Estimating the Abundance of Clustered Animal Population by Using Adaptive Cluster Sampling and Negative Binomial Distribution Yizhou Bo*, Naima Shifa** * Department of Mathematics, DePauw University, Greencastle, IN, USA 46135, yizhoubo_2014@depauw.edu ** Department of Mathematics, DePauw University, Greencastle, IN, USA 46135, naimashifa@depauw.edu To maintain the balance in nature, to meet the challenges of sustaining life on earth, or to provide sound and effective public policy, researchers always would like to estimate the density or the total of natural populations. It is not always easy and straightforward to obtain the abundance of animal populations when the study area is vast and animals are clustered and mobile. In this research work, we propose a multistage stage sampling design for estimating the animal populations that spread over an extensive area, and highly clustered. This model is based on adaptive cluster sampling (ACS) to identify the location of the population and negative binomial distribution to estimate the total in each site. To identify the location of the population we consider both sampling with replacement (WR) and sampling without replacement (WOR). Some mathematical properties of the model are also developed. Key words: Adaptive cluster sampling, negative binomial distribution, sampling with or without replacement, rare or clustered population, population size estimation.