There several passerines which are black with some colouring which facilitates identification. Sometimes it is exposed, sometime it may be hidden and the habitat or the behaviour help to determine it. The vocalizations are crucial but if they are in silence.... Here the nine most common species of Costanera. They are: spectacled tyrant, solitary black cacique,. chestnut-capped balckbird, unicoulored blackbird, yellow-winged blackbird, white-lined tanager, shiny cowbird, screaming cowbird and variable oriole 

Yelloweish eye-ring and bill. In trees and open spaces

Ivory bill. In trees

Chestnut crown and bib. In marsh vegetation

Whitish lower mandible. In trees

Brown spot on the shoulder. Acrobatic. In trees

Two Agelasticus, two very similar birds. The difference is the yellow spot on the should of the yellow-winged blackbird. Depending on the posture this spot may remain hidden. So if there is no spot in sight, it is advisable to wait for the bird to move to confirm the presence or absence of the spot. The  long and pointed bill distinguishes blackbirds from cowbirds. Both species present sexual dichromatism (male and female are different).

Two Molothrus. Plumage of the shiny cowbird with violacious and bluish tones the screaming cowbird lacks. In the sun the iridiscence becomes evident. The black colouring of the screaming cowbird is glossy and uniform. In unfavourable light conditions attention is needed. The chestnut iris of the screaming cowbird contrasts with the shiny cowbird's dark iris. The bill is conical in the two species. Shorter in the screaming cowbird. Both form flocks. In the reserve the number of screaming cowbird is very small and may be found together with the shiny cowbird.