Scarlet-bellied Mountain-Tanager, Anisognathus igniventris
The Mountain-Tanagers are especially colorful, and this one is no exception -- the adult, above, is "vivid scarlet" (Ridgely and Greenfield) on belly and auriculars, with bright blue shoulders and rump, and otherwise coal black. Immature birds, shown in the two photos below, are more orange in part or whole where the adult is scarlet, and with a less dark black.
