Caldecott, J. O. 1986. An Ecological and Behavioral Study of the Pig-Tailed Macaque. Karger, Basel, Switzerland.

Excellent overview of the species-typical behavior of wild pig-tailed macaques. Groups did not appear to select particularly large or emergent trees, but sleeping sites tended to be clumped on the upper part of the hill (which is to say, away from the forest edge). They were generally entered as dusk fell. Animals spent 8-10% on the ground, 26-34% in the lower canopy, 47-60% in the middle canopy, and 4-11% in the upper canopy.