The Black-cowled Oriole is one of three similar resident species in Costa Rica, the other ones being Spot-breasted Oriole and Streak-backed Oriole, however both of those have markings as their name indicate, while the Black-cowled has black chest and head, along with the back and wings. They look bigger than Tanagers due to their long tail. In poor light, they can be confused with the Baltimore Oriole, but the Baltimore is migratory (does not occur from May to September) and the Black Cowled is only frequently observed in the north plains and the Caribbean side (Baltimore turns up anywhere in the country during migration).
I personally have seen this species once at Fincas Bambuzal, Rio Frio, and also at Laguna del Lagarto Lodge, Boca Tapada. Adults shared the feeder with Honeycreepers, Tanagers and the Baltimore Oriole. All of them abandoned the feeder when the Toucans arrived, or when any bird sounded the “Hawk” alarm call.