This is an adult. The Jacanidae are an interesting assemblage of tropical water birds with extraordinary long toes and claws which allow them to spread their weight so they can walk on lily pads and other floating vegetation. The name "Jacana" is a Portuguese word based on the Tupi Indian name for the bird. It supposedly should be pronounced Zha-seh-NAH but very few people pronounce it that way. A poll conducted by one web site found that most people pronounce it Jah-KA-nah, but that was out of a sample size of only 66 participants. It is often spelled Jaçana so the "c" should probably be soft. My recommendation is to abandon this odious name entirely and use an alternate such as "Lilly Trotter" or the more evocative "Lotus Bird."
Like other Jacanas, the Wattled Jacana is polyandrous with females defending territories that may have multiple nests and multiple males who incubate the eggs and care for the young. They are rather uncommon in the Pantanal, possibly because they are prey of the abundant Jacare Caimans. Six subspecies are usually recognized differing in the amount of black in their plumage. The northernmost birds from Panama and Columbia have black upperparts. This is the chestnut-backed nominate race.
Reference:
Jenni, D.A. & Kirwan, G.M. (2015). Wattled Jacana (Jacana jacana). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona.
Nikon P510