These tiny, playful primates are nicknamed squirrel monkeys. You can see them chattering and roughhousing with each other in the video below, which co-stars some befuddled, middle-aged Americans vacationing in Costa Rica.
The mono titi is one of the smallest monkeys, weighing in at only one to two pounds, and are described as "peaceful primates." Like their relatives the bonobos, they have an egalitarian society in which males share in parenting duties can stay with their natal group past puberty. Only about 1,000 mono titis remain (down from about 200,000 in the 1980s) due to habitat destruction by deforestation. The monkeys only live in mangrove forests and mountainous foothills, both of which have been increasingly fragmented by agricultural development and logging. There are also some indications that the monkeys are being captured for export as exotic pets, and hunted for food. The monkeys live in tightly-knit bands of 20 to 75 animals, so the poaching of even one individual can have social effects on the entire group.
Approximately 200 of the remaining mono titis live in the Manuel Antonio National Park nature preserve in Costa Rica, which uses ecotourism to fund conservation efforts. An unknown number also live at the Corcorvado National Park further south. To learn more about the mono titi, you can see a video about issues surrounding the Manuel Antonio population here.