The yellow tyrannulet (Capsiempis flaveola) is a small passerine bird in subfamily Elaeniinae of family Tyrannidae, the tyrant flycatchers. It is found in Costa Rica, Nicaragua, Panama, and in every mainland South American country except Chile and Uruguay.
Taxonomy and systematics
The yellow tyrannulet was originally described in 1823 as Muscicapa flaveola and in 1859 moved to the newly created genus Capsiempis. In the 1970s that genus was merged into Phylloscartes but by 1990 it had been resurrected. The yellow tyrannulet is the only member of genus Capsiempis.
The yellow tyrannulet has these five subspecies:
C. f. semiflava (Lawrence, 1865)
C. f. cerula Wetmore, 1939
C. f. leucophrys Berlepsch, 1907
C. f. magnirostris Hartert, EJO, 1898
C. f. flaveola (Lichtenstein, MHC, 1823)
Description
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. Their wings and tail are dusky olive with pale yellow to buffy yellow edges on the flight feathers and tips on the wing coverts; the last show as two wide but indistinct wing bars. Their throat and underparts are bright yellow with an ochraceous tinge on most of the breast and an olive tinge on its sides.
Subspecies C. f. semiflava has much paler yellow underparts and somewhat more distinct wing bars than the nominate. C. f. leucophrys is the largest subspecies and has the longest bill. It has a mostly white supercilium and a whitish throat. C. f. cerula is next in size after leucophrys and resembles it but with an entirely yellow supercilium like the nominate. C. f. magnirostris has the thickest bill of the subspecies. It is otherwise like the nominate except for...
