At 12-14in plus tail, the squirrel monkey is the smallest. Slender and agile, they roam the forest looking for insects, fruit and nectar from the ground right up to the highest branches.
They travel in small groups, making so many squeals, whistles and chirps that they are impossible to miss.
They are found so patchily that it is thought they may have been introduced from South America by man. Manuel Antonio NP is a good place to find them.
White-headed capuchin monkeys are the most commonly seen, sometimes together with squirrel monkeys.
Mid-sized (14-22in plus tail) they move in similar groups, gracefully, agilely, not calling much, but there is always plenty of movement in the branches to give away their presence. Their diet is similar, with wasps being a special favourite.
Black-handed spider monkeys are seen occasionally: they are larger usually generally black monkeys swinging by their arms from branch to branch mostly high up.
They need large forest areas and are considered threatened.
Mantled howler monkeys are truly wonderful. They are entirely black, with a pale frosted fringe of hair on their sides or lower back. The long throaty roars called by the lead males to coordinate their groups echo for miles.
You will usually find them sitting around or moving slowly (upright rather than hanging); their diet of fruit and leaves making for a comparatively stolid life.