Molothrus bonariensis -female- (Shiny Cowbird / Chamón)
True colours. The purple comes from a Tibouchina heteromalla shrub (Silverleafed Princess Flower). See the first comment.
The Shiny Cowbird has a very wide and expanding distribution in South America and the Caribbean. A brood parasite, the species lays its eggs in the nests of many species of passerines throughout its range, and provides no parental care for eggs or young. The male is entirely glossy violet blue-black or purplish black. The female dull grayish brown above.
Shiny Cowbirds often ride on the backs of cattle, horses, and sheep while feeding.