Species of bird
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The Loja tyrannulet (Zimmerius flavidifrons) is a species of bird in the family Tyrannidae, the tyrant flycatchers. It is found in Ecuador and Peru.
Taxonomy and systematics.
The Loja tyrannulet was originally described as "Tyrannulus flavidifrons". It was later reclassified as a subspecies of the golden-faced tyrannulet (then "Tyrannulus chrysops", now "Zimmerius chrysops"). Through much of the twentieth century the golden-faced tyrannulet and several other tyrannulets were kept in genus "Tyranniscus" but a study published in 1977 erected the present genus "Zimmerius" for them.
Beyond its transfer to "Zimmerius" as a subspecies of the golden-faced tyrannulet, the Loja tyrannulet's taxonomy is unsettled. The International Ornithological Committee (IOC) follows a study published in 2008 and splits it from the golden-faced tyrannulet as a monotypic species. However, the South American Classification Committee of the American Ornithological Society, the Clements taxonomy, and BirdLife International's "Handbook of the Birds of the World" (HBW) treat it as a subspecies of the Peruvian tyrannulet ("Z. viridiflavus"). 
This article follows the monotypic species IOC model.
Description.
The Loja tyrannulet is about long and weighs . The sexes have the same plumage. Adults have pale yellowish lores and eye-ring and a dark stripe through the eye on an otherwise grayish olive face. Their crown is darkish olive to grayish olive and their back and rump are bright olive. Their wings are dark dusky with bright yellow-green edges on the coverts and flight feathers. Their tail is dusky olive. Their throat is pale yellow, their breast and flanks pale olive-yellow with some olive markings, and their belly very pale yellow to white. They have a gray to medium brown iris with a tan rim, a small, rounded, bill whose maxilla is gray to blackish and mandible medium gray, and dark gray to black legs and feet.
Distribution and habitat.
The Loja tyrannulet is found in Ecuador west of the Andes from southeastern Chimborazo Province south to western Loja Province and in the extreme southeast in the Zumba region of Zamora-Chinchipe Province. Its range extends into the northern Peruvian departments of Tumbes and Piura. It inhabits the canopy, edges, and clearings of humid forest and woodlands in the subtropical zone. In elevation it ranges between in Ecuador, between in Tumbes, and between in Piura.
Behavior.
Movement.
The Loja tyrannulet is a year-round resident throughout its range.
Feeding.
The Loja tyrannulet feeds on insects; it probably also feeds on small fruits like those of mistletoes (Loranthaceae). It forages singly or in pairs and often joins mixed-species feeding flocks. It feeds mostly in the forest canopy, perching horizontally with its tail cocked and actively moving about and gleaning food while perched or with short flights.
Breeding.
Nothing is known about the Loja tyrannulet's breeding biology.
Vocalization.
The Loja tyrannulet's dawn song is "a fast 'ti tuueé' " and its call "a loud and sharp, drawn-out 'truuu-eeé' ".
Status.
The IUCN follows HBW taxonomy and so has not separately assessed the Loja tyrannulet from the Peruvian tyrannulet. The Loja tyrannulet is considered common in Ecuador. 
References.
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