Ontogeny of Positional Behavior in Captive Silvered Langurs (Trachypithecus cristatus)

Compared to most other mammalian groups, primates are known for the great diversity of positional behavior they exhibit. Their positional repertoire is not static through time, but rather changes with age. As primates age and body size increases, the manner in which animals navigate their environment responds to shifting biomechanical, nutritional, socio-behavioral and reproductive factors. In this study, I examined positional behavior in a colony of captive colobine monkeys, hypothesizing that locomotor and postural diversity will increase with age due to changing physiological and ecological processes. I predicted that as animals mature, their positional diversity will increase as they become more adept at negotiating their three-dimensional environments. I examined age effects on positional behavior in silvered langurs (Trachypithecus cristatus) housed at the Columbus Zoo. Data were collected from January – August 2009 using instantaneous focal animal sampling on a breeding group containing four adults, two juveniles, and one infant. During each scan I recorded the focal animal’s identity, maintenance activity, substrate, and postural (19 categories) or locomotor (12 categories) behavior. Chi-square tests were performed on the data set of 4504 scans. Contrary to expectations, my analyses show that the number of observed positional behaviors did not change significantly with age, although the types of behaviors observed did change. Younger individuals displayed a greater range of behaviors while demonstrating elevated frequencies of climbing (p = 0.0065) and leaping (p = 0.0004). Use of hindlimb postures also showed an age effect, with propped-foot sitting becoming increasingly common in older individuals. Behaviors not associated directly with age may be explained by interacting factors, including age, sex, and reproductive state. I conclude that in this captive group of silvered langurs, diversity of positional behaviors and frequencies of specific locomotor activities covary with age, but that captive environments may be responsible for results at odds with those obtained from free-ranging populations.SBS Undergraduate Research GrantNo embarg