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Sporophila corvina
I think this might be a male and female pair.
Looks like being Sporophila corvina, Variable Seedeater. Formerly it was called Sporophila americana or Sporophila americana corvina. I think Sporophila corvina is the actual taxon.
https://en.wikipedia.org/wiki/Sporophila...
http://avibase.bsc-eoc.org/species.jsp?a...
http://neotropical.birds.cornell.edu/por...
http://ibc.lynxeds.com/species/variable-...