I don't know if there are field guides on the birds of South America as a whole, as it's a very big area and the number of species involved is really high. I know good quality field guides for several countries or areas, like Brazil, Chile, Cuba, etc. I have one very good on the birds of Chile, which is:
JARAMILLO, Á., P. BURKE & D. BEADLE (2003). Birds of Chile including the Antarctic Peninsula, the Falkland Islands and South Georgia. Helm Field Guides. Christopher Helm. London. 240 pp.
On the other hand, you can search for such books in the NHBS website, which is one of the best book suppliers of Natural History in the world...