The Andean Coot or Slate-colored Coot, Fulica ardesiaca, is a species of bird in the Rallidae family. It is found in Argentina, Bolivia, Chile, Colombia, Ecuador, and Peru. Its natural habitats are swamps and freshwater lakes. The bill and shield color is variable. The most common combination is a chestnut shield and yellow bill. Other combinations are yellow shield / white bill and white shield / white bill.
When I saw these in the marsh I through, “Just another Coot” not realizing it was a separate species than the Coot in North America. When I got home and realized my mistake I looked and found one fair photo of an Andean Coot.