Fan-tailed warbler

{{short description|Species of bird}}

{{about|the New World warbler|the Old World warbler|zitting cisticola}}

{{speciesbox

| image = Fan-tailed Warbler - Chiapas - Mexico S4E7230 (22445769633).jpg

| status = LC

| status_system = IUCN3.1

| status_ref = {{cite iucn |author=BirdLife International |date=2020 |title=Basileuterus lachrymosus |volume=2020 |page=e.T22721955A137221917 |doi=10.2305/IUCN.UK.2020-3.RLTS.T22721955A137221917.en |access-date=11 November 2021}}

| genus = Basileuterus

| species = lachrymosus

| authority = Bonaparte, 1850

| synonyms = Euthlypis lachrymosa

| range_map = Euthlypis lachrymosa map.svg

| range_map_caption =

}}

The fan-tailed warbler (Basileuterus lachrymosus) is a New World warbler in the genus Basileuterus that lives along the Pacific slope from northern Mexico to Nicaragua. Vagrant records exist for Arizona, New Mexico and Texas. It is yellow on its throat and underparts with a tawny wash on its chest. The head is gray with a black-framed yellow crown and white around the eyes. The undertail coverlets are white. They are 5.8-6.3 in (14.5–16 cm) long and have pleasant, upslurred song. Fan-tailed warblers live in and at the edge of evergreen and semideciduous forest, especially near ravines. They eat ants, especially army ants, and are seen hopping around on either the forest floor or close to it. They are found alone or in pairs.

Fan-tailed warblers are known to engage in commensal feeding, wherein prey that has been roused or disturbed by the foraging or hunting of another animal is opportunistically captured. They have been observed following and foraging for prey near army ants, other passerines, and nine-banded armadillos.{{cite journal|last=Schaefer|first=Richard R.|author2=Jesse F. Fagan|title=Commensal foraging by a fan-tailed warbler (Euthlypis lachrymosa) with a nine-banded armadillo (Dasypus nocemcinctus) in southwestern Mexico|journal=The Southwestern Naturalist|date=December 2006|volume=51 | issue = 4|pages=560–61|url=http://www.srs.fs.usda.gov/pubs/ja/ja_schaefer009.pdf|doi=10.1894/0038-4909(2006)51[560:cfbafw]2.0.co;2}}

The fan-tailed warbler is sometimes placed in the monotypic genus Euthlypis due to its unique morphology, but its nest, eggs, voice, and juvenile plumage are consistent with Basileuterus.