Jaguar

The jaguar is the largest cat in the Americas: a compact, muscular animal with a big rounded head, short sturdy legs and the shortest tail of any big cat. The coat runs from pale yellow to tan or reddish-yellow with a whitish underside, covered in black spots that become rosettes on the flanks; most rosettes enclose a small dot, which separates it from a leopard. Melanistic (black) animals occur, and size grows from north to south, so Central American jaguars are smaller than those of the Pantanal (Wikipedia, general species account).

Across its range the jaguar is a solitary stalk-and-ambush hunter that usually stays near rivers, lakes and swamps. It swims well, and kills with a bite through the skull between the ears or through the back of the neck; its jaws can pierce turtle shells and the hide of crocodilians. Telemetry studies elsewhere show variable activity: nocturnal in some regions, as active by day as by night in others, reflecting the activity of prey and the level of human disturbance (Wikipedia, general species account; GBIF species profile).

In Costa Rica the jaguar's range centres on the Osa Peninsula, and black jaguars have been photographed in the Talamanca mountains, including Barbilla National Park (Wikipedia, citing published records). It is rarely seen. On this guide it is a target species of Braulio Carrillo, Guanacaste National Park and Horizontes, and Corcovado.