Date of Award

Spring 1-1-2013

Document Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Herbert Covert

Second Advisor

Dennis Van Gerven

Third Advisor

Michelle Sauther

Fourth Advisor

David Armstrong

Fifth Advisor

Barth Wright


This socioecologic study was on the red-shanked doucs (Pygathrix nemaeus) in Son Tra Nature Reserve, Vietnam. The doucs live in modular societies with stable groups composed of units. The average group size was 18 individuals and consisted of ~3 units with a daily pattern of fission-fusion. Units always fused overnight. Average unit size was 6.5 individuals. Home range was 36 ha with a core area of 8 ha. The average daily path length was 509 m, and path length was significantly and negatively correlated with precipitation. Social structures and organization are partly influenced by intergroup contest competition, ecological constraints including habitat quality and fragmentation, predation, and intragroup scramble competition. Concerning the activity budget for all individuals, inactivity was common (35.3%), followed by moving (28.6%), socializing (21.7%), feeding (13.7%) and self-grooming (0.7%). A compelling relationship was revealed between the daily activity budget and the daily pattern of fission-fusion between units. When units are fused they rest significantly more, and when fissioned they move, feed, vocalize, and are vigilant significantly more. This appears to be an adaptation to avoiding intragroup scramble competition and for maintaining contact and coordination between dispersed foraging units. Concerning the feeding budget for all individuals, leaves were most frequently selected (87.8%), followed by fruits and seeds (10.2%), flowers (1.6%), and bark/pith (0.4%). Young leaves were selected over mature leaves (68.6%), and whole leaf blades (86.5%) and petioles (13.1%) were more commonly selected leaf parts. Important food species were Parashorea stellata, Parsonsia laevigata, Ipomoea eberhardtii, Garcinia morella, Ficus variegata, Ficus depressa, and Ancistrocladus tectorius. Dietary diversity is low. Young leaves, and fruit and seeds, were not selected according to availability, suggesting that the doucs are selective foragers. Chemical and nutritional content of selected and non-selected leaves, and selected young and selected mature leaves, were not significantly different. The high quality of mature leaves might contribute to the high degree of folivory. These data have been helpful in the planning and implementation of various exhibitions, reforestation efforts, and the building of canopy bridges for the doucs to cross between habitat fragments on Son Tra Nature Reserve.