Three primates (Hoolock gibbon, Bunopithecus hoolock; Capped langur, Trachypithecus pileata and Pigtailed macaque, Macaca nemestrina ) were studied in a semi evergreen forest of Trishna Wildlife Sanctuary, Tripura for estimating site occupancy and modeling their co-occurrence pattern. Thirty five (35) sites representing six (6) distinct habitat types were monitored seasonally (2 seasons) six (6) times between 2002 and 2004 for all the study animals and their associated habitat variables. Sample covariates were quantified during each sampling where as site covariates were measured seasonally once in 79 permanent sampling plots to represent the habitat characteristics of 35 sites.

As quite often, animals remain undetected due to the low visibility factor and nature of the study animal even though they are present in a particular site, detection probability was less then one. Approach discussed here is the first attempt to account explicitly for the imperfect detectability of species while modeling three primate species occurrence data. Site used, occupancy rates and co-occurrence patterns for study animals have been calculated for two consecutive breeding seasons using model developed by MacKenzie and Ecosim software. Multivariate statistics were used to discuss the results obtained from above method.

Habitat types classified mainly based on the tree cover and other covariates showed that no two types were more than 20% similar. Savannah woodland present in the southernmost part of the Sanctuary is not inhabited by any of the primate species under study. In rest five habitat types detection probability calculated for all the primates were very low (<0.25). Changes in the proportion of different sites and habitats used by the animals were negligible incase of capped langur and pigtailed macaque, whereas hoolock gibbon showed significant decrease in the site occupancy during second year of study. Only in mixed deciduous forest habitat with maximum tree diversity in this area showed strong association among three study animals in terms of spatial scale but were segregated in temporal scale. Inferences from this model on species occupancy and co-occurrences in different habitats hold good but to draw strong inferences on the process of changes of patterns of occurrence requires a long term study.