I have found this bird in my house, I live in Haedo, Buenos Aires, Argentina. I tried to take a closer photo but it escaped flying. I am not sure how to describe it, but it's very big compared to normal birds.
That specimen in your photo seems to be the Southern Crested Caracara, Caracara plancus:
Also your location matches the range of C. plancus, which is from northern Brazil to Tierra del Fuego: