Chestnut-headed Oropendola
Psarocolius wagleri
Chestnut-headed oropendola males average 35 cm (14 in) long and females 28 cm (11 in). Males weigh an average of 214 g (7.5 oz) and females 113 g (4.0 oz). The species looks very long-winged in flight. Males have a slight crest. Adult males of the nominate subspecies have a dark purplish chestnut head, throat, and upper breast. Their body and wings are mostly black with a bluish gloss. Their rump and uppertail coverts are dark chestnut and their rear flanks and undertail coverts a medium chestnut.
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: Chestnut-headed Oropendola and Russet-backed Oropendola.