Good news!!! Now (year 2021) the answer to such questions is VERY easy, as the long awaited Mark Pearman's (with the addition of Nacho Areta as coauthor) field guide to the birds of Argentina and the South-west Atlantic has seen the light and it's as amazing as we were expecting it to be. It includes comprehensive information about 1075 species of birds (they missed at least one, which was first recorded in the country after the book was sent to print: the Andean Ibis - Theristicus branickii - showed up in North-west Argentina) and outstanding illustrations from four different artists, including two of the best Argentines: Aldo Chiappe and Jorge RodrÃguez Mata.
Printed by Helm and Princeton field guides, you can order yours in the following links (just in case, I don't get any commission from this...):
- Helm Field Guides: https://www.nhbs.com/birds-of-argentina-and-the-south-west-atlantic-book
- Princeton Field Guides: https://press.princeton.edu/books/paperback/9780691147697/birds-of-argentina-and-the-south-west-atlantic
WHAT ABOUT MOBILE APPS?
Apart from the previous printed book, I also recommend to download Merlin app. It's very helpful as it will add good quality photographs plus great sound recordings that you can study before your trip. This app is famous for its automatic photo ID recognition, but even if you don't wish to use that function, it's a fairly well done field guide that you can bring in your mobile for no cost (yes, it's completely free).
The pack for Argentina is available since 2020 and it has a big percentage of the species, but if you want to have them all (or almost), then also get the packs for Bolivia, Chile and South Brazil. You will get many species that are not found in Argentina (especially with the Bolivian pack) but that shouldn't be a problem.
WHAT IF YOU ALSO PLAN TO VISIT ANTARCTICA AND SOUTH GEORGIA?
Although Pearman & Areta's field guide does not include such places, it does cover ALMOST all species found down there, with a few important exceptions: South Georgia Pipit, South Georgia Cormorant and Antarctic Cormorant (both of them considered by many as subspecies of Imperial Shag) and the South Georgia subspecies of Yellow-billed Teal (a possible future split?). If you feel like you need to have these species in a field guide during your trip, my recommendation is to bring Alvaro Jaramillo's guide to the birds of Chile (which includes the Malvinas/Falklands, Antarctic Peninsula and South Georgia island). It will also be very useful if you are planing to do some birding around Ushuaia and in the Patagonian forest of both sides of the Andes, but it gets completely useless for other parts of the country (except maybe for the high altitude Puna wetlands of the North-west, and the high Andes along the Central-west part of Argentina). The last English version is a bit outdated (2003) but it is still, in my personal opinion, the best available field guide to the birds of Chile, because of the quality of the texts and information included, the great illustrations and its compact user-friendly size.
Here is a link to one of its printed versions: https://www.nhbs.com/birds-of-chile-jaramillo-burke-beadle-book (do not confuse it with the newest Helm field guide to the birds of Chile, which was made by other authors)