Method: dip netting
According to eBird barcharts, this bird is supposed to be rare in Buenos Aires, at the southernmost tip of its range ... and yet there it was, foraging in and amongst the sidewalk cafes, totally unafraid of people.
This bird is banded (ringed) with color markers. I reported it to the USGS, but never heard back. If anyone knows whom to report it to in Argentina, please let me know.