Plain xenops

The plain xenops (Xenops genibarbis) is a passerine bird in the Furnariinae subfamily of the ovenbird family Furnariidae. It is found in the tropical New World from southern Mexico south as far as northern Bolivia and east across Brazil.

Taxonomy and systematics
The International Ornithological Committee (IOC) and BirdLife International's Handbook of the Birds of the World (HBW) recognize these 10 subspecies of the plain xenops:


 * X. g. mexicanus Sclater, PL, 1857
 * X. g. ridgwayi Hartert, EJO & Goodson, 1917
 * X. g. littoralis Sclater, PL, 1862
 * X. g. neglectus Todd, 1913
 * X. g. remoratus Zimmer, JT, 1935
 * X. g. ruficaudus (Vieillot, 1816)
 * X. g. olivaceus Aveledo & Pons, 1952
 * X. g. obsoletus Zimmer, JT, 1924
 * X. g. genibarbis Illiger, 1811
 * X. g. alagoanus Pinto, 1954

What the IOC and HBW now treat as the white-throated xenops (X. minutus Sparrman, 1788) was also previously included as a subspecies. HBW recognized the split by 2018 and the IOC followed suit in July 2023. However, the South American Classification Committee of the American Ornithological Society (SACC) and the Clements taxonomy retain that taxon as a subspecies of the plain xenops. Because the white-throated was formally described earlier than any of the other subspecies, by the principle of priority these systems apply the binomial X. minutus to the 11-subspecies plain xenops. The SACC does state that Xenops minutus sensu lato might consist of more than one species.

Description
The plain xenops is about 11 to 13 cm long and weighs about 10 to 13 g. 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.

The other subspecies of the plain xenops differ from the nominate and each other thus:


 * 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. littoralis, dusky crown with minimal streaks, yellowish throat, more olivaceous underparts, rufous wings and tail
 * X. g. neglectus, like littoralis but slightly paler cinnamon wings and tail
 * X. g. olivaceus, very like neglectus but with more olive (less grayish) underparts
 * X. g. ridgwayi, less rufous overall, more brownish underparts than olivaceous
 * X. g. mexicanus, more rufous than ridgwayi, chestnut-rufous rump and uppertail coverts, whitish throat, somewhat rufescent underparts
 * X. g. alagoanus, very similar to nominate

Distribution and habitat
The subspecies of the plain xenops are distributed thus:


 * X. g. mexicanus, from Veracruz and Oaxaca in southern Mexico south through Belize and Guatemala into Honduras
 * X. g. ridgwayi, from Nicaragua south through Costa Rica into central Panama
 * X. g. littoralis, from Panama's Darién Province south into northern Colombia and through western Colombia and western Ecuador slightly into northwestern Peru
 * X. g. neglectus, northeastern Colombia and northwestern Venezuela
 * 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. olivaceus, Serranía del Perijá on the Colombia-Venezuela border
 * 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 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 1000 m in Mexico, to 1300 m in northern Central America, to 1500 m in Costa Rica, and to 2000 m in Colombia. It reaches 2200 m in Venezuela but is mostly found below 1500 m. In Ecuador it is mostly below 900 m but reaches 1300 m. It occurs up to 1500 m in Brazil, to 1400 m in Peru, and 1300 m in Bolivia.

Movement
The plain xenops is a year-round resident throughout its range.

Feeding
The 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.

Breeding
Most of what is known about the 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 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.

Vocalization
The song of the 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). Others renditions are "a fairly long, squeaky trill, fastest in the middle" (northern Central America), "a fast, high-pitched trill" (Costa Rica) , "a mostly ascending series of notes, e.g., 'ts-tsi-tsi-tsi-tsi-tsi' " (Ecuador) , and an "extr. high, hurried series of 5-10 x 'seep---' " (Brazil). 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", "a short Peek!" , and "a sharp 'peeyk' ".

Status
The IUCN has assessed the 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. "Though Plain Xenops appears to be somewhat tolerant of human disturbances, disappearance from disturbed forests has also been recorded."