Mottle-cheeked Tyrannulet

This is a small passerine bird belonging to the tyrant flycatcher family, recognized by its delicate size and plumage dominated by olive-green upperparts and pale yellow underparts, which transition to a subtle grayish-green wash on the chest and flanks. Adults measure between 11.5 and 12 centimeters in length and weigh around 8 to 9.5 grams. Its most diagnostic facial features are the conspicuous whitish supercilium, a dark transocular stripe, and distinctively mottled dusky and white cheeks that give the species its common name. The wings feature two narrow, pale yellowish wing bars, and the bill is relatively short, fine, and blackish.

Geographical distribution: It displays a disjunct distribution across South America, with two major population groups. The nominate subspecies occupies southeastern and southern Brazil, eastern Paraguay, Uruguay, and northeastern Argentina. A separate population is restricted to the montane Yungas forests, stretching from western Bolivia southward into northwestern Argentina, including the provinces of Jujuy, Salta, and Tucumán.

Habitat: This species primarily occupies the mid-story and canopy of humid subtropical and temperate forests, notably the Atlantic Forest block, gallery forests, humid montane Yungas, and mature secondary woodlands. It is also found along forest edges, clearing borders, and humid shrublands, ranging from sea level up to 2500 meters above sea level in the Andean slopes.

Feeding: Its diet is strictly insectivorous, consisting of small arthropods, including midges, small beetles, leafhoppers, caterpillars, and spiders. It is a highly active forager, scanning the outer foliage of trees and employing hover-gleaning and rapid upward sallying techniques to pluck prey from the undersides of leaves and twigs.

Behavior: This avian species is remarkably energetic, moving constantly with a characteristic habit of twitching one wing at a time in an upward, jerky motion. It is a frequent and core member of mixed-species feeding flocks, moving through the forest alongside warblers, tanagers, and other small tyrant flycatchers. Its vocalizations are high-pitched, featuring a rapid, descending trill that is useful for locating individuals within dense foliage.

Nesting: The breeding season takes place during the austral spring and summer, generally from October to January. It constructs a globular or bag-shaped nest with a side entrance near the top. The structure is built using green mosses, lichens, plant fibers, and spider webs, which help anchor the nest to hanging branches, vines, or epiphytic growth. The interior is lined with softer vegetable down. The female typically lays 2 to 3 white, unmarked eggs, which she incubates for about 14 to 16 days while both parents cooperate in feeding the nestlings.

Conservation status: It is currently classified as Least Concern (LC) on the IUCN Red List of Threatened Species. Although it faces localized pressures from habitat fragmentation and deforestation within the Atlantic Forest biome, its extensive range, adaptability to secondary habitats, and stable population trends prevent it from meeting the thresholds for threatened status.