Crested Oropendola
Psarocolius decumanus
Male crested oropendolas of the nominate subspecies P. d. decumanus average 47 cm (19 in) long and females 37 cm (15 in). Males weigh about 285 g (10 oz) and females about 160 g (5.6 oz). Adult males have long feathers on their nape that form a crest. They are mostly a slightly glossy black with a chesnut rump, uppertail coverts, and undertail coverts. Their central pair of tail feathers are black and the rest yellow. Adult females are overall duller than males; they are brownish tinged rather than pure black and have a minimal crest. Voice: The male crested oropendola's display song "usually starts with low-pitched liquid notes, accelerates into variable and complex rattling crescendo, and ends with 2–3 seconds of rhythmic wing-flaps". One description calls it "very complex, including very high, rapid, staccato flutes and liquid curls".
ID text from Wikipedia, CC BY-SA 4.0
Russet-backed Oropendola
Psarocolius angustifrons
Russet-backed oropendola males are 44 to 48 cm (17 to 19 in) long and females 34 to 38 cm (13 to 15 in). Males weigh about 250 to 470 g (8.8 to 17 oz) and females about 170 to 230 g (6.0 to 8.1 oz). Adult males have long feathers on their nape that form a crest and females do not; their plumage is otherwise the same. Adult males of the nominate subspecies P. a. angustifrons have an olivaceous-brown head and a mostly brown body and wings with a russet tinge. Their rump and uppertail coverts are paler russet-brown.
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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Play BeakBrainPhotos and recordings are credited to their authors under the licence shown. Full profiles: Crested Oropendola and Russet-backed Oropendola.