This plucky wee Tyrant Flycatcher quickly became a favourite of ours.
Oropendolas & Caciques are Icterids -a family that includes many pernicious brood parasites such as the cowbirds. The Piratic Flycatcher goes some way to redress the balance as it displaces Caciques & Oropendolas from their nests by sheer persistent harassment of the rightful owners. They steal nests but are not true brood parasites (but they do eject any eggs present at the time of appropriation).
Piratic Flycatchers, unlike most other Tyrannidae eat mainly fruit which can be quickly gathered & gorged leaving much time to sit on exposed perches singing & beating up any passing Oropendolas (a bird many times bigger).