There are two species of Oropendolas common in Cost Rica and at Maquenque, the Montezuma Oropendola (3 photos here) and the less common Chestnut-headed Oropendola (1 photo here). There are two more Oropendolas in Central America, both in Panama with the Crested Oropendola occasionally coming over the border into southern Costa Rica and the Black Oropendola is found only further in southern Panama. Male & female appear the same in all Oropendolas.
This week at Maquenque I observed a mother Montezuma Oropendola feeding a baby or juvenile blackbird (either a Melodious Blackbird or a Giant Cowbird if the eye is red like some said). It was interesting to watch and the pair are in one photo below and I featured them in a post while I was there titled A BLM Example in Nature.
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Mother Montezuma Oropendola & baby Blackbird 
Montezuma Oropendola 
Chestnut-headed Oropendola 
Montezuma Oropendola
See my Maquenque Birds 2020 Gallery from this trip with 61 species!
See also my Costa Rica Birds Gallery.
And for about the place, Maquenque Eco-Lodge & Reserve Website.
Or my travel gallery Maquenque Eco-Lodge July 2020 Visit
¡Pura Vida!