Positional Behaviours of Francois' Langur (Trachypithecus francoisi) in the Limestone Forest of Nonggang, Guangxi, South-West China

Primates' positional behaviours provide information for understanding relationships among morphology, ecology and behavioural flexibility. From September 2005 to August 2006, we collected data via instantaneous scan sampling on positional behaviours in Francois' langurs at Nonggang Nature Reserve, south-west China. We predicted that these langurs would use (1) leaping as the predominant locomotor mode and (2) bipedal standing more frequently in the rainy season than in the dry season. Our result showed that leaping was the dominant locomotor mode (38.38%), followed by -quadrupedal walking (31.2%), vertical climbing (25.1%) and quadrupedal running (5.3%). The ground was the most frequently used stratum during movement (33.4%). Most locomotion through trees occurred on small- (48.7%) and medium-sized (47.6%) substrates. Locomotor mode, forest stratum use and substrate use during movement did not vary seasonally. When stationary, sitting was the most common posture (92.1%), followed by bipedal standing (3.7%), lying (3.5%), quadrupedal standing (0.6%), suspending (0.2%) and back-lying (<0.1%). Posture varied significantly with the season. During resting, langurs used sitting and bipedal standing more frequently in the dry season, while adopting lying more frequently in the rainy season. During feeding, sitting was adopted more frequently in the rainy than in the dry season, whereas bipedal standing was used more frequently in the dry season. Langurs spent more feeding time on the ground in the dry than in the rainy season. Locomotor patterns in Francois' langurs are likely linked to morphological and anatomical characteristics, along with the limestone forest's structure. Our result completely supported prediction 1 but not prediction 2. This study suggests that seasonal variation in positional behaviour might result from the temporal difference in spatial distribution of foods and behavioural thermoregulation strategy. We found that Francois' langurs adjusted positional behaviour in response to seasonality, and this behavioural flexibility allows them to survive in a variety of habitats, including limestone forests.