Ashy-headed Greenlet
Hylophilus pectoralis
The ashy-headed greenlet is 12 cm (4.7 in) long and weighs 10.3 to 12.4 g (0.36 to 0.44 oz). The sexes have the same plumage. Adults have a dull gray forehead, crown, and nape. They have a dull grayish white supercilium and grayish ear coverts. Their upperparts are dull greenish. Their wings and tail are dull greenish with brighter greenish edges on the feathers. Their chin is off-white, their throat mottled grayish white, their breast greenish yellow, their flanks grayish, and their belly dull white. Voice: The ashy-headed greenlet's song is a "high, hurried Wéeje-Wéeje-Wéeje-, rapid tutjeweé-tutjeweé-tutjeweé-, loud, sharp WúTjirrrr".
ID text from Wikipedia, CC BY-SA 4.0
Lemon-chested Greenlet
Hylophilus thoracicus
The lemon-chested greenlet is 10 to 13 cm (3.9 to 5.1 in) long and weighs 11 to 14 g (0.39 to 0.49 oz). The sexes have the same plumage. Adults of the nominate subspecies H. t. thoracicus have an ochraceous olive forehead, a dull grayish olive crown, and a wide grayish nape collar. They have grayish lores and sides of the head with a greenish tinge on the ear coverts. Their upperparts are bright olive that often has a yellowish tinge. Their wings' coverts and flight feathers are dull blackish gray with wide bright olive to yellowish green edges on the latter. Voice: The lemon-chested greenlet's song is a "very high, rapid series of 10-15 upslurred tu-Weéet notes". Its call is a "rich, whistled where-it sometimes doubled ".
ID text from Wikipedia, CC BY-SA 4.0

Where you might meet both
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Play today's Daily BirdPhotos and recordings are credited to their authors under the licence shown. Full profiles: Ashy-headed Greenlet and Lemon-chested Greenlet.