Document Type
Thesis
Date of Degree Completion
Spring 2026
Degree Name
Master of Science (MS)
Department
Primate Behavior
Committee Chair
Dr. Lori K. Sheeran
Second Committee Member
Dr. Jessica A. Mayhew
Third Committee Member
Dr. Citlalli Morelos-Juarez
Abstract
Ecuadorian spider monkeys (Ateles fusciceps) are among the least-studied platyrrhines and the world's most endangered primates. These monkeys are increasingly threatened by habitat loss due to logging and timber extraction for land-use change to monocultures, as well as by hunting. No research has been published on their sleeping behavior, which is an integral aspect of their lives. We examined whether A. fusciceps at the Tesoro Escondido Reserve in Ecuador exhibits a pattern of use of sleeping trees. Subgroups were followed 5-6 days a week for 10 weeks. After we located a sleeping site, we recorded the number of trees used by the monkeys and the number of monkeys per tree. We identified the genus and species of sleeping trees and measured tree characteristics, including tree height, diameter at breast height (DBH), distance from the ground to the first branch, canopy coverage, canopy connectivity, and the presence of epiphytes on the trunk and branches. There were 18 recorded uses of sleeping tree (15 unique and 3 reused). The average height and DBH of sleeping trees were 40.3 m (range 35-48 m, SD = 5 m) and 115.5 cm (range 83-260 cm, SD = 51 cm), respectively. Eleven of the sleeping trees were the genus Brosimum, and eight of those eleven were Brosimum utile. Trees of the genus Brosimum are large and considered important food sources for spider monkeys. The reused sleeping trees were B. utile (n = 2) and B. rubescens (n = 1). My findings suggest that sleeping trees were selected for characteristics that aid in predator avoidance and detection. Their sleep trees were significantly taller, had larger DBH, had greater distance from the ground to the first branch, had less canopy coverage and canopy connectivity, but no significant difference was found in epiphyte presence on trunks and branches. We observed an average of 2.6 individuals (range 1-5 individuals, SD = 1 individual) per sleeping tree, and the spider monkey group was never observed sleeping in a fusion state. These findings help identify key tree species that need protection to support the conservation of Ecuadorian spider monkeys.
Recommended Citation
Skinner, Kyler J., "Sleeping Tree Selection and Sleeping Tree Group Sizes of the Critically Endangered Ecuadorian Spider Monkey (Ateles fusciceps) in Lowland Ecuadorian Chocó Forest" (2026). All Master's Theses. 2364.
https://digitalcommons.cwu.edu/etd/2364