Yellow Tyrannulet

The yellow tyrannulet is 10 to 11.5 cm (3.9 to 4.5 in) long and weighs about 8 grams (0.28 oz). The sexes have the same plumage. Adults of the nominate subspecies C. f. flaveola have a dark yellowish olive crown with a somewhat bushy crest. They have a bright yellow supercilium, a bright yellow partial eye ring, and a dark line through the eye on an otherwise yellowish face. Their upperparts are dark yellowish olive. Voice: The yellow tyrannulet is very vocal; its songs vary across its wide range and often include duets. In Costa Rica it sings a "sputtering series of wheep or wee-deep notes". In Ecuador the song is described as "a pleasant and rollicking series of notes that often seem to lack much pattern, usually starting slowly but then quickly speeding up".