" (Peru).^[7] Others renditions are "a fairly long, squeaky trill, fastest in the middle" (northern Central America),^[8] "a fast, high-pitched trill" (Costa Rica),^[9] "a mostly ascending series of notes, e.g., 'ts-tsi-tsi-tsi-tsi-tsi' " (Ecuador),^[11] and an "extr. high, hurried series of 5-10 x 'seep---' " (Brazil).^[12] Descriptions of its calls also vary: "a soft chip, uttered singly or rapidly in a trill", "a thin tseep and a lisping hiss, psssi", "high spi! notes, singly or in series",^[7] "a short Peek!",^[8] and "a sharp 'peeyk' ".^[11]

The IUCN has assessed the Amazonian plain xenops as being of Least Concern. It has a very large range, but its population size is not known and is believed to be decreasing. No immediate threats have been identified.^[1] "Though Plain Xenops appears to be somewhat tolerant of human disturbances, disappearance from disturbed forests has also been recorded."^[7]