Falkland steamer duck – Tachyeres brachypterus
is a steamer duck native to the Falkland Islands in the southern Atlantic Ocean. It is one of only two bird species to be endemic to the Falkland Islands, the other being Cobb’s wren.

The Falkland steamer duck’s wings are very short (hence the scientific name: brachy = “short”, and pteron = “wing”), and it is incapable of flight. The plumage of the Falkland steamer duck is mostly dark grey, but with a white stripe behind the eye. It is very difficult to distinguish from the flying steamer duck in the field since they occupy the same habitat and, although the flying steamer duck can fly, it rarely does.

It sounds like this
Recording by Andrew Spencer from Xeno canto