Mantled howler monkey (Aouatta palliata palliata) Positional Behaviors in Relation to Substrate Diameter and Angle of Incline

My research question was if substrate diameter and angle of incline, in relation to most often the trunk of a tree, would affect positional behaviors of mantled howler monkeys (Alouatta palliata). In pursuing this research question I wanted to understand more the effects of diet, specifically low quality diet, on primate locomotor and postural behaviors and how this might impact primate behaviors according to what foods are available. To test my research question, I collected observational data from adult howler monkeys, to see how they influenced locomotive patterns. I divided the substrates, in this study being tree branches, into 4 categories: greater than 45°, less than 45°, 90° and 180°; I then divided substrate diameters into sizes relative to the observed individual’s body: extra-large, large, medium and small. For predictions I suggested that due to the generalized body plan of howler monkeys, they would most likely utilize quadrupedalism if a substrate was 180° or greater than 45°, but if a substrate was less than 45° individuals would utilize a tail-hanging posture; I had no prior predictions for what positional behavior would be used if a substrate was 90°. My predictions stemmed from the fact that howler monkeys have a generalized body plan which, coupled with their low nutrient diet, keeps them from having locomotive and postural behaviors that primates with more specified body plans would use. I found that overall, observed individuals utilized a quadrupedal locomotive behavior while occupying over all 4 categories of substrate angle. I observed that individuals exhibited a hindlimb tail hanging posture the majority of the time. The lack of postural behaviors I attribute to a generalized body plan as well as the substrate diameter; most substrates occupied were either large or medium in relation to body size