The reproductive success and viability of arboreal primates will depend on the correct selection of nesting sites. The night monkey Aotus zonalis, presents an interesting adaptation as it is not only cryptic and arboreal, but also nocturnal. In this work we describe part of their behavior and analyze variables that could be influencing the selection of nesting sites. A group of A. zonalis was observed in a fragmented forest in the north of Cocle province, Cerro Colorado, Pajonal, Panama (N 08º34'44.8'' O 80º13'42.0''). We carried Ad libitum observations and Strip Transect (768 hrs.), using red light and nocturnal walks, and Orion Camera System (SCO) (8,760 hrs.), from May 2017 to May 2018. The group structure was a pair adults (male/female), and a juvenile, living together in a 3 km2 patch of forest.

Three nests were located and with data on only one nest. The entrances (Kruskal-Wallis: p=3.161E-06 ; p <0.005) and exits (Kruskal-Wallis: P=0.001113; p <0.005), were not significant and depend on three variables (moonlight, rain and temperature), the temperature is decisive. There was a main use of the nest in the rainy season, and we detected copulation and male parental care. The most used plants for nests were Bactris gasipaes and Cydista aequinoctialis. Diplomis labilis was reported as a species sharing habitat. These initial works will provide long-term monitoring for more robust studies and conservation programs for this species in Panama. Keywords: Aotus zonalis, Circadian activity, Orion Camera System, Nocturnal, Panama