White-throated Treerunner

Belonging to a monotypic genus within the hyper-diverse Furnariidae family, this specialized avian species is recognized by its compact, robust body and structural adaptations convergent with woodpeckers and treecreepers. It measures approximately 15 to 16 centimeters in length and weighs between 20 and 27 grams. Its most striking diagnostic feature is the brilliant white throat and upper breast, which sharply contrasts with the dark earthy-brown lower underparts, heavily patterned with conspicuous white scaling or teardrop-shaped spots. The upperparts are predominantly dark grayish-brown, transitioning to a rich rufo-castaneous rump and tail. The bill is relatively long, stout, and slightly upturned, with a dark horn-colored maxilla. Crucially, the tail feathers feature stiff, protruding shafts with bare, spiny tips that serve as a rigid prop when climbing vertical surfaces.

Geographical distribution: Endemic to the southwestern portion of South America, its range is closely tied to the temperate biomes. It occurs in Chile, spanning from the southern parts of the Valparaíso and Santiago regions down to Tierra del Fuego, and in Argentina, where it inhabits the Andean-Patagonian strip from Neuquén and western Río Negro south to the archipelago of Tierra del Fuego.

Habitat: The species is obligately associated with temperate rain forests and subantarctic forests, especially those dominated by southern beeches of the genus Nothofagus, such as Nothofagus pumilio (lenga), Nothofagus dombeyi (coihue), and Nothofagus antarctica (ñire). It exhibits a strong preference for primary, old-growth forests containing a high density of standing dead trees (snags) and mature timber rich in epiphytes, mosses, and lichens, ranging from sea level up to 1,200 meters in elevation.

Feeding: Strictly insectivorous, its diet consists primarily of coleopteran larvae, spiders, ants, centipedes, and various other sub-cortical arthropods. It searches for food by hitching up tree trunks, using its specialized bill to probe deep into crevices, rotting wood, and underneath bark flaps, often flaking off pieces of bark to expose hidden prey.

Behavior: Typically observed singly or in pairs, and frequently associates with mixed-species foraging flocks, often led by the thorn-tailed rayadito (Aphrastura spinicauda). It moves dynamically along tree trunks in a jerky, upward spiral trajectory, using its spiny tail as a support. The flight is short, rapid, and undulating. Its vocal repertoire includes a distinctive, sharp, metallic "tsip" or "clik" call, repeated at irregular intervals.

Nesting: It is a primary cavity nester, excavating its own nesting chamber in the soft, decaying wood of dead standing trees or dead branches of living trees, typically at heights of 3 to 15 meters above the ground. The chamber entrance is circular, leading to a deep cavity lined with soft plant fibers. The female lays a clutch of 2 to 3 pristine white, oval-shaped eggs between October and January. Both parents actively participate in excavating the cavity, incubating the eggs, and provisioning the altricial chicks.

Conservation status: Currently listed as Least Concern (LC) on the IUCN Red List. Nevertheless, the species is highly sensitive to habitat fragmentation, industrial logging, and the removal of dead wood, as the loss of mature forest elements directly reduces both foraging substrates and nesting sites.