Chupim, Chopim

Sergio, I think you are right ! I found some pics very similar. This bird is very interesting as it parasite the nest from other birds, puts his eggs inside and remove the original eggs. I will try to take a picture from a Tico-Tico nursing what it thinks is its "son".

Asergio, Molothrus bonariensis (Shiny Cowbird) does not have a long enough tail.