Predictors of Population Estimates in a Critically Endangered Species of Black-and-White Colobus Monkeys

Abstract

Population monitoring can help us determine population status and trajectory, but it is important to assess what factors may influence the number of individuals counted. In this study we conducted a complete count of the Critically Endangered Colobus vellerosus in the forests attached to the Boabeng and Fiema communities in central Ghana. We used 157 repeated counts of the same groups, including both good and unreliable counts to assess what factors predict the number of counted individuals in each group. The number of counted individuals increased with proxies for observation condition, observer experience, and habituation. We therefore recommend observer training and careful planning to increase the chances of having good observation. Then, we used the good counts to calculate the population size and group compositions. The obtained maximum number was 393 individuals in 25 groups. There were no significant differences in group sizes or immature to adult female ratios between groups occupying the older growth forest and groups in other forest types. Although there was still a relatively high immature to adult female ratio indicating that the population size may still increase, it does not appear to grow as rapidly as it used to, based on comparisons with previous population counts. Based on these findings, we recommend priority areas to promote conservation success.