This is the world's largest grebe. An adult carries recently hatched chicks in a pocket on its back created by the folded wings while the other adult dives for food. They keep in contact by calling as seen here. Birds such as this from the southern tip of South America are the larger, darker headed race P. m. navasi. Digiscoped with Panasonic DMC-LX5 | Nikon FieldScope 3 | 30X WA | hand-held (no adapter)
Reference:
Llimona, F., del Hoyo, J., Jutglar, F. & Kirwan, G.M. (2016). Great Grebe (Podiceps major). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/52487 on 25 December 2016).