Help identifying this bird from Southern Brazil
That is Syrigma sibilatrix, the whistling heron. In Brazil we call it "maria-faceira".



Here is Syrigma sibilatrix page in Wiki Aves ("aves" is birds in Portuguese): http://www.wikiaves.com.br/maria-faceira 

Wiki Aves is by far the best source for birds in Brazil. It is a very well documented and reliable source, maintained by great ornithologists.

PS: Regarding the Southern lapwings: they are not really attacking, they are just trying to drive off the intruder. And there is a reason: the lapwings nest on the ground. I was "attacked" by them several times (I'm from the Southern Brazil), when I inadvertently approached their nest.