Mountain Elaenia
Elaenia frantzii
The mountain elaenia is 14 to 15 cm (5.5 to 5.9 in) long and weighs about 14 to 24 g (0.49 to 0.85 oz). It is a small to medium size elaenia with a rounded crest. The sexes have the same plumage. Adults of the nominate subspecies have a brownish olive head with lighter cheeks, a thin very pale olive eyering, and a mostly hidden white patch on the crown. Their upperparts are grayish olive. Their wings are mostly dusky with pale olive or olive-yellow edges on the flight feathers. The tips of their wing coverts are yellowish olive and show as two bars on the closed wing. Voice: The northern and southern pairs of subspecies of the mountain elaenia have somewhat different vocalizations, which is part of the evidence hinting that they are separate species. The dawn song of the northern pair is "an endless repetition of an overslurred whistle followed by a rising burry part and a higher-pitched second overslurred note, all three notes interconnected without a clear pause".
ID text from Wikipedia, CC BY-SA 4.0
Yellow-crowned Tyrannulet
Tyrannulus elatus
The yellow-crowned tyrannulet is 10 to 11 cm (3.9 to 4.3 in) long and weighs 6.5 to 8 g (0.23 to 0.28 oz). Adult males have a slate-gray to dark brown or blackish crown with a bright yellow to orange-yellow stripe along its middle. Their nape and back are bright olive-green. They have a grayish supercilium, a thin dark line through the eye, and a pale gray lower face. Their wings are dusky with two white to yellowish white bars. Their tail is dusky olive. Their throat is pale gray and their underparts pale to medium yellow with an olive wash on the breast. Voice: The yellow-crowned tyrannulet's song is a "2-noted, clear, plaintive 'wih-weér' (or 'free beer'), 2nd note higher, shorter, and stressed". It apparently differs little across the species' range.
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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