Confidence: It's likely to be this, but I can't be certain.
Notes: Working from Collins Illustrated Checklist of the Birds of South America and Antarctica and there are a number of similarities to the picture on plate 97 e.g. the white lower mandible, buff supercilium, brown streaked band across the breast, black undertail. The book picture shows it with a reddish breast - significant in the male and a smaller patch in the female but we should still see it in the above photo. I wonder if the photo is of a young bird?